U.S. Rocket Ordnance, Development and Use in World War II

[U.S. Rocket Ordnance, Development and Use in World War II]
[From the U.S. Government Publishing Office, www.gpo.gov]

ROCKET ORDNANCE

DEVELOPMENT

AND USE IN WORLD WAR II

Released by the Joint Board on Scientific
Information Policy for:

OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT

WAR DEPARTMENT

NAVY DEPARTMENT

For Release by Press and Radio after 7 P. M.z E. S. T.z 30 March 1946. (For Sunday Morning Newspapers of
March 1946.)

u. s.
ROCKET ORDNANCE

DEVELOPMENT
AND USE IN WORLD WAR II

Released by the Joint Board on Scientific
Information Policy for:
OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT
WAR DEPARTMENT

NAVY DEPARTMENT

CONTENTS

Page
Foreword—Rockets at War............................. 1
1. “The Rockets’ Red Glare ...” ................. . 3
2. Rocket Fundamentals................................. 5
3. Organization of Rocket Laboratories.................10
4. Rocket versus Submarine.............................15
Mousetrapping the U-boat .......................15
The Rocket that Fired Backward..................17
Forward-firing Rockets Hit the Sub..............19
5. Rocket Armament for Aircraft........................21
“Tiny Tim”—a Really Big Rocket .................21
Role of Aircraft Rockets .......................21
U. S. Development Program.......................23
Aircraft Rockets Write Combat History...........28
6. Rockets for Amphibious Warfare......................33
The Crucial Interval ...........................33
Action at Okinawa...............................33
Barrage Rocket Development......................34
The Japs Meet Barrage Rockets...................36
Rocket-firing PT Boats..........................37
The Spinner Family..............................39
7. Bazooka versus Tank.................................41
8. Rockets for Ground Warfare..........................45
9. Specialized Uses of Rockets.........................51

III

Foreword: Rockets at War

If any one weapon symbolizes the flaring crash and swift destruction of World War II it is the rocket.
Every major participant used rockets. Each nation developed rocket weapons in answer to its tactical and combat needs. The Russians pioneered in the firing of antitank rockets from planes and in the use of massed banks of rockets for preassault barrages. The British used rockets for defense against attack from the air at a time when there were only 500 antiaircraft guns in the United Kingdom. With their Luftwaffe driven from the skies, the Germans employed the long-range V-2 weapon to attack England’s cities. The Japanese futilely attempted to use rocket artillery to defend their island outposts.
The United States, too, developed and introduced a great variety of rocket weapons. By the time the war ended, American soldiers, sailors, and marines had fired millions of rockets at the enemy. For those rockets, our armed forces could thank the teamwork of American science, industry, and the military at home.
When the Japanese attack on Pearl Harbor catapulted the United States into the war, our Army and Navy had not a single rocket in service use. Plans for rockets were limited. By VJ-day, the Army was procuring rockets at the rate of $150,000,000 a year. The Navy had 1,200 war plants turning out rockets at the rate of $100,000,000 a month.
“Tiny Tim”, a 1,200-pound aircraft rocket, a weapon which gives a fighter plane the punch of a 12-inch gun; other aircraft rockets; a “Super-Bazooka,” more lethal and accurate than the original infantry weapon; the Navy’s new rocket gunboats, the LSM-R’s, firing 5-inch spin stabilized rockets from automatic launchers at the rate of 300 rounds per minute.
One of the most spectacular rocket weapons of the war was the German V-2. Allied technical intelligence provided information about the V-2 more than a year before it finally hurtled out of the stratosphere to strike London. To counter it, about all we could do was to attack the launching sites with every means at our command.
The Germans had been working on such a rocket since 1935. We had not. To start from scratch in 1943 to develop a similar American weapon would have required several years of intense research effort on the part of our scientists in order to provide the fundamental design data which German workers had accumulated over many years. The tactical importance of such a weapon to the Allies was not great enough to warrant the diversion of scientific manpower already thinly spread over a vast military research program which included the development of the atomic bomb.
The American rocket workers, both military and civilian, had to go at their job “cold.” They had no store of basic data such as

Battleship of the Air describes this Navy. F6F plane which drives toward the target with a pair of “Tiny Tim? rockets—10 feet long projectiles that carry as much high explosive as the projectiles of 1%-inch naval rifles (BuA189952}.

an adequate program of peacetime preparedness would have given them. Were it not for the fact that the British had been more foresighted than we, had done experimental work with rockets before the war, and shared with us their knowledge and experience, the task of providing our fighting forces with rocket weapons would have been even more difficult and time-consuming. As it was, the job was hard and long enough, with every new project and improvement requiring an initial phase for the development of fundamental facts which a more complete program of peacetime military research would have developed in advance.
It is a tribute to the determination of the Army and Navy, to the imagination of American scientists, and to the productivity of American industry that, starting under such a handicap, they were able to produce the rockets which hunted down enemy subs in the Atlantic and Pacific, the bazooka which was first turned loose against the enemy in North Africa, the aircraft rockets which spearheaded the Normandy break-through in July 1944, and the barrage rockets which laid down a deadly fire ahead of our forces invading North Africa, Sicily, Italy, Normandy and Southern France and which softened the Japanese beach defenses for our landing waves in virtually every Pacific action from Arawe to Okinawa.
The rocket program which could produce such results was possible only because of the close cooperation among the Army and Navy and the National Defense Research Committee of OSRD. Under Division 3 NDRC, two groups of civilian scientists and engineers concentrated on rocket research and development. The first of these groups, for brevity, referred to in this report as Section H, originally had its headquarters at the Naval Powder Factory at Indian Head, Md., and later at the Allegany Ballistics Laboratory at Pinto, W. Va. The second group, the key personnel of which were largely recruited from the staff of the California Institute of Technology, made their headquarters at the Institute in Pasadena, California.
The Army and Navy participated more and more as rockets came out of the laboratories on their way to war. Many sections of the War and Navy Departments took on functions connected with rockets. Among the Army field establishments which participated prominently in the problems involved in providing safe and effective rockets to our forces were Picatinny Arsenal, Aberdeen Proving Ground, Wright Field, and Dover Army Air Base, the last with a branch at Muroc, Calif. Naval establishments active on similar problems included the Naval Proving Ground at Dahlgren, Va., the Naval Air Station at Patuxent, Md., and the Naval Ordnance Test Station at Inyokern, Calif.

1. "The Rockets* Red Glare ...”

The rockets of World War II represented not the invention of a new weapon, but the modernization of an old one.
The Chinese are recorded as having launched rockets against the Mongols as long ago as the year 1232.
By the close of the thirteenth century, knowledge about rockets had traveled from the Orient to Europe and, a hundred years later, was fairly widespread. Rockets were used to set fire to buildings and to terrorize the enemy. But as cannon were developed, rockets came to be used less and less in warfare and, for many years after 1500, were employed only for signalling or for fireworks displays.
Crude rockets reappeared as a weapon toward the close of the 18th century in India where native troops used them against the British.
Since the surest way to stimulate interest in a new weapon is to find it in the hands of the enemy, it is not surprising that the British quickly undertook to develop military rockets of their own.

Congreve’s Rocket
The British met with indifferent success until, in 1801, Sir William Congreve became interested in the problem. By 1805 he had rockets ready for service use. During the Napoleonic Wars, British warships launched rockets against Boulogne and Copenhagen, and they were also used with effect at the siege of Danzig and the battle of Liepzig in 1813.
Americans have a personal as well as historic interest in these British rockets. During the War of 1812, at the battle of Bladensburg, the raw American militiamen defending Washington broke under the flanking fire of British rockets, leaving the way open for the invaders to enter and burn the national capital.
Three weeks later, the British fleet attacked Baltimore. The story of Francis Scott Key needs no retelling—his detention on a British vessel in the harbor, his anxious night spent watching the bombardment of Fort McHenry and its “Star Spangled Banner,” and his immortal expression of pride that the attack failed. What is worth pointing out is that the “rockets’ red glare” of the National Anthem is not a phrase, born of a poet’s fancy. For the British fleet included several vessels equipped for rocket firing. The rockets and their red glare were the real thing.
Though the Congreve rockets were erratic missiles, their author was a zealous believer in their future. Others shared his faith. Rocket units sprang up in a number of European armies. In the United States, too, a rocket battery was created in 1846 and 10 more were organized the following year.

Hale’s Spining Rockets
It was in 1846 that an American, William Hale, made a significant improvement in design by substituting for a stabilizing stick three curved vanes attached to the rear end of the rocket. The propelling gases in flowing past the vanes made the rocket rotate about its longitudinal axis. Thus, Hale produced the first spinning rocket.

Two thousand of the Hale rockets were made in 1847 and saw service in the Mexican War. They were used in a landing near Vera Cruz and in the storming of Chapultepec, but little further information about them is contained in the records.
Despite a promising start, rockets as weapons went out of use soon after 1850. With the propellent powder then available, their development had been carried about as far as possible. Improvements in artillery—rifled gun barrels which increased accuracy, and mechanisms to absorb recoil—established a standard of efficiency with which rockets could not compete.
It was not until 1918 that rockets for warfare reappeared, and then only briefly. In that year, the late Dr. R. H. Goddard—often called the father of American rocketry—under the auspices of the Smithsonian Institution, undertook the development of artillery rockets for the United States Army. Associated with him was C. N. Hickman, then a graduate student of Physics. The two made and fired a number of test models, and were at work on a plane-to-plane rocket, when World War I ended. Official interest evaporated, and the project was dropped.

Between Two Wars
Little attention was paid to rockets of any kind during the twenties. The individuals and groups who did emerge as rocket enthusiasts in Europe and the United States were absorbed for the most part in trials of liquid fuels and dreams of interplanetary travel.
Beneath an outward indifference, however, an official interest in rockets began to develop in certain European countries. As became apparent later, England, Germany, and Russia were all aware of the military potential of rockets. England, for example, started experimentation in earnest in 1936. But all such work was carried on in closest secrecy, and little or nothing was known of it until after the outbreak of World War II.
In the United States, during the thirties, Lieutenant (now Colonel) Leslie A. Skinner of the Army Ordnance Department held so firm a belief in the future of military rockets that he did considerable experimenting on his own initiative.
By June 1940, France had fallen; England’s situation was desperate ; and the United States was confronted with the grimly vital task of mending overnight its neglected defenses. Dr. Hickman, now a member of the Bell Telephone Laboratories staff, recalled the reasons which had motivated the development of rocket weapons more than £0 years earlier. These reasons seemed even more convincing in the light of the new blitz weapons which World War II had produced. He wrote to Dr. Frank B. Jewett, head of Bell Laboratories and also president of the National Academy of Sciences. He listed the possible military uses of rockets and their advantages. Dr. Hickman’s letter set in motion the machinery which resulted in the sponsorship by the National Defense Research Committee of the program which provided America’s rocket weapons for World War II.

2. Rocket Fundamentals

A rocket is a missle propelled by the high speed, rearward expulsion of gases generated by the combustion of an internally carried fuel.
Newton’s Third Law—A rocket works in obedience to the natural law first recognized in the late Seventeenth century by Sir Isaac Newton who propounded, as the third of his “Laws of "Motion”: “For every action, there is an equal and opposite reaction.”
The action of the gases from the burning fuel, in pushing rearward out of the rocket, is matched by an equally forceful reaction which pushes the rocket in a forward direction opposite to that of the flow of the gases.
It is this reaction force which causes a rocket to fly through the air. It is not the push of the escaping gases against the atmosphere. A rocket can operate in a vacuum. In fact, it flies faster, the thinner the air, because there is less atmospheric resistance.
These principles hold equally good with the simple Fourth of July rocket and the German vengeance weapon, the V-2.

True Rockets
Rockets are a special branch of the jet-propelled family. The V-2 was a true rocket in that it carried within itself (in a separate tank) the oxygen required for the combustion of its liquid fuel. The V—1, like most jet aircraft, depends on the atmosphere for its oxygen; strictly speaking, it is not a rocket.
The American military rockets discussed in this report are all true rockets. They carry their own oxygen with them, though not, like the V-2, as a liquid in a tank. They are propelled by solid fuels— smokeless powders containing the necessary oxygen for combustion.

The Rocket’s Great Advantage
A principal advantage of the rocket is its lack of recoil.
Anyone who has fired a gun knows that the burning of the powder in the combustion chamber drives the bullet out of the barrel and that the reaction to this forward push against the projectile is a backward push against the gun—and the person or the gun-mount holding it.
Compared to a rocket, the speed of combustion in a gun and the gas pressure developed are extremely high.
Because of the recoil and the high pressure, guns and gun-mounts must be strong—which means weight.
A rocket is without recoil in the sense that no metal parts are pushed backward. One might say that a rocket reverses the recoil effect. It shoots gases backward at high velocity and is itself pushed forward by the recoil.
Lacking recoil, a rocket can be fired from a simple, light tube or trough which serves merely to point the rocket in the right direction when it starts its flight. As a consequence, rockets may be fired from structures which could not hold up the weight of a gun and its recoil-damping" mechanism, nor withstand a gun’s recoil force.
The comparatively light weight of rocket launchers gives the rocket a mobility enabling it to go many places impossible to a gun.

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Disadvantages of Rockets
Although rocket launchers are usually lighter than guns, the rockets themselves, because of their motor weights, are usually heavier than shell and bombs of equivalent size and effectiveness. For repeated firing from fixed locations, this weight differential may complicate the problem of ammunition transport.
The blast of high-temperature high-velocity gases from the rocket is a hazard and inconvenience. Launchers must be so mounted as to leave a clear space behind them, or blast shields must be provided. Also, the flash of rockets may reveal firing positions.
Many rockets are slower than equivalent gun projectiles and hence less effective in the penetration of hard targets.
Although forward fired aircraft rockets have accuracy comparable to that of guns, most ground-fired rockets do not; a large number of rockets must be fired to hit a point target. This lower accuracy in ground fire, however, is of little consequence when it is desired to saturate an area target.

Basic Data
Basically all of the rockets dealt with here consist of a head or payload, and a motor containing the propellant powder. Like shell and bombs, rocket heads include solid shot, and thin wall and thick wall types filled with high explosive, smoke, incendiary and chemical, or other agents. To produce the effects desired at the target, nose fuzes and sometimes base fuzes are used; these are similar in functions to those used in bombs and shell, but, because of the characteristics of rockets, are frequently different in construction and operation.
A look at an assortment of standard American rockets will show that their weights range from 3 to 1,300 pounds, their diameters from 2 to 12 inches, and their lengths from 1 to 10 feet. In many rockets, most of the length is in the motor. In some, the motor is of smaller diameter than the head.
Some rockets have radial or cylindrical fins mounted at the rear end. Functioning like the feathers on an arrow, these fins stabilize flight through the air. Each of these rockets has one or several nozzles at the rear, parallel to the projectile axis. Other rockets, which have more the proportions of artillery shell, lack fins. These have multiple nozzles set at an angle in the back end to import rotation in flight, so that they are stabilized by spin, like rifle projectiles.

Firing Behavior
The velocities of American military rockets vary from 65 to 1,500 feet per second and their maximum ranges in ground firing are from 40 yards to 10,000 yards.
All of these rockets, except those of the bazooka type, continue burning for distances many times longer than the launchers. Distances of burning vary from 3 feet to 1,000 feet for various rockets; corresponding durations of burning vary from 0.010 to 2 seconds. After burning has ceased, the rockets continue in free flight in the salne manner as do shell, with trajectories of similar curvature.

Powder, Grain, and Web
In the powder used to propel rockets three definitions are in order: Smokeless powder such as is used in rockets is a plastic material something like celluloid, composed of nitrocellulose and nitroglycerin, plus other ingredients to promote good burning. A grain of smokeless powder is a mass or body of powder of any shape and weight. Even though it weighs more than a hundred pounds, as some rocket charges do, it is still called a grain. Lastly, the web of a powder grain is the minimum cross-sectional thicknes between two boundary surfaces; the web thickness controls the time ^required to burn the grain.
The rate at which gases are generated by the burning of the propellant depends, for one thing, on the amount of exposed surface of the grain. To minimize the strength, thickness, and weight required in the motor wall to hold the pressure of the gases, it is desirable that the pressure during burning remain uniform,, without dangerous high-pressure peaks. This requires that the grain burn without changing its total exposed area, where all the burning occurs. Burning proceeds by parallel layers, preserving the general shape of the grain while reducing its thickness.
The simplest way to achieve a constant burning area is to give the grain the form of a tube. The exposed surface remains approximately constant, since, as the burning progresses, the exterior surface area of the tube decreases and the interior area increases. Another much used jcross-sectional form is that of a thick-armed cross, with portions of the arm surface “inhibited’ ’to prevent burning.

Pressure and Temperature Effects
Burning and pressure are interacting. Just as rate of burning affects pressure, so pressure affects rate of burning. The higher the pressure, the faster the powder burns. Thus the rate of gas production by the propellant and the rate of gas ejection through the nozzle must be in balance at a pressure below the strength limit of the motor.
The effects of propellant temperature on rocket performance and safety are much more marked than is the case with guns. The higher its initial temperature the faster the propellant powder burns.
At temperatures below the service minimum, the rockets fail to ignite, or burn only intermittently (chuff). At successively higher temperatures up to the service maximum, though velocity and range vary only slightly, acceleration increases and accuracy improves. At temperatures substantially above the prescribed service maximum, a proportion of the rocket motors will blow up near the launcher, with unfortunate results for personnel in the vicinity.
Rocket users rather understandably like to have temperature limits labelled on their ammunition.

Motor Components and Thrust
The principal components of a rocket motor are:
The propellant charge—One or several large powder grains—to generate high-pressure gases rapidly; the charge contained in the motor tube, which must withstand the gas pressure; one or more nozzles at the rear end of the tube—to control the pressure, direct the gas discharge in smooth rearward flow, and improve

thrust efficiency; and a powder trap or grid—to support and retain the charge during burning.
The gases generated by the propellant in a rocket motor exert equal pressure in all directions. Since they can «scape only toward the rear, there is an unbalanced force forward which provides about 70 percent of the thrust. In passing through a properly designed nozzle the gases expand to a lower pressure, with increased velocity, and by pushing against the outwardly flaring portion of the nozzle, they provide the remainder of the total thrust.

Headaches of the Rocket Designer
Rocket research has inquired into the behavior of rockets, into rocket materials and rocket processes. In particular, the rocketeer has had to deal with relationships among the many variables, and their limits.
Partly because the standard bombs and shells already available met so many of the requirements for rocket heads, and partly because other problems were more urgent, comparatively little work was done on heads during the war. The rocket designer’s main job frequently was to provide a motor which, when coupled to a head of specified weight, would give the whole rocket the velocity needed to deliver it to the required range.
This, though it may sound so, was no simple task. Perhaps the clearest way to see what the designer is up against is to picture him trying to make improvements in a rocket already designed.
If the payload is increased, velocity and range and perhaps accuracy, will be lost, unless a much bigger motor is provided. If the designer tries to lighten his motor to compensate for the increased head weight, he finds that it becomes less strong, and hence requires a reduction in the maximum temperature for service use. He may be able to improve the situation by the use of stronger alloys in his motor, but here-he runs into higher costs and, in wartime, shortages of critical materials.
If increased velocity for the same head is required, he thinks first of increasing the amount of propellant. But this will require a longer heavier motor. If he tries to pack more propellant into the same motor, he may find that he has choked off the gas flow; this increases the operating pressure and reduces the upper temperature limit. He may be able to use a thicker web powder, if it can be made available, with less surface and longer duration of burning, to get more propellant in without choking the gas flow.
If his rocket is fin stabilized and ground fired, this may result in less accuracy. He may try to use a smaller nozzle to shorten the burning time and hence increase accuracy—this increases the pressure and lowers the safe maximum temperature. For other reasons he may want to use a larger nozzle; he finds more ignition trouble when the rocket is cold. For certain applications he can solve some of his troubles by using a propellant of different composition.
During the war, and especially in the earlier phases, rocket designers had even less freedom of action. Research had extended the limits of the design possibilities, but these extensions could not be nut into practice until new plants were built to produce them. This was especially true in the production of thick web powder grains—a production “bottleneck” almost to the end of the war.

3. Organization of Rocket Laboratories

Dr. Hickman’s letter of 20 June 1940 to Dr. Jewett led to the initiation of American rocket development for World War II; the letter was remarkably prophetic as to the types of rockets ultimately developed, and their uses.
Dr. Hickman suggested that rockets might be fired from airplanes; that rockets could provide powerful weapons for the infantryman; that rockets launched from light vehicles and small boats would furnish firepower both intense and mobile; and that rocket motors could increase the penetrating power of armor-piercing bombs.
The proposals were submitted io the Army and Navy. The services expressed only mild interest, but agreed that Dr. Hickman’s ideas might be useful in connection with the propulsion of bombs. On this basis, Section H of Division A, NDRC, was set up on 26 July 1940, under the direction of Dr. Hickman. The first test shots were fired in September 1940 at the Naval Proving Ground, Dahlgren, Va.
Progress was rapid enough to show that rockets were indeed potentially of great value. Word came that the British had found rockets to be effective, particularly for high altitude antiaircraft fire. A British scientific mission, headed by Sir Henry Tizard, came to the United States in the autumn of 1940. Thus began the close cooperation and free interchange of ideas between American and British scientists which were of such great value in developing rockets as modern military weapons.

Indian Head
By the start of 1941, the rocket work had outgrown its first small quarters. Section H and the Navy established a rocket laboratory in a bomb-proof shelter from World War I, at the Naval Powder Factory at Indian Head, Md., where the lower Potomac River provided a range area.
In the summer of 1941, Dr. C. C. Lauritsen, then vice chairman of Division A, NDRC, went to England to investigate, among other things, British rockets. His trip led to NDRC’s decision to expand its rocket activities.
An additional NDRC laboratory at the California Institute of Technology started work in September 1941. The contract began under Section H, but was shortly transferred to another section. The work at CIT was under the general supervision of 11 faculty members. These professors of physics, chemistry, and engineering recruited a staff which grew to more than 3,000; they secured laboratory space on the campus, and land for powder making in nearby Eaton Canyon. For test firing the Army made available an area on the Mojave Anti-Aircraft Artillery Range near Barstow.
Beginning late in 1941, contracts for research and development projects were placed by Section H with selected institutions—including the George Washington University, University of Wisconsin, University of Minnesota, and Duke University—and with industrial concerns such as the Bell Telephone Laboratories, Hercules Powder Co., Budd Induction Heating, Inc., and Budd Wheel Co.
By the end of 1943, military interest in the rocket weapons developed

by these laboratories led to a host of requests from the Army and Navy for new and improved types of rockets. The work of the California Institute group had required a steady expansion of research and testing facilities.
And now it became necessary to increase the eastern facilities under Section H. At the beginning of 1944, the main Section H laboratory was moved from Indian Head to the new Allegany Ballistics Laboratory near Cumberland, Md., where operations commenced in February 1944, still under the OSBD contract with the George Washington University. The scientific staff was expanded by recruiting from both university and industrial laboratories.
The laboratories operated by Caltech and George Washington covered all aspects of rocket research and development; Hercules, Minnesota, Wisconsin, and Duke concentrated on propellant research; Budd and Bell were concerned mainly with the engineering design of rocket components and equipment.
Most of the rocket projects assigned to the CIT laboratory were of primary interest to the Navy’s Bureau of Ordnance. Full responsibility for these projects was given to the Institute group which carried the development of all components of complete rocket weapons, i. e., grains, motors, heads, fuzes, firing mechanism, and launchers, through all stages including pilot production in sufficient quantities for initial service use in training and combat.
Section H, on the other hand, shared the job of developing Army rocket weapons with the various development branches of the Army, such as the Ordnance Department, the Chemical Warfare Service, and the Army Air Forces. Under this division of the work, Section H devoted its principal efforts to fundamental research and motor development, while the Ordnance Department or other services developed all other components, and supervised all phases of weapon production.
Although the Section H program, as it developed during the war, included several projects for the Navy and for the Chemical Warfare Service, the gerater part of the effort went into projects carried out in cooperation with the Army Ordnance Department, to meet the needs of the Army Air Forces and the Army Ground Forces. All Section H rocket projectiles were designed to use multiple grain solvent extruded thin web charges. All Caltech rockets used dry extruded thick web grains. Except for “Tiny Tim,” the 1,200-pound aircraft rocket, all CIT rocket motors had single-grain charges.

First Project
When rocket development began in 1940, the only project in which the armed forces had expressed interest was the development of a rocket motor which would increase the penetrating power of the 14-inch armor-piercing bomb. .
The rocket motor for this bomb would not be hard to develop now, but in 1940—the rocket workers had first to develop the basic knowledge needed for proper design. They began their study of the internal ballistics of rockets. They had to develop special instruments and methods to study these factors. Precious time was consumed.
The first full-size rocket motor for the armor-piercing bomb was ready by the late spring of 1941, and a year later an improved model was ready for service standardization. But as was to happen on other

occasions during the rocket program, the rocket-propelled bomb project turned out to be a source of experience but not a military sensation. The tactical need for the weapon never became urgent enough to warrant its use in service against the enemy.
Work on the bomb, however, had high-lighted one of the first and worst problems confronting the NDRC rocketeers—the propellant. The only powders available for use as a rocket propellant consisted of double-base smokeless powders—roughly 60 percent nitrocellulose and 40 percent nitroglycerin, with a bit of diphenylamine added as a stabilizer—which were somewhat loosely called “ballistite,” from an early member of the family used in mortars.
Ballistite was the only commercial powder which had the high-energy content needed for rocket work. But the more serious problem lay, not so much in the properties of the powder itself—though it had a number of unfavorable characteristics—but in the fact that American powder manufacturers had neither the experience nor the equipment required to make the large, long-burning, thick-web grains required to give longer range and higher velocity to the rockets which the necessities of the war would surely decree.
The principal method of producing smokeless powder in the United States at that time was by the solvent-extrusion method, in which the powder ingredients were mixed with a volatile solvent to form a dough which was then pressed through dies into grains of the required shape. With this method, only thin-web grains could be produced. And thin-web grains imposed definite limits on the performance of the rockets they propelled.
On the first projects neither the Services nor NDRC wanted to wait to establish a new powder industry in the country; they concentrated first on the development of weapons using the solvent-extruded powders which could be provided in large quantities by the existing plants. By painstaking research, numerous improvements were made in this powder. Fairly early, Section H developed a “New Technique” or NT powder which was substantially better. By 1944 it was possible to secure a wide range of characteristics, including somewhat larger grains, by the solvent process.

Dry Extrusion

For many years British manufacturers had been making sizable, thick-web grains of cordite, the standard British smokeless powder, by a process of dry-extrusion. Without using a solvent, the dry cordite ingredients were mixed, rolled into a sheet, the sheet wound into a roll, and the roll—still dry—was placed in a press and extruded through a die at moderate heat and high pressure.
American manufacturers were inexperienced with this process: they regarded it—with some reason—as hazardous; and they lacked the massive equipment reouired. Hence the first emphasis was on solvent powder weapons. But NDRC did not neglect the promise of the thick web grains obtainable from the solventless or dry extrusion process. Section H initiated investigations of dry extrusion at Indian Head. However when the NDRC rocket program was expanded in 1941 the group at the California Institute undertook the major responsibility for development of equipment and methods for the dry extrusion of thick web grains, and of rockets using them.

One of the weapons which had particularly impressed Dr. Lauritsen on his visit to England was the British UP3 high-altitude antiaircraft rocket—a high-performance rocket using a single grain of thick-web, dry extruded powder. The development of a similar antiaircraft rocket was assigned to the CIT laboratories and therefore that group gave its primary attention to the development of techniques for the dry-extrusion of large ballistite grains.
By early 1942, the antiaircraft rocket had lost its priority in favor of other more urgently needed weapons. Nevertheless the experience gained was of inestimable value, for it “paid off” in the rapid development of other rockets, particularly the high-performance aircraft rockets.
With a quickly improvised press, CIT workers demonstrated the feasibility of dry-extruding ballistite grains from trench mortar sheet powder. In rapid succession, there followed a series of scientifically designed presses of increasing sizes. These pilot presses were kept in continuous operation supplying grains for all types of new rockets— first during the development stages and later in quantities sufficient for initial combat use.
This work combined with that of the Army’s pilot plant at Radford provided the technical “know how” necessary for the construction and operation of the full-scale production plants that followed later.
During 1943 additional dry-extrusion facilities were built and installed by the Services—the Navy at its Indianhead Powder Factory and the Army at its Radford Ordnance Works operated by the Hercules Powder Co.
The Russians, having lost many of their industrial facilities to the German armies, needed dry-extruded powder for their rockets. To meet the Russian procurement schedules, a huge dry-extrusion plant, the Sunflower Ordnance Works, was designed and built by the Hercules Powder Co. under contract with the Ordnance Department. By the time the Russian orders had been filled, this plant was available to meet, in part, the huge demands of our own Services during 1944 and 1945. Other plants for producing dry-extruded rocket grains were in operation or under construction by the end of the war. From the very beginning Army Ordnance powder plants supplied millions of pounds of sheet ballistite to feed all the extrusion plants.

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4. Rocket Versus Submarine

MOUSETRAPPING THE U-BOAT

The methods and weapons which the Allies used to meet and defeat the Axis submarines were among the closely guarded secrets of the war.
In late June 1942, a telegram filed at Key West, Fla., undoubtedly puzzled the operator. The message, addressed to the Director of the California Institute group, read something like this: “Mousetraps ariving on schedule. Minnie Mouse urgently needed.”
To the initiated, this crytic language was perfectly clear. It meant that the Institute rocketeers were well along on pilot production and delivery of the rocket-propelled antisubmarine bomb—first of the United States rockets to be fired against the enemy and a weapon that was still hurling death at the Axis when hostilities ceased.

U. S. S. “Greer” Attacked

The United States was drawn into the submarine war at a rate faster than we were able to prepare against it. Self-preservation demanded that we support British resistance. The 4 September 1941 submarine attack on the United States destroyer Greer, on patrol duty south of Iceland, pitched us into the war in the Atlantic. From then on, our warships were ordered to answer any interference with gunfire.

New Weapons Needed

The conventional type of antisubmarine attack, originated in World War I, depended on depth charges or “ash cans” which were dropped successively to form a pattern to blanket the area where a submarine had submerged or was suspected to be. The depth charge attack required time for a surface vessel to get over the right spot and then maneuver to complete an effective pattern. Many kills of German U-boats were claimed in World War I, but the postwar audit showed less than a third of them valid.
The need was for projectiles which could be propelled ahead of the attacking ship in an instantaneous pattern, while sound contact was maintained without interruption.

British “Hedgehog”

The British had already tackled the problem, and found a solution— the “hedgehog,” with which bombs could be fired ahead of a ship. The device worked effectively, but it worked on the principle of the mortar, and the recoil was on the order of 14 to 50 tons in ripple salvo firing. The hedgehog therefore could not be fired from ships smaller than a destroyer.

Cocked for the kill are these “Mousetrap” rocket bombs, seen here in the launchers of a PC boat ready for the Nazi submarine hunt in the Caribbean {BuAl^Ol).

The Caltech-NDRC group began work in the fall of 1941 to develop the recoil-free rocket into a similar antisubmarine weapon for smaller patrol craft.
As in the case of so many other rocket projects, lack of a proper propellant and means to produce it in quantity, was the first barrier to progress. A press for dry-extrusion of grains up to 2.5 inches in diameter was ready in January 1942, but it was not until February that a reasonably adequate supply of sheet ballistite was provided for processing.
Bombs patterned after the “hedgehog” bombs, but equipped with rocket motors, were made ready, and the first sea-firing tests took place on 30 March 1942 off San Diego. The launcher consisted of channeled rails, fanned out slightly from parallel, so that from rails elevated at an angle of 45°, the bombs would fall ahead of the ship in a line at right angles to the ship’s course. The development of the mousetrap passed through the usual series of growing pains—difficulties with powder, with launchers, with fuzes.
Trials led to the standardization of four-rail launchers and later of eight-rail launchers, pairs being mounted one on each side of the forepart of the vessel. The projectile was equipped with a fuze which would “arm” by hydrostatic pressure and then detonate only on contact with a solid object under water.
The appearance of the rails when raised for firing reminded someone of the familiar kitchen killer cocked ready to kill, and so the name of “mousetrap” was born. The miniature mousetrap rocket developed later for training use was inevitably christened “Minnie Mouse.”
Reporting on a test of dummy bombs against an American submarine on 17 April 1942, off Key West, the Commander, Service Squadron Nine declared: “* * * it is strongly recommended that all ships of PC Division Thirty-one and the Coast Guard cutters now assigned to this command be equipped with this armament as soon as possible.”
Four days later, the Vice Chief of Naval Operations requested the Bureau of Ordnance to furnish mousetrap equipment for all 110-foot subchasers and all Coast Guard vessels of 83 feet and up which could not take the hedgehog. To save time, the Bureau requested that the facilities used by C___for the production of experimental models be employed for rush production in larger quantities for immediate use against the German subs.

Full Speed Ahead

Quantity production was not one of the purposes for which NDRC was set up. But the submarine situation would not wait. The threat of enemy submarine attack was no longer something remote. It had come so close that Atlantic coastwise shipping was under attack. There was urgent need for any weapon that promised to save American lives and American shipping. NDRC and the California Institute group acceded to the Navy’s “crash” production request.

The Mousetrap Goes to War

By early October 1942 100 mousetrap installations had been completed on ships ranging from destroyer escorts down to small harborpatrol vessels. These ships took up their share of active patrol work

along the Atlantic Coast and in the Caribbean, and 6 months later vessels equipped with mousetrap installations were busily engaged in the Pacific.
Against enemy submarines the mousetrap maintained a goodly percentage of kills. A hit with a mousetrap projectile might or might not sink the submarine, but in any case it almost surely ruptured the pressure hull, forcing the submarine to come to the surface where it could be destroyed by more conventional means.
The mousetrap proved an excellent complement to the depth-charge attack. Combined, the two methods of attack resulted in a considerable gain in effectiveness and a great saving in depth charges.

The Survivors Were Picked Up
Combat reports, for example, tell how on 17 April 1943 in the Atlantic two Coast Guard vessels got a submarine contact. They made a depth bomb attack, then a second, then a mousetrap attack. Eleven minutes later, the sub surfaced, moving slowly ahead at about 2 knots. She was down by the stern as though damaged. The Coast Guard ships opened with their guns and the sub sank. The survivors were picked up.
On 24 March 1944, in the Pacific, two destroyers, a destroyer escort and a patrol boat made contact with a Japanese submarine. They attacked with both depth charges and mousetrap rockets. Detonations, indicating hits, were heard following the last mousetrap attack, and later a large oil slick appeared. A “probable” went down in the records.

THE ROCKET THAT FIRED BACKWARD

The development of air-borne antisubmarine rockets literally began backward.
The airplane had proved to be a potent weapon in the war against the U-boats. Patrolling aircraft ranged far and wide over the sea lanes in a ceaseless search, but in the early years of the war, although many submarines were discovered and attacked with guns and bombs, the percentage of “sure kills” was disappointingly low. Improved antisubmarine armament for aircraft was badly needed.
In many attacks against submarines there were occasions when the airplane passed directly over the submarine. A bomb that fell vertically would be useful in such situations. Ordinary bombs and depth charges had to be aimed and dropped well short of the target because they continued to travel forward after dropping from the moving aircraft.
The formula for a weapon to do the trick of falling vertically from a fast-flying airplane resulted from discussions between the NDRC scientists working on antisubmarine problems and the rocket workers at Caltech. Forget for a moment, they said in effect, the usual concept of a rocket as something to be fired forward at high speed. Instead, fire it backward from an airplane at exactly the plane’s forward speed. The two velocities will cancel one another out, and the effect will be to release a projectile which will plummet down to a target directly beneath. The suggestion was quickly tried. It worked. As finally

perfected, the retro-firing bombs popped from launching rails mounted beneath the airplane wings, stopped in midair, and fell vertically to the target.
For these retro-rockets, modified “mousetrap” heads were used, each carrying 35 pounds of high explosive and a special contact-firing fuze. In order to match the different flying speeds of various antisubmarine patrol aircraft, three special rocket motors were developed, so that projectiles having three different rearward speeds were available.
When this project was assigned to the CIT laboratories, the Navy instructed the Commander, Fleet Air West Coast to collaborate with and help the laboratory, to expedite development in every possible way. This cooperative endeavor worked extremely well and was to continue through most of the subsequent aircraft rocket development for the Navy.

First American Rocket Fired in the Air
On 3 July 1942 retro-bombs were first test-fired successfully from a Catalina (PBY5A). It was the first firing of an American rocket from a plane in flight.
Launchers of bent steel were constructed for the PBY installation, 12 rails on each wing. Later, dural rail launchers were designed for the TBF Avenger.
In addition to the retro-bomb, a backward-firing rocket flare or retro-float light was devised. This float light proved most useful to the pilots enabling them to mark on the surface the position of a submerged submarine before attacking with a barrage of retro-bombs.
Navy Squadron VPB-63 was the first to be equipped and trained for retro-bombing.
The retro-bomb technique was most effective in restricted waters which could be kept under constant close surveillance, thus compelling any intruding U-boat to travel submerged. In narrow waters like the Straits of Gibralter, where a tight patrol barrier could be maintained to spot enemy subs trying to slip by under water, the retro-bomb proved a valuable adjunct to the depth charge. For example:
Planes 14 and 15 of Squadron VPB-63, were on patrol over the Straits of Gibraltar on 24 February 1944 when Plane 15 made contact with a U-boat and immediately fired a float light. Plane 14 joined in the hunt. A British destroyer appeared, but was requested to go away and not mess things up. After about 20 minutes, Plane 15 regained contact and made its run at 109 knots firing 23 retro-bombs from an altitude of 100 feet. Explosions of some of the bombs indicated they had found their target. Plane 14 fired 24 bombs from 150 feet. The destroyer reappeared and dropped 10 depth charges. Five minutes later, the bow of the U-boat broke the surface, then sank again. A second destroyer joined up and the two destroyers dropped more depth charges. Again the submarine surfaced and its crew began to abandon ship. The destroyers opened fire. A PBY of another squadron came up and dropped depth charges, obtaining a straddle. An RAF Catalina joined in and also got a depth bomb straddle. The bow of the sub rose in its death agony to an angle of 40°, then for the last time slid beneath the surface.
There were other kills—some sure, some probables.

One Last Word
The retro-bomb was to be over-shadowed by the forward-firing aircraft rocket. But it was to have one final word. In the last few months before their surrender, the Germans undertook submerged attacks against Allied shipping in the English Channel and other French coastal waters. Navy Squadron VPB-63, went back to its old weapon. Its planes attacked a German submarine in the Bay of Biscay on 30 April 1945. The attack went down in the official records as a “B,” meaning that the submarine was probably sunk. It was the last German submarine reported sunk during the war.

FORWARD-FIRING ROCKETS HIT THE SUB

The first submarine kill in which American forward fired aircraft rockets were used was made in the Atlantic on 11 January 1944. Two carrier-based TBF’s surprised a German U-boat on the surface. They began the attack with a rocket-firing run, the second plane getting two probable and two certain hits. Then they made a second run to drop depth bombs, and one of the planes got a perfect straddle. Since the U-boat was still surfaced and circling slowly, one plane bored in again to machine-gun the flak gun crews. As the second plane followed, the U-boat began to submerge, and the second plane dropped depth charges squarely over it just as the conning tower went under. Shortly afterward, the U-boat emerged with its bow up at a 50° angle, then settled level in the water and began to circle slowly again. Then bow and stern began bobbing up and down alternately.. Soon it went dead in the water, and a large puff of smoke blew out of it, apparently from an internal explosion. Immediately afterward it sank stern first, for good.
The rockets used by these planes were 3.5 inch diameter rounds with 20-pound solid steel heads, designed by the California Institute of Technology group for antisubmarine warfare.

British Experience
Forward-firing aircraft rockets were a natural evolution in the rocket program. The British were the first to develop and demonstrate the 3.5-inch forward-firing aircraft rocket as an antisubmarine weapon. Tests conducted against a grounded destroyer off the British coast indicated that these rockets had a long, shallow underwater trajectory, and after 50 feet of under-water travel still retained sufficient velocity to penetrate submarine hulls. An under-water hit of this kind would either sink the sub or force it to the surface, where it could then be destroyed by conventional methods.
The most usual experience in making a contact while hunting submarines with aircraft was for the plane’s radar to pick up a U-boat at night with at least the sub’s conning-tower exposed, so that it could run its Diesels to charge its batteries. Discovered, the sub would probably crash dive. The aircraft rocket offered hope of developing a weapon with which a quick blow could be delivered under water, either just before or just after the sub’s conning-tower disappeared.

Top-Priority Project
Reports began to come in from a British squadron of patrol planes operating in the Mediterranean. Using forward-firing rockets, they had obtained several kills against submarines. Spurred by this encouraging news, the Caltech group in the early spring of 1943 made the development of forward-firing aircraft rockets a top-priority project. It was proposed that the first objective should be a rocket for use both against submarines and surface ships, but the possibilities of developing such a rocket further, equipping it with a high explosive head effective against a variety of targets on land, were already foreseen.
The 3.5-inch rocket which resulted from this program was pin-stabilized and had an over-all length of 54^ inches. The propellant consisted of a single grain of dry extruded ballistite weighing 8% pounds. The total weight was 54 pounds and the velocity was 1,175 feet per second. The rockets were launched from rails mounted under the wings of the airplane. These finned rockets proved exceedingly accurate because, being carried through the air at high speed, they were already stabilized at the moment of launching.

A Strenuous Schedule
It was soon recognized that the forward-firing aircraft-rocket program would have to meet a strenuous schedule which would overtax the small experimental unit of the Navy’s Fleet Air Wing 14 which had been doing the actual test firing from aircraft for CIT, first for the retro-bomb and later for the forward-firing rocket. It was also realized that a sizable test area would be required for the ensuing experiments. It was at this time, therefore, that the site in the Mojave Desert near Inyokern was selected, which is now known as the Naval Ordnance Test Station. At approximately the same time the personnel of Fleet Air Wing 14 became a nucleus around which Aviation Ordance Development Unit I was formed. This unit was slated for transfer to Inyokern as soon as the necessary facilities were available.
The tests of the 3.5-inch rocket on various types of patrol and combat planes were most successful. Both the Bureau of Ordnance and the facilities available to the California Institute broke all previous records for quantity production of the new weapon. Many times production was under way before final drawings were completed.

Under-water Travel
For antisubmarine work a study was made of the head shape in relation to under-water ballistics, and as a result, a new head-shape was developed which doubled the lethal under-water range of the rocket. The new head was immediately put into production and service.

As destroyers of enemy morale, aircraft rockets occupied a place higher on the list than, perhaps, their actual destructiveness warranted.

History of Aircraft Rocket Development
As in the case of so many other weapons, the onset of World War II found the United States woefully backward in the race to perfect aircraft rockets. Britain and Russia were well ahead of us. As early as 1942, pilots of the Soviet air force, first to use aircraft rockets, were firing rockets at ground targets, particularly tanks.
Thanks to the help of American science and industry, the United States was to end up as the foremost designer, producer, and exploiter-of military aircraft rockets. But we started at best a poor fourth— and our success owed much, as in other things, to the better prepared British.
The Germans in the summer of 1943—several months before an American aircraft rocket was fired in combat—demonstrated rockets as a formidable weapon of plane-to-plane warfare in the air. Using converted ground rockets, the Luftwaffe launched fleets of rocketcarrying fighters against our then unescorted bomber formations over Germany.
The Luftwaffe's rocket tactics were uncomfortably successful, especially during and immediately after the period of the Schweinfurt raids. It was not until the AAF was able to increase the range of our fighter planes so that they could provide cover for the bombers that the menace was effectively countered. Slowed by the drag of the rocket-launcher installation, the rocket-carrying planes of the enemy were a fairly easy mark for our unhampered escort fighters.
Meanwhile, the British were using their antisubmarine aircraft rocket against surface ships as well as U-boats. It was volleys of these rockets which destroyed the Italians’ prized liner Rex.

U. S. DEVELOPMENT PROGRAM

First American Aircraft Rocket
In 1918, while working with Dr. Goddard at the Ordnance Department’s Aberdeen Proving Ground, Dr. Hickman proposed 4-inch diameter rockets to be fired from tubes under airplane wings. These rockets included high explosivet-filled burster tubes for fragmenting the motors in addition to the heads, to increase lethal effect. With the ending of World War I, the project was left in the idea stage.
In 1940-41, the destruction of German bomber formations was the primary defensive problem facing the Allied Air Forces.. NDRC had initiated the development of proximity fuzes—a device which

Top illustration shows a test of the “Tiny Tim" by means of a ground firing of the big rocket from a static plane; objective is to measure the blast effect on the plane's structure. At bottom is a demonstration of a “ripple" when ten 5-inch LIV AR rockets are fired in a string, or ripple fire, at 1,800 feet a second from an Army Thunderbolt. Ten rockets carry 1,080 pounds of metal and 80 pounds of explosive (Top, BUA 189941; Bottom, AAF Dover}.

5. Rocket Armament for Aircraft

“TINY TIM”-—A REALLY BIG ROCKET

When the scientists of NDRC and their Navy colleagues produced “Tiny Tim,” latest and biggest American aircraft rocket, it was as if they had put wings on a pair of 12-inch guns and lengthened the guns’ range to that of a medium bomber.
This giant rocket was the culminating achievement, as the war ended, of a program of aircraft rocket development which gave the American fighter plane the ability to hurl at an enemy target more high-explosive than is carried in a salvo from a light cruiser.
“Tiny Tim” was science’s answer to the fighting services’ demand for “a really big rocket.”
Here, first told publicly, are his vital statistics:
“Tiny Tim’s” overall length is 10 feet 3 inches, his diameter only a quarter-inch less than a foot. His weight is 1,284 pounds.
“Tiny Tim’s” usual head, one of several, is a semi-armor-piercing bomb with a total weight of 590 pounds, of which 150 pounds is an explosive charge of TNT. A charge of 146 pounds of powder drives him through the air. Though his development Ws not completed until shortly before the end of hostilities, “Tiny Tim” was on hand to hit the Jap on Okinawa.

ROLE OF AIRCRAFT ROCKETS

From early in 1944, on through the remainder of the war, forwardfiring aircraft rockets played a significant and increasingly important part. First used in Burma, aircraft rockets later did their bit in the Normandy invasion and the advance across France and into Germany, in the Mediterranean theater and the invasion of southern France, they went to the Pacific where they really came into their own in the Saipan-Tinian-Guam operations and those that followed.
Aircraft rockets were a valued supplement to the bombs, machineguns, and cannon of the military airplane. Rockets are more accurate than bombs, but weight for weight do less widespread damage. Rockets are less accurate than machine-guns and cannon, but pack a bigger punch.
The recoil of the 75-mm. cannon mounted in the nose of the B-25 medium bomber subjects the plane to an abrupt shock that requires substantial strengthening of the plane’s structure. But aircraft rock-ets of even larger caliber and greater explosive loads can be fired from a fighter plane without affecting its flight.

Targets
Aircraft rockets were especially effective against warships up to destroyers in size and against smaller cargo, transport, and escort ships, or against large warships to silence their antiaircraft batteries.
In attacks on enemy airfields, rockets were particularly useful to destroy radios and radar installations and smaller buildings, parked planes, and fuel dumps.
Aircraft rockets were valuable in attacks on tanks, light guns, concrete pillboxes, and locomotives.

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would explode a projectile when it passed near an enemy airplane. The combination of such fuzes with aircraft rockets looked very promising as fighter armament for the attack of bomber formations. Starting in early 1941, Colonel (then Captain) Skinner, and later other Ordnance Department officers, working with Navy and Section H personnel and facilities at Indian Head, developed such an aircraft rocket, first test-fired on the ground on 29 May 1941. Out of this grew the 38-pound 4.5-inch M8 rocket carrying about 5 pounds of high explosive. This rocket used a charge of 30 grains of solvent extruded powder mounted on a cage type trap. Fixed fins were used on early models. These were replaced by folding fins so that 4.5-inch tubes could be used as launchers.
Captain (now Colonel) Harry L. Donicht of the AAF Wright Field Armament Laboratory was assigned to supervise adaptation of rockets to AAF aircraft. The AAF developed a three-tube cluster launcher and mounted one cluster under each wing of a plane. The first forward firing of an American rocket from a plane in flight took place at Aberdeen on 6 July 1942, when an Army fighter fired 4.5-inch folding fin rockets from these launchers.
Ordnance, AAF, and Section H carried forward with development, testing, improvement, production, and distribution. Many unforeseen technical difficulties delayed the project. The final model, T-22, operated satisfactorily over a wide range of temperatures. Meanwhile the importance of the plane-to-plane rocket had diminished as the enemy bombers had been driven from the skies. Attention was therefore shifted to the use of rockets against ground targets. In the winter of 1943-44 AAF planes fired M8’s from cluster launchers in attacks on Japanese ground installations in Burma—the first combat use of American aircraft rockets.

California Institute Developments
Caltech began its development of forward-firing aircraft rockets in the spring of 1943; its first weapon being the 3.5-inch antisubmarine rocket which was equipped with a 3.25-inch motor. Introduced in combat against German submarines in January 1944, this rocket, with its long shallow underwater trajectory, was found useful for holing cargo ships below the waterline—the most effective method of sinking ships.
When a 5-inch 50-pound explosive shell was modified to serve as a head for this rocket, in place of the 3.5-inch 20-pound solid head, another weapon was added to our arsenal. Naval airmen found this 5-inch aircraft rocket effective against many ground installations and against, antiaircraft guns and for silencing the antiaircraft batteries of enemy warships.

Launchers
The first aircraft rocket-launching device evolved by the CIT group—a set of eight slotted rails mounted four under each wing— created a serious drag on the plane. The original 6-foot rails were shortened—without material effect on accuracy. The next logical step was the zero-length launcher, consisting meerly of two posts for each rocket, attached to the under side of the wing. Lugs attached to

Plans for “Tiny Tim”
For some time, the rocketeers had been considering plans for “a really big rocket” which would meet certain tactical requirements. The progress of the war revealed an even more pressing need for a rocket of giant size.
As the Allied forces fought their way closer to the Japanese homeland, they were finding the enemy even more strongly entrenched. Observers who had watched the destruction wrought by the rockets so far used in service believed that a larger more powerful rocket would be most effective in blasting the Jap out of his pillboxes and bunkers. It would be useful, too, in firing at larger enemy ships.
At a meeting on 24 February 1944 members of the CIT group agreed on preliminary specifications—a motor tube approximately 12 inches in diameter, a propellant charge of four dry-extruded ballistite grains each weighing some 40 pounds, and a tQtal weight for the completed rocket of approximately 1,200 pounds. By late April a complete round was fired. By that time, the giant rocket was known by the affectionate diminutive of “Tiny Tim.”

Drop Launching
The size and tremendous blast of the rocket made the problem of aircraft launching one that required months of planning, building, and testing before the final and successful method was decided on— that of drop launching, using a lanyard to ignite the propellant when the rocket had fallen to a safe distance below the plane. Tests showed that rockets could be so launched with gratifying accuracy.
Also, drop-launching simplified installation of rockets on the plane. With minor adjustments, “Tiny Tim” could be hung on a conventional bomb rack. Thence it could be released by the bomb release mechanism. When it had fallen a few feet below the plane, the lanyard—its upper end fixed to the plane—closed switches igniting the propellant, and “Tiny Tim” was on his way.

Fatal Accident Delays Development
In August 1944 air firing of “Tiny Tim” was interrupted by the crash of the test plane. The pilot was killed and the plane demolished by a nose dive from 1,500 feet immediately after the firing of a round. Investigation showed that the shock wave created by the combustion of the 1,200 grains of black powder used as an igniter had torn loose an elevator trim tab and jammed it in a position that caused the dive. Air firings, with a lighter igniter charge and an increased drop, were resumed in late September.
Finally, squadrons equipped for firing “Tiny Tim” sailed for the Pacific on the carriers Franklin and Intrepid,. The Franklin was struck by a Japanese dive bomber before its planes could fire “Tiny

The power packed by this AAF light A-26 bomber, pictured at the top, consists of 14 rockets in addition to the power of its guns; the combination makes it one of the world's more formidable attack planes. Wings of the Navy, below, are rocket armed as these planes prepare to take off on a battle mission in the Pacific (Top, AAF Dover 883a}; (Bottom, Navy £46959}.

bands encircling the rocket fitted into slotted plates on the bottoms of the posts. Again, the accuracy of rockets fired from the faster planes was little affected, and the drag was so much lessened that even fighter planes had their top speed reduced by only 6 to 9 miles per hour. The zero-length launcher went into service use in the spring of 1944. _
During that year Section H, Army Prdnance, and Air Forces worked together to exploit the advantages of the “zero” length launcher for M8 rockets already in field supply dumps. The clusters of launching tubes were eliminated. Field conversion kits were devised, consisting of a set of large fins and lug bands to be added to rockets in the field, and simple adapter rails to be mounted on zero length launcher posts. These modifications reduced drag and improved the accuracy of the weapon.

Birth of “Holy Moses”
Next goal of the Institute group was a 5-inch rocket with higher velocity than that obtainable through use of the 3.25-inch motor.
By December 1943 the Institute propellant workers had produced a 4.2-inch diameter ballistite grain weighing 24 pounds. The 5-inch motor incorporating this grain was given a safety feature by providing the motor with eight peripheral nozzles for propulsion, and a central nozzle, the primary function of which was to serve as a safety valve. The central nozzle was closed by a disk which held at ordinary atmospheric temperatures but blew out when operation at high temperatures raised the pressure dangerously near the motor’s bursting point.
The new rocket was officially designated the 5-inch HVAR (High Velocity Aircraft Rocket), but the vigor of its blast quickly won it the respectful title of “Holy Moses.” “Holy Moses” was 6 feet long, weighed 140 pounds, and boasted a velocity of 1,375 feet per second or 200 feet per second faster than the 3.5-inch rocket. “Holy Moses” went into combat use in July of 1944.

The “Super” 4.5-inch Rocket
Meanwhile Section H had been developing a somewhat similar 4.5-inch rocket using a new solvent process propellant superior to any other known smokeless powder in its behavior at extreme temperatures. This rocket was developed to meet the demands of the Air Forces for higher velocity and better accuracy than the M8, especially for use against moving targets at greater, ranges.
The answer was the “super” 4.5-inch round, later known as the 115-mm. aircraft rocket. Its production design was established in December 1944. Procurement was initiated by Army Ordnance, but the war ended before this round could be used in combat. It was 6 feet long, weighed 103 pounds, of which 40 pounds was payload and had a velocity of approximately 1,000 feet per second relative to the aircraft launching it. It was stabilized by four large fixed fins. The semi-armor-piercing head of one model was capable of piercing 5 inches of homogeneous armor plate, while the fragmentation head of a companion model contained 8.5 pounds of explosive or nearly twice the amount of HE carried by the early M8.

Tims” in action. But the planes of the Intrepid did launch “Tiny Tims” against the enemy on Okinawa. Unfortunately, the results could not be accurately assessed. There were, it seems, so many things being thrown at the Japs on Okinawa that it was impossible to distinguish the wreckage caused by “Tiny Tim” from the general destruction.

AIRCRAFT ROCKETS WRITE COMBAT HISTORY

“Tiny Tim” wrote the last chapter of a combat record that took aircraft rockets into war theaters around the globe.
Aircraft rockets were first fired from American planes in combat by the Army Air Force in Burma early in 1944. In one period, Tenth Air Force B-25’s, with M-8’s carried in tubular cluster launchers, scored a gratifying total of 55 hits out of 99 rockets fired on 9 missions against rolling stock, supply dumps, and buildings.
In Europe, Army airmen used similar rockets to attack German industrial centers, transportation, and defensive installations from bases in England and Italy for several months before and after D-day, 6 June 1944.
The 5-inch HVAR was first tried out by enthusiastic Ninth Air Force pilots against the railroad yards of Paris on what was officially scheduled as a safe practice run somewhere in England.

D-day, Thunderbolts and HVAR’s
Shortly after D-day a few Thunderbolt fighter planes were equipped with 8 HVAR rockets apiece. They were especially effective, in supporting the break-through at St. Lou. One or two Thv/nderbolts hovered constantly over the smashing, advancing tanks of the Third Army and attacked German heavy tanks and 88-mm. antitank guns when they theatened to hold up the American advance.
During this period the California Institute worked feverishly to produce the rockets which were ferried by air at the rate of 100 per day from California to the Atlantic Coast to European airfields where the P-47’s_were waiting to be armed and take off. It was an inspiring example of teamwork—civilian scientists, Navy developers and testers of the HVAR’s, and Army flyers to carry-them against the enemy.
Col. H. L. Donicht of the AAF, Drs. C. C. Lauritsen, and Carl Anderson of the CIT group, and Group Captain H. W. Dean of the RAF had flown to England on a special mission to supervise the installation of the HVAR’s on the Thunderbolts of the 513th Fighter Squadron (SE) of the 406th Fighter Group.
Numerous attacks were made early in July on tanks, locomotives, rail yards, bridges, and airfields, and spectacular results were attained. The P-47 group scored hits on some of the heaviest German tanks, knocking them out of action, thus aiding our ground forces to move forward.

P-47's Attack
On 17 July, 12 aircraft, carrying four rockets each, attacked the rail yard at Tiger-Quail. A direct hit was made on a flak tower on the first run, silencing it. In subsequent runs 25 locomotives were damaged, also three repair shops and a round house. On the following

day 12 aircraft attacked the airfields at Coulommiers. Thirty-seven rockets were launched at 1,000-yard range from a 30° dive. One large hanger, four small hangars were hit, an Me-110 and a fuel dump destroyed. Later a rocket was fired from 800 yards at 2 staff cars, passing through the first and exploding in the second. A rail bridge at Montford was claimed destroyed by 7 rockets.
On 25 and 26 July a total of 64 rocket sorties were flown, destroying 12 tanks, damaging 13, scoring many near misses, and destroying 3 and damaging 3 other vehicles. From then on these rockets were continuously employed by the AAF in the European theater, with devastating results.

Morale Busters
As more and more installations and rockets reached the forward lines, the effectiveness of the HVAR became more apparent. In addition to the actual damage inflicted on enemy material, the personnel of the German ground forces had such a tremendous respect for this new weapon that upon the approach of a rocket-bearing aircraft, it was reported, they would frequently leave their vehicles and guns in headlong flight for the security of foxholes and other hideouts.
P-47’s firing 5-inch high velocity aircraft rockets also were used extensively in helping to turn back the German counteroffensive in August.
That the results achieved by this squadron were impressive is proved by the Ninth Air Force’s decision to equip all its P-47 aircraft for firing 5-inch HVAR’s. In a letter of commendation written to NDRC, Ma j. Gen. B. E. Meyers stated that this initial use of HVAR’s proved “without question the effectiveness and efficiency of this equipment in actual combat, and has resulted in providing the Army Air Forces with the best antitank weapon of the war.”

Navy Rocket Planes
In the landing operations in southern France and the initial stages of the invasion, the Navy provided the invasion troops with air support by carrier-based F6Fs. These planes fired 693 rockets during the period 15 to 29 August 1944. The F6Fs were credited with playing a large part in the demoralization of German transport; they finally ceased operations only because the rapidity of the German retreat whisked their targets out of range.
Except for antisubmarine operations in the Atlantic, however, the Navy’s principal use of aircraft rockets was in the Pacific.

A First for the Marines
It was a Marine squadron—VMTB-134, flying TBF’s—which had the distinction of firing the first Navy aircraft rockets at the Japanese, 15 February 1944.
That this squadron carried off the pioneering honors was due to their own enterprise and the ingenuity of a service squadron in locating and installing launchers and securing rockets. The rockets reached the squadron on 8 February 1944. On 15 February, with only 3 days training, the squadron took part in a strike on Rabaul. Despite their lack of experience, they used their rockets with considerable success.

From February 1944 to the end of operations in the Pacific, aircraft rockets were an important weapon. Navy TBF”s and TBM’s fired them in the Marshalls, Palau, New Guinea, Carolines, and Marcus-Wake actions. In the Marianas operation, from 11 June to 1 August, Navy planes fired a total of nearly 5,000 rockets against the enemy. By that time, rocket-firing F6F’s were in action and joined in this first large-scale demonstration of the aircraft rocket as a weapon for close-support work. Aircraft rockets, though in considerably lesser numbers, were used in actions in the western Carolines, 25 to 28 July, and the Marianas and Bonins, 29 July to 3 August.

Blasting Them Out

As a weapon to dislodge the enemy from well-fortified positions, and to support our ground forces, the rocket was used more widely than in any other application and was ideally suited to its task. When our forces landed on Saipan, Guam, Tinian, Iwo Jima, and Okinawa, they found the Jap burrowed in caves, block-houses, and pillboxes. These were artfully camouflaged and difficult to detect, so well protected that only direct hits were effective, and well defended by antiaircraft guns. Aircraft rockets with their accuracy and penetrating power proved superior to bombs against such targets. Effective and close liaison was set up between the ground forces and the carrier forces supporting them. Wave after wave of rocket-equipped fighters flew in at low altitude sending their rockets into the heretofore invulnerable Japanese positions that were taking such a toll of our advancing ground forces.
Dive bombers screaming down in nearly perpendicular dives silenced gun positions with their rockets, allowing them to release their bombs at low altitude safely and demolish the target with the heavier destructive power of the bomb.
The ground forces soon learned the value of the aircraft rocket and the rocket planes wrere called upon whenever tough obstacles presented themselves in their path. An air coordinator, armed with rockets with smoke heads, was kept over the target continuously during the duration of the strike. Radio contact with the ground forces indicated the targets which were giving them the most trouble and which they wanted wiped out. The air coordinator marshalled his rocket planes, made an approach with smoke-head rockets to indicate the exact target, and left the rest to the planes armed with rockets with high explosive heads.

“Well Done”

The result usually was a “Well done—Thanks!” from the ground forcés and a subsequent advance made a great deal easier by the destructive damage of the aircraft rocket.

Cause—AAF P-lfl Thunderbolt, top, armed with HVAR's like those used so tellingly in the Normandy invasion. Effect—German Mark V tank, below, killed by Thunderbolts du/ring the St. Lo, France, break-through, in July 19 kl; first crippled by the plane’s HVAR^s, the tank was finished off by the .50 caliber gu/ns of the P^Ts (Top, AAF HVAR; bottom, AAF

6. Rockets for Amphibious ^^arfare

THE CRUCIAL INTERVAL

Fired from American landing and support craft in the amphibious operations of World War II, barrage rockets saved thousands of American lives. In the Pacific, they were one of the factors which caused the Japanese enemy to change the pattern of his resistance to American landings. With barrage rockets, American commanders were able to drench landing beaches for considerable distances inland. Barrage rockets helped give assaulting soldiers and marines the fighting chance they needed to win a toe-hold without that bloody slaughter in the surf and on the sands which made American leaders, after Tarawa, wonder how we could continue to pay the human cost of island conquest.
It became grimly plain, as American forces fought their way from island to island, from landing to landing, in the Pacific that the crucial phase in amphibious operations is that interval between the moment the naval and air bombardment must be moved inland and the time the first assault waves hit the beach. It is that interval which gives the beach defenders the chance—as at Tarawa—to organize and pour a murderous fire into the landing forces.

Firepower for Landing Craft
The barrage rocket answered the vital question posed by that interval. It enabled small craft, for the comparatively short period of the actual landings, to strike with the hitting power of destroyers against enemy strongpoints within small-arms range of the landing beaches. Before the close of the war, the enemy had paid final tribute to the effectiveness of the barrage rocket. The Japanese first line of defense—as at Okinawa—was pulled back from the beaches out of rocket range. Soldiers and marines came ashore against astonishingly light opposition—only it was not astonishing. The barrage rocket had imposed its powerful logic on enemy tactics.

ACTION OF OKINAWA

In the last great amphibious operation in the Pacific, the conquest of Okinawa, rockets really came into their own. Here were combined to a degree never before realized the use of rockets on land, from the air, and from the sea.

Okinawa Rocket Fleet
A flotilla of 12 rocket ships went into action at Okinawa on 26 March 1945, and for the next 12 weeks poured ashore in support of land operations a total of more than 30,000 rockets.

Barrage Rockets—The latest type of barrage rocket ship, the LSM{R}, firing 5-inch spin-stabilized rockets from automatic firing, remote-controlled launchers. These fire at the rate of 300 rounds a minute (BuA 186033).

The rocket ships supported the landings on Aka Shima, joined in the bombardment of Aware. They attacked the town of Takashippo on Okinawa, helped neutralize enemy infantry and mortar concentrations until a beachhead could be secured. They participated in the bombardment of Ie Shima and had an important part in backing up the landings there. They helped the ground troops to win the eventual break-through of the enemy’s Naha-Shuri-Yonabaru defense line. They supported the landings on Iheya Shima and Aguni Shima.
In the closing days of the Okinawa campaign, four ships of the rocket fleet were assigned to the Tenth Army Artillery section. Directed by artillery aircraft observers, the rocket ships loosed day and night bombardment fire against last-stand Japanese troop concentrations.
It is noteworthy that, while eight of these rocket ships were equipped for firing improved, fin-type rockets, four of them wefe fitted to fire spin-stabilized rockets—representing a development in rocket design of major importance. These four ships, each with an installation of 85 automatic launchers, could get off a salvo of 1,020 5-inch rockets in approximately 1 minute.

Super-Rocket Ships
The part played by the rocket ships at Okinawa concluded the combat story of ship-borne rockets in World War II, but it is not all of the story. For, good as the rocket ships were, they were hurriedly contrived interim vessels. On their way across the Pacific when the Japanese sued for an end to hostilities were more examples of the surprise weapons which never had a chance to hit the enemy. These were the first of 48 super-rocket ships planned by the Navy. These LSM(R)’s pack an even greater punch than the ships that fought at Okinawa. Each ship carries 40 mm. and four 20 mm. twin mounts, four 4.2-inch chemical mortars, a 5-inch dual-purpose gun, and 10 rocket launchers, continuously fed and automatically fired, and aimed by remote control, each capable of firing 30 spin-stabilized rockets per minute, or 300 rockets per minute per ship.

BARRAGE ROCKET DEVELOPMENT

Behind the drama of combat is the story of the patient—and sometimes frenzied—efforts that made the fighting record possible. It is a story of officers and men of the Navy and scientists and other workers of NDRC’s California Institute group. It is the story of research work which started by designing a barrage rocket with a range of 1,100 yards, then adapted the 5-inch aircraft rocket to barrage use, and lastly developed a whole series of spin-stabilized rockets with ranges up to 10,000 yards.

End of the War’s Defensive Phase
By the summer of 1942, the defensive phase of the war had ended. The invasion of North Africa was being planned, and so were the island hopping operations in the Pacific. It was obvious that the next great battles would commence as amphibious actions.
It was Vice Admiral Wilson Brown, then Commander, Amphibious Forces, Pacific Fleet, after attending a demonstration of the mousetrap and other California Institute rockets, who suggested that a

special type of rocket projectile might be the means to supply fire support which could travel right with the assault waves. He proposed a rocket with a range of at least 1,000 yards and a high-fragmentation head, to be fired from launchers suitable for mounting on the landing craft themselves or on accompanying light support vessels.
The California Institute group jumped into the job. A quickly designed head, fabricated from readily available 4.5-inch pipe, packed 6.5 pounds of TNT in its 13-inch length. The mousetrap rocket motor, attached by means of an adapter screwed into the base of the head, provided 10 percent more range than the 1,000 yards called for. Less than 10 days after the trials which had brought forth the admiral’s suggestion, models of the new rockets were successfully test fired. Within another month, a 12-round “crate” launcher had been designed, installed on a 37-foot support boat, and sea tests were staged.

Rush Job for NDRC
Suddenly, in August 1942, the center of interest in the new barrage rockets shifted to the East Coast. The Commander, Amphibious Forces, Atlantic Fleet, requested a demonstration. It was staged August 25 in Chesapeake Bay. Four days later, the Navy’s Bureau of Ordnance requested the CIT group to supply for Amphibious Force, Atlantic Fleet, 25 pairs of launchers, 3,000 rounds of rockets, and 3,000 fuses—time of delivery, within 30 days. BuOrd did not hide the fact that the Navy was in a hurry.
Once again, an NDRC research group found itself up to the neck in a production job. They produced. Physicists pitched in as expediters, chemists as straw-bosses, ballistics experts as inspectors. Office workers put the covers on their typewriters—and hiked to the shops to put in overtime on the assembly line. The last of the rockets were completed and flown east just under the deadline.

North Africa
Only 102 days after the first sea tests, on 8 November 1942, those rockets were being fired in support of the landings at Casablanca. From that date on, barrage rockets were used in virtually every landing in the Mediterranean and European theaters—Sicily, Italy, Utah Beach in the Normandy invasion, and the invasion of Southern France.
The California Institute group was called on to meet additional staggering production demands, which they did by establishing a special production section. Thus they were able to fill in the interim until the Navy’s industrial contractors could get production going on a really large scale.

Britain Lends a Hand
Other types of rocket ships were used to cut down Allied losses in landing operations. Following the defeat of the Axis in Africa, the British Royal Navy converted several of its LCT’s to fire rockets and tried them out in the invasion of Sicily, with marked success.
In August 1943, at the Quebec Conference, it was decided that a number of British LCT(R)’s should be turned over to the United States Navy. The British LCT’s were approximately twice the size of the American LCI’s and fired more and bigger rockets. A special group of United States Navy officers and men was established to con

vert the vessels for American use and provide for their incorporation into specialized support groups. For many months the work of reconversion and training went on. The pay-off came on 6 June 1944, when the rocket-firing support groups, both American and British, with Navy shells screeching overhead, moved up to the Normandy beaches and turned them into flaming floors of fire.

Launchers
During 1943, CIT devoted much time to perfecting a series of barrage rocket launchers. A 120-pound launcher was designed for the 2%-ton amphibious truck, the DUKW or “Duck.” Another launcher, lightweight with 10 rails, was developed for the jeep. An 88-round launcher was adopted for the medium landing craft, the LCM.
The most important improvement in launching devices was the 12-round gravity feed launcher. Functioning automatically, it could fire single rounds or loose its full load in less than a minute. It was light in weight and far safer for the operator in that it could be loaded from the side rather than from muzzle or breech. It could be mounted on practically anything—and was—from a jeep to a 2%-ton truck, from the amphibious “Buffalo” tractor to an LSM. By August 1944, the Navy had procured 20,000 of these launchers.

THE JAPS MEET BARRAGE ROCKETS

Following their successful early use in the Mediterranean and ETO, barrage rockets next appeared in the Pacific where the Second Engineer Special Brigade (2d E. S. B.) introduced them to the Japanese. As part of MacArthur’s forces which leap-frogged up the northern coast of New Guina, the 2d E. S. B. did a brilliant bit of work in helping to take Satelberg, a strong point 15 miles from Finschafen. Mounting two of the original support-boat type launchers on a trailer, members of the brigade manhandled them to a mountain emplacement that gave them a direct line of fire on the Jap positions.
On 14 December 1943, the 2d E. S. B. made the first large use of barrage rockets in an amphibious landing in the Pacific when they used their rocket-carrying DUKWs in support of the assault on Arawe on New Britain. For the next 6 months, rocket-equipped landing craft, special rocket gunboats and rocket DUKWs played an important role in nearly every amphibious landing operation in which the 2d E. S. B. participated.

Rocket Ships Standard Equipment
The Seventh Fleet included numerous rocket-equipped landing craft. And through 1944 and 1945, until the long Southwest Pacific campaign culminated in the liberation of the Philippines, the barrage rocket continued to smash the enemy and save American lives.
Rocket ships became standard equipment. And as one amphibious operation followed another, amid the din of battle could be heard the constantly urgent demand for more rockets from more launchers mounted on more and larger ships. First installed in the smaller support boats, rockets progressed from bigger to still bigger ships, until they were mounted on LCI’s (Landing Craft, Infantry) and finally on LSM’s (Landing Ship, Medium).

Prelanding Use
Sometimes, even before landing began, barrage rockets were used to provide cover for the underwater demolition units—the groups then went in ahead of the landing wave to remove underwater obstacles to landing craft. Barrage rockets softened up the beaches for the landings at Biak, Wakde, Pelelieu; they contributed their share to Admiral Spruance’s famous “Kwaj alein haircut.” They were used at Guam and Saipan and Tinian. In the recovery of the Philippines they plastered the beach objectives at Leyte and Ormoc Bay and Lingayen Gulf.
As the effectiveness of barrage rocket fire became more apparent, training and installation programs kept a supply of rocket-trained personnel and rocket-equipped craft moving to the fleets. In the forward areas, rocket installations were worked out on landing craft, and additional training programs were carried on. The best testimony of all to the effectiveness of the barrage rockets was the fact that the landing troops, after seeing the effects of rocket barrages a few times, began requesting to be sent in with the first wave, which hitherto had been considered the most dangerous.

ROCKET-FIRING PT BOATS

Late in 1943, the usefulness of barrage rockets branched off into an additional direction somewhat different from that of supporting landings. It was at that time that the Commander, Motor Torpedo Boat Squadrons/MTBRons), Seventh Fleet, began to investigate the installation of barrage rockets on PT boats—an audacious idea, for more conservative tacticians held that the high dispersion of the rocket made it unsuitable for the sharp-shooting missions the PT boats were expected to carry out. But it was obvious that PT boats could use greater hitting power, so from the 2d E. S. B., MTBRons, Seventh Fleet, obtained the “loan” of 200 barrage rockets and two 12-round crate launchers. The results from the first firings in the Cape Coiselles action were so good that all the PT boats of Squadron Seven were soon rocket-equipped.

Knockouts Wholesale
The first outstanding success of the PT rocket boats was scored in the Aitape landings; they knocked out 107 enemy craft of all varieties.
Soon most of the boats in Squadron Eight were also equipped with launchers; and by the end of the Aitape operation there were one or two PT boats with launchers in every squadron. Eventually some 60 PT’s in MTBRons Seventh Fleet were so equipped.
In addition to providing additional rocket fire in landing operations, PT boats were frequently used to harass enemy coastwise shipping. Off Ormoc, in December 1944, PT’s sank a Japanese lugger about 130 feet long with rockets alone. The PT boats, on patrol along shore, used their rockets against any targets that turned up—enemy trucks, bivouac areas, gun positions, supply dumps, concentrations of Japanese personnel.
By the end of 1944, MTBRons Seventh Fleet were using 2,500 to 3,000 barrage rockets per month.

THE SPINNER FAMILY

So far as World War II is concerned, the final phase in the development of barrage rockets saw the rocket researchers turn from finned rockets to the development of spin-stablized rockets—already mentioned in connection with the Okinawa campaign. Spinners promised greater accuracy than could be obtained with finned rockets and they were more readily handled in the field.
In early experimentation with powder-propelled rockets, German scientists had concentrated first on spin-stabilized types. British and American work on rockets had, by contrast, first exploited the finned types.
Development of American spin-stabilized rockets was undertaken in 1943 by both CIT and Army Ordnance.

Plenty of Action
The first spinner developed by the California Institute group was a 3.5-inch rocket, designed as a possible substitute for the Marines’ 75 mm. pack howitzer. Though it never saw service use, its successor, the 5-inch high velocity spin-stabilized rocket, saw plenty of action.
This 5-inch spinner was designed to provide PT boats with greater firepower. As early as August 1943 reports began coming back from the Pacific that the Japanese were using armored and armed barges to reinforce and supply island garrisons. Against these barges, the PT’s needed heavier armament.
What was called for was a high-velocity rocket which would have good accuracy and good penetration performance in low-angle fire at ranges of from 700 to 1,000 yards. The CIT group, therefore, began the development of a 5-inch spin-stabilized rocket which would have a maximum velocity approximating 1,500 feet per second. Final tests were concluded in the late summer of 1944 and the new rocket went into service use on PT boats in the Pacific early in 1945.
This 5-inch high velocity spinner is fired from twin launchers each with 8 tubes arranged in tiers of 4, 1 above the other. The launchers are mounted forward, 1 on each side of the boat, providing a capacity of 16 rounds without reloading.
Two models of the rocket have been used in service. Each weighs some 50 pounds and is 30 inches long. One model has a semi-armorpiercing head and a velocity of 1,415 feet per second. The other model has a general-purpose or thick-walled head and a velocity of 1,540 feet per second.

Barrage Spinners
While work on the high-velocity spinner was under way, the Navy called for a barrage rocket with a longer range than the 1,100 yards of the 4.5-inch rocket. As happended during the Saipan operation in June 1944, obstacles such as reefs or planted obstructions might

Batteries of bad news for the Japs—A multiple installation of automatic gravity feed launchers firing -5-inch spinner rochets, mounted aboard an LSM(R). The scene is at Aka Shima, Ryukyu Islands (BuA 313668).

keep rocket-firing ships too far off shore for their barrage to reach the target. A 5-inch spinner with a 5,000-yard range seemed to offer the best answer to the Navy’s need. The California Institute group began the development of such a rocket in late 1943 and early 1944. Tests showed it to be good enough to warrant a special ship to carry and fire it. By early fall 1944, the Navy had completed specifications for such a ship. It w'as found that the LSM could be readily modified to do the job. The super LSM(R)’s already described were the final result.
Just as special ships were required in order to capitalize on the superior characteristics of the spinner, so—it soon became clear—a whole series of spinners would be necessary to capitalize on the superior potentialities of the ships. Accordingly, in the fall of 1944 plans were laid for a family of barrage spinners.
In its essentials, this program called for the concentration of immediate effort on 5-inch spinners with three different ranges: 5,000 yards, 2,500 yards, and 1,250 yards. All were to have the same weight, about 50 pounds, and the same length, about 32 inches. These common characteristics would make for greater ease in handling and stowage, and permit the use of a single type of launcher; yet versatility of use was not to be sacrificed, for a variety of heads would make each of the three models capable of performing a half dozen jobs, from smashing pillboxes to laying down a smoke screen.
Of this projected assortment, a 5-inch spinner with high capacity head and 5,000-yard range was completed first and went into extensive service use. The Institute produced a total of more than 70,000 rounds for the Navy. This saved at least 4 months in getting the spinners into action against the Japanese.

Attack on Iwo Jima

The combat record of the 5-inch spinners justified the time and labor spent in their development. The story has already been told of the four LSM’s equipped for firing spinners which performed notably as part of the rocket fleet during the Okinawa operation. The Okinawa action was the second in which barrage spinners were fired. In the attack on Iwo Jima, in February 1944, the first 5-inch spinners were fired against the enemy from specially equipped LCI’s. Nor did the usefulness of the rocket ships cease with the initial Iwo landing. They lay off shore during the remainder of the operation, delivered harassing fire when targets offered, and call fire as it was requested by the ground forces.
The other spinners beside the model with high capacity head and 5,000-yard range were in varying stages of development when the war ended. The completion of the series is included in the rocket program taken over by the Navy.

7. Bazooka Versus Tank

Among the now-it-can-be-told weapons of the American rocket family, is the super-bazooka, bigger and better version of the footsoldier’s famed tank-buster.
By their surrender, the Germans and Japs missed feeling the impact of a rocket which travels at almost twice the speed and carries double the explosive payload of the standard bazooka projectile; which has an effective range of as much as 700 yards, instead of the 200 to 300 yards of the regular bazooka; and which can function safely through a considerably wider temperature range, thus affording greatly increased protection against the dangers of motor explosion and blast. Though the super-bazooka retains the 2.36-inch diameter of the original bazooka, and is fired from the same launcher, it is propelled by a larger motor, and its heavier explosive charge can penetrate thicker armor plate.
Another development of the original bazooka—still secret at the war’s end—is a super-powered rocket of 3.5 inches in diameter with greatly increased power to penetrate armor plate and reinforced concrete.
The super-bazooka was the joint product of Section H, which produced the design for the motor, and Division 8 of NDRC, which developed the far more powerful head. The 3.5-inch rocket was designed by the Army Ordnance Department.

Bazooka Development
To arm United States infantry to fight tanks on more nearly equal terms, the Army Ordnance Department, in early 1941, had under development a rifle grenade, carrying a “shaped charge” of high explosive. A cone-shaped cup hollowed in the front face of the explosive filling focussed the blast energy into a narrow beam of great penetrating power.
These rifle grenades had too much recoil for field use as a shoulder weapon. Recoilless rocket propulsion was suggested, tried, and adopted. Colonel Skinner, then an Ordnance Department major, and Lt. (now Major) E. G. Uhl, with Section H at Indian Head, undertook the development of a suitable rocket motor.
Following unsuccessful attempts to launch these rocket grenades from attachments to the service rifle, it was concluded that a separate launcher would be required.
To protect the gunner from the rocket blast, the launching tube had to be longer than the maximum burning distance of the rocket motor. To be portable and easily aimed from the shoulder, the launcher, and hence the burning distance, had to be short. By the use of a charge of several thin-web tubular grains of solvent extruded powder in a motor about an inch in diameter, the burning distance was made short enough for a 54-inch launcher, soon dubbed “the bazooka.”
This launcher was designed to be fired from the shoulder and to discharge the rocket blast behind the gunner. It could be sighted and swung with a moving target as easily as a rifle.
The first model of this weapon, despite recognized imperfections,

was rushed through production in 1942. It was used in the first Allied landings in North Africa. The weapon soon became famous for its tank-stopping power in Africa, Europe and the islands of the Pacific.
As is the case with most new weapons, improvements were necessary and development work was continued at high priority. Blast was particularly troublesome, especially at low temperatures which caused the powder to continue burning after the rocket had left the launcher. This was eliminated by using faster-burning powders. One such fastburning powder, developed by NDRC’s Division 8, was a new solvent-extruded powder containing a high percentage of special ingredients—this powder shortened the burning distance so much, even at extremely low temperatures, that it earned the name of “blastless bazooka powder.”

Debut of the Bazooka
This was the weapon whose effectiveness was demonstrated first in the Allied landings in North Africa in 1942, knocking out pillboxes, tanks, and other enemy strong points.
In spite of its short range—it is most effective within 200 yards—the bazooka in the hands of concealed marksmen stopped enemy armor, gave a lift to the morale of the G. I., and was feared by the opposition.
The success of the bazooka in action is best indicated in the unadorned stories of the men who used it. From his European combat experience a private recalled: “We had been hard hit and all of our bazooka men had become casualties.. This Mark VI tank was really giving us a going over, and something had to be done about it. Although I had never used a bazooka before, I knew how to handle it. So one of my buddies loaded the weapon for me and I crawled up a ditch until I was so close to the German tank (he was within 40 yards) I couldn’t miss, and let them have it. That one round really did the trick.” The private won the Bronze Star for his feat.
Similarly, a sergeant, a mortar squad leader, had never fired the weapon, but during a savage German counterattack on American positions he halted a German Tiger with two rounds at a distance of 75 yards.
As the heavy tank lumbered toward him spearheading the Nazi attack, the sergeant seized a bazooka dropped by its wounded operator and fired at the track. The tank’s machine gun as well as supporting German riflemen opened up on him. He reloaded and sent a second rocket crashing home, immobilizing the tank. The crew abandoned it and doughboy riflemen smashed the counterattack. The sergeant won the Silver Star.
Bazookamen found that their improved weapon frequently performed beyond their expectations. Combat reports tell of holes driven through a 6-foot pillbox wall, of masonry walls blasted with holes big enough for a man to crawl through, of tank crews killed by fragments spalled off the inside of 8-inch armor plating although the shaped-charge did not penetrate the armor.

Tank buster—American paratrooper in action in France knocks out a Nazi tank with a direct hit from a bazooka. Note the track being blown off the far side of the tank (SC 1951^').

Bazooka Versus Pillbox
Experience in the Pacific showed that even when the bazooka could not destroy the heavy Japanese pillboxes, its concussion could stun the occupants and give infantrymen an opportunity to rush in and dispatch the enemy at close range. The bazooka was highly effective against Japanese tanks, which were more ’lightly armored than the German.
In one frantic action on Luzon, soldiers of the 6th Infantry Division fought a close-range battle against Jap tanks, which, firing at pointblank range, were mowing down American antitank gunners as fast as they manned their weapons.
“We tore into them with rifle grenades and bazookas, the only weapons we could use under the circumstances,” a sergeant reported. His battalion claimed 57 Jap tanks in the battle.
Combat experience was translated into modifications which made the bazooka a more convenient weapon. A two-piece launcher permitted easier carrying and better concealment from observation than was possible with the original one-piece launcher. A trigger-operated magnetic replaced battery ignition. The sights were improved.
Versatility of the bazooka was increased with the development of a bazooka smoke rocket loaded with white phosphorous; this was effective against Jap bunkers and caves. Ingenious American soldiers projected telephone wire over stretches of exposed ground by fastening the wire to a dummy rocket. They used dummy rockets to carry detonating cables out over mine fields where the cables were set off, exploding the mines.

Nazi Imitations
A new step in the development of shape-charge antitank rockets began with the German capture of American bazookas in North Africa, particularly at Kasserine Pass. The Panzerfaust and the Panzer cKreck were German bazookas based upon the American. Appearing some months after the North Africa action, they carried a heavier shaped charge which produced greater penetration, but were lower-powered and lacked the range of the American 2.36-inch rocket.
The American answer to heavier German /armor and to Germany’s large rockets consisted of the two improved bazooka rockets already mentioned—the super-bazooka and the 3.5-inch rocket.
The superiority of the super-bazooka motor over that of the original bazooka is achieved by the use of an improved ignitor and a heavier charge of propellant, the latter consisting of many thin disk-shaped grains, stacked in a stepped-back column to allow freer flow of the gases toward the nozzle.

8. Rockets for Ground ^^orfore

The explosive powder and the 4,000-yard range of the Army’s folding-fin 4.5-inch aircraft rocket indicated that it could be used as a ground force weapon to supplement the artillery.
As compared with artillery, the rocket lacked range, velocity, and point accuracy, but the absence of recoil made possible the launching of rockets from light-weight devices which were easily moved and quickly set up in places where artillery could not go. Furthermore, by massing a number of launching tubes or rails on a single mount it was possible to fire a great many rockets from one launcher in a very short time.
Saturating the Target Area
When such multiple launchers were used, the inherent dispersion of the rockets became an advantage for certain types of fire; for without changing the position of the launcher the rockets were spread over a beaten zone of predeterminable size. Rockets were able in this way to lay down a drenching fire upon an area target such as a patch of woods, a town, or a supply depot so quickly that energy personnel had no time to take cover. A similar concentration of fire, known as timed fire, could be laid down by artillery, but only after elaborate preparations. Rockets gained the same effect in less time and with the services of only a fraction of the personnel.
“Xylophone” Launchers
The simplicity of launching mechanisms for artillery use of rockets is exemplified by the Army’s “Xylophone,” which consists of eight 7.5-foot tubes mounted side by side and supported by a simple frame which provides elevation from 5° to 45°. The Xylophone weighs approximately 800 pounds and is so compact that two units can be fired from the bed of a 2^-ton truck.
The eight rockets are fired successively at one-half second intervals to prevent the interference which would occur in simultaneous firing. This method, known as ripple fire, is used with all multiple rocket launchers.
Rockets in the Ardennes Bulge
The 18th Field Artillery Battalion in the United States First Army was equipped with 75 launchers. This battalion went on an offensive mission in support of infantry in mid-November 1944. It continued in action until the 17th of December, and on the last 2 days helped materially to resist the German surprise offensive which opened the Battle of the Bulge.
The intensity of drenching rocket fire was demonstrated on one occasion when the battalion fired approximately 1,800 rounds in 18 minutes. Even official reports, usually restrained in their language, called the morale effect on enemy troops “terrific.”
“Calliopes”
Another Ordnance Department multiple launcher, the “Calliope,” was designed to permit a tank to lay down its own artillery barrage. The Calliope consisted of sixty 7.5-foot tubes and was mounted on the

turret of a General Sherman tank. The tubes could be aimed by traversing the tank turret, and elevated by means of the tank gun elevating mechanism. Rockets were ripple-fired at one-half second intervals so that the 60 rockets could be fired in a half minute. After the rockets were fired, the Calliope could be quickly jettisoned from inside the tank if so desired without exposing any of the tank crew. Eleven Sherman tanks of the 710th Tank Battalion, equipped with Calliope launchers, had sufficient firepower to lay 660 rockets on a breakthrough area in a matter of minutes.
Ground Rockets in the Pacific Theater
The rocket’s ability to hurl heavy projectiles from light launchers provided a countermeasure to the Japanese tactic of holing up behind coconut log bunkers deep in the jungles of Pacific Islands. The folding fin 4.5-inch rocket had the power to blast these bunkers, and the Ordnance Department developed an expendable plastic tube launcher in which the rocket was shipped and from which it was fired.
This one-shot launcher as finally developed was 4 feet long, and, complete with the rocket and the tripod on which it was mounted for firing, weighed only 60 pounds. The launcher was designed to fit the standard pack board or could be carried by a shoulder sling and made a load which could be borne through jungle where artillery could not go.
Rocket Situation Well in Hand
The Marines in the Pacific theater used Navy 4.5-inch finned barrage rockets extensively in ground operations.
The Marines’ four Provisional Rocket Detachments each had twelve 1-ton trucks mounting three 12-round automatic launchers, supplemented by lighter installations.
The Rocket Detachments supplied concentration of fire for special needs. When ground advance was held up by a local Japanese strongpoint, the commanding officer would call up as much rocket equipment as seemed necessary. With this equipment came a skeleton crew, which was supplemented for ammunition-parsing and launcher-loading by whoever was available on the spot—riflemen, cooks, signalmen, or machine-gunners. If these localized concentrations of rocket fire did not completely knock out enemy machine gun positions and troop concentrations, they drove the Japanese under cover long enough for other Marines to get to them and overwhelm them.
Ground-fired barrage rockets were used effectively in this fashion on Guam, Saipan, Tinian, Iwo Jima, and Okinawa. One restrained report sums up the verdict on them: “The rockets are very popular with the various combat units because of the effective support they provide.”
A Withheld Threat
Several chemical warfare rockets were developed to meet various anticipated needs. The 7.2-inch chemical rocket had a range of 3,000

“Xylophone” launchers rendered a deadly tune of 1.5-inch rockets in Germany’s Hurtgen Forest. American rocket troops reload while smoke from previous salvos drifts through the trees (S. C.207018).

yards and carried a payload of 20 pounds of gas or other chemical agent.
Had the enemy resorted to gas, rockets as a means of laying down gas would have fulfilled a requirement imposed on the Allied Forces by the sort of war they were fighting. Our forces were going forward in an offensive war. That made presistent gases undesirable to use because we expected soon to occupy the territory upon which the gas had been dispersed. Thus it was necessary to specialize in the use of nonpersistent gases. But these are effective only if high concentrations can be laid down in as short a time as 90 seconds. The characteristics of rockets made them a natural weapon for this use.
A modification of this 7.2-inch chemical warfare rocket was designed for the laying down of smoke screens.
To make possible the rapid firing of intense barrages of 7.2-inch chemical rockets, the Army’s Grand Slam launcher was designed. It could be mounted on a 2%-ton truck or on the ground and it fired a barrage of 24 rockets at one loading.

Demolition Rockets
To shatter heavy reinforced-concrete beach barricades or other strongly fortified positions, the 7.2-inch demolition rocket was developed. It was a close-range weapon quickly adapted from the mousetrap antisubmarine rocket. Its thin-walled head carried 32 pounds of plastic explosive which on impact spread over a large area of the target on detonating, had a tremendous destructive effect. Because of the rocket’s short range it was generally fired from an armored launcher impervious to small arms and machine gun fire.
The launcher, known as the Whiz Bang, was mounted on a General Sherman tank. Whiz Bangs and 7.2-inch demolition rockets were included in the invasion army which landed in southern France in July 1944.
The Navy also used the 7.2-inch demolition rocket and for its firing from LCM’s developed a 120-barrel launcher nicknamed the Woof us. Many rounds of this rocket were fired by the Navy at Salerno, the Anzio beachhead, and during the invasion of southern France.

Target Rocket and Harpoon
A number of other uses were found for rockets in ground warfare. In August 1941, the Coast Artillery, which was responsible for training antiaircraft crews, asked the Army Ordnance Department to develop a target rocket to supplant the slow, towed sleeve-targets then in use.
Section H and the Ordnance Department worked together to modify an experimental 3.25-inch rocket motor and mounted large, target-size, plywood fins on the rocket. As standardized this target rocket had a range of approximately 1 mile and a speed of about 360 miles an hour. Occasional erratic flights which would have been undesirable in a high-explosive rocket simply increased the realism of the target for antiaircraft training. Sometime later the CIT

Sherman tanks with ⁱ;Calliope” launchers ready, to loose a salvo of 2Ji0 4.5-inch rockets on enemy positions await the signal to go into action near Beisdorf, Germany (ETOHQ .

laboratories developed new types of target rockets with velocities up to 425 miles per hour.
A rocket solution for the age-old military problem of getting a line across a river or other difficult obstacle was arrived at in the double-motor harpoon rocket.
The harpoon rocket consisted of two 4.5-inch rocket motors connected in tandem and fitted with a pointed head equipped with four folding spades. A wire cable was attached to the rear nozzle plate. On firing, the rear motor was ignited and drove the rocket upward trailing the wire cable behind it. After the rocket had passed the peak of its trajectory, a delay fuze ignited the forward motor which accelerated the rocket and drove the spade head deep into the earth. A pull on the wire rope opened the spades and provided a solid anchorage.

Army Spinners
The advantages of spin-stabilized rockets over finned types for amphibious warfare—ease of handling and better accuracy from shorter launchers—were equally valuable in land warfare. In late 1943 the Army Ordnance Department initiated development of its 4.5-inch spinner. In comparison to the 4.5-inch folding fin rocket, the spinner, though it retained about the same total weight, carried a heavier payload with better accuracy to a greater distance—5,250 yards instead of 4,000. This increased range allowed more flexibility in the choice of firing positions; in particular it made it possible to fire from positions beyond the range of most enemy mortars.
Large-scale production of this rocket, standardized as the M-16, was undertaken by leading industrial concerns to meet Army Ground Force requirements. Development of VT fuzes for these rockets, to give them the advantages of air burst, was completed, but the war ended before they could be used in combat.

Honeycomb and Hornet’s Nest
Two multiple launchers comparable to the Xylophone and Calliope were developed by Army Ordnance for the 4.5-inch spinner rocket. The Honeycomb, which replaced the Xylophone, was a 24-tube, 1,200 pound multiple launcher mounted on a two-wheeled carriage. The Hornet’s Nest, which replaced the Calliope on General Sherman tanks, was a cluster of sixty 36-inch tubes.
The spinner and its launchers were late developments in the war, and the first Honeycomb launchers and spinner rockets sent as a special mission to ETO pursued the retreating Germans across central Germany and into Czechoslovakia before they found a suitable target in the remnants of a Panzer division dug in at the edge of a woods. From a range of 4,670 yards three Honeycombs threw 71 rounds in 15 seconds against the enemy with “good effect.”

Rocket Field Artillery
At about this time five rocket battalions were being organized and trained by the Field Artillery at Fort Sill, Okla. Each was equipped with 36 Honeycomb launchers for firing Army 4.5-inch spinners. One of these battalions was on Okinawa and another in the Philippines, in preparation for the assault on the Japanese home islands, when the war ended.

9. Specialized Uses of Rockets

Rockets were called on to perform numerous miscellaneous tasks, the variety of which were proof of their versatility. Since rocket motors are pure reaction propulsive systems, they were used to push things which were not missiles.

J ATO
A most important illustration of this type of application is the development and service use of JATO (Jet Assisted Take-Off) for airplanes. Safe, dependable JATO units were used during the war in combat operations by Naval Aircraft, and are still in operational use by both Naval Aviation and the Coast Guard.
Both the AAF and the Navy were working on JATO sometime before December 7, 1941.
The Army Air Forces initiated their JATO work in 1939 when it contracted with the Guggenheim Aeronautical Laboratory of the California Institute of Technology for the development of JATO equipment. In August 1941 a small AAF Ercoupe Airplane fitted with several small GALCIT JATO units made the first successful jet-assisted take-off in the United States.
The GALCIT propulsion unit was powered with a newly developed solid fuel which could be easily manufactured and loaded in the JATO unit. Following the promising initial tests the work was continued at high priority to meet rigorous requirements for safety and reliability in service use. The initial technical problems were solved and the AAF contracted with the Aerojet Engineering Corp, for further engineering development and production.
The GALCIT group and later the Aerojet organization undertook the development of JATO units powered with liquid fuels to meet thrust requirements for longer time intervals not readily obtainable with solid fuels. Both liquid and solid JATO units were tested by the AAF on most of its standard aircraft, including P-38, P-40, P-59, AX20, B-17, B-24, and B-29.
Early in 1941, the Navy’s Bureau of Aeronautics established a rocket research group at Annapolis, Md., where intensive work primarily on long burning liquid-propellant units was undertaken. As a result this group on September 23,1942, made the Navy’s first JATO take-off using a liquid-fueled rocket designed by the late Dr. Robert H. Goddard.
The Navy was interested in JATO for two purposes: First, to shorten the take-off runs of carrier-based planes, and second, to enable large flying boats to take off in restricted areas, in rough waters, or in an overload condition.
In order to proceed rapidly with both liquid and solid propellant rocket developments, the Bureau of Aeronautics set up a program including, in addition to the Annapolis group, the research organizations of the Aerojet Engineering Corp., Pasadena, Calif, and Reaction Motors, Inc., Pompton Plains, N. J.
Solid or liquid JATO units developed by these three agencies were successfully installed and tested in most of the Navy’s airplanes in-

eluding PBY, PB4Y, SBD, PBM, SB2C, TBF, F4U, F4F, F6F, PV, PBJ, 0S2U, J2F, and SC, with excellent results.
After considerable experimentation with long-duration units using both liquid and solid propellants, the Bureau of Aeronautics decided that most operational needs could be met by the Aerojet 12 second solid fuel units, provided they were fired at the proper point on the take-off run. These 12-second JATO units could be shipped, handled, and installed in the field more readily than any other type. Therefore the Bureau of Aeronautics embarked on a large-scale production program and thousands of such units were procured and used.
Seeking further improvements, the Bureau of Aeronautics requested Section H to develop a new propellant charge for the JATO unit to give more reliable performance at low winter temperatures and less smoke than the standard units. This project was started in December 1944 and in less than 6 months a new unit of reduced duration but otherwise satisfactory, was successfully developed and tested. Plans for limited production of this unit were dropped when Japan surrendered in August 1945.
The extensive use of JATO equipment has resulted in hundreds of routine take-offs under otherwise adverse conditions. JATO has been used several times most effectively for salvaging aircraft forced down in areas where normal take-off would be impossible. And, most distinguished service of all has been the spectacular record of JATO in air-sea rescue work.

Rockets Launch Buzz Bombs
A program of fundamental research which paid dividends by the end of the war was that leading to the production of molded composite propellants, an enterprise conducted by Divsion 8 NDRC, together with the Monsanto Chemical Co. The propellants are made by molding under high pressure, a mixture of ammonium picrate, sodium nitrate, and a plastic to produce giant propellant grains, weighing upwards of 120 pounds each. Rockets charged with these grains burn for about 2 seconds, and give an extremely high thrust. A few of these rockets attached to the launching carriage of the American version of the German V-l bomb send it safely and surely on its course for a simple, short launcher. In this application, the rockets eliminate the large, fixed, launching installation which the Germans employed.

Rocket-Propelled Window
In the fall of 1943, the Navy’s Bureau of Ships and the Bureau of Ordnance went to work on the development of another new rocket— this time as a means of projecting “window” from surface vessels, “window” being a pack of metalized paper strips which, when released in midair in the path of a radar beam, acts as a temporarily effective countermeasure against enemy radar observations.
As ultimately developed, window rockets are modified 3.5-inch aircraft rockets launched from ships. At approximately the peak of the trajectory the head ejects a load of strips three-sixtenths of an inch

J ATO: The take-off run of a Martin Mariner is reduced approximately 30 percent Try the use of four “Jet-Assisted Take-Off'¹'’ units—an application of rocket power (BuA 189950).

wide and of various lengths from 1% to 16 inches, to reflect radar beams of many wavelengths. One head may contain as many as 76,800 strips. When window is ejected, the enemy sees an extra spot on his radar screen which stays there after the true target moves away;
The first operational use of window rockets was during the Normandy invasion. They were issued for use against fire-control radars not already knocked out by bombardment. In southern France, PT’s and converted aircraft crash boats used window rockets successfully against German radar. The PT’s were screening a task force on D-day plus two, and enemy searchlight and gun radars were effectively deceived. The PT’s fired their window rockets and shortly thereafter, the searchlights moved to the window cloud and the gunfire shifted. The Germans thought an air attack was under way.
A minesweeper skipper operating in Cherbourg harbor in broad daylight was under attack by coastal batteries. He fired about 20 window rockets and soon saw the pattern of fire move away from his ship and become confused. A few minutes later, the window had fallen, and he again became the target. After firing more window rockets, he was able to take his ship from danger.

Smoke Rockets
Smoke rockets, fired from ships and planes, were used successfully in amphibious operations from New Guinea to Okinawa to lay screens ahead of landing craft, mark targets and range salvos of high explo-0 7 O O OX
sive rockets.
The Navy Bureau of Ordnance realized the need for a smoke rocket early in 1943. The 4.5-inch high explosive barrage rocket was adapted to carry a smoke charge and burst on impact. CIT was asked to make the modification and shipped the heads less than 2 weeks after receiving the request. This rocket had a maximum range of 1,100 yards and several thousand were loaded during the summer of 1943.
In May 1943, CIT began work on a head which included a tetryl burster for greater dispersion of the smoke. This new head proved superior for laying screens over both land and water.
In June 1943, a 3.5-inch high velocity smoke rocket to be fired by aircraft was called for. The work was done by CIT and by August 1943 a suitable smoke head for the 3.5-inch aircraft rocket had been developed and tested.
The first rockets for both ships and planes were loaded with FS liquid smoke, a mixture of sulphurtrioxide and chlorosulphonic acid.
Experiments with a white phosphorus filling showed that it was only slightly less effective than the FS loading for screens, that it had antipersonnel and incendiary value, and that it was longer burning at the source.
During the latter part of 1943 and early in 1944 a means was developed for plasticizing white phosphorous which gave it considerably higher screening and antipersonnel effect. Filling of 4.5-inch rockets with the plasticized white phosphorus began in March 1945, with the Amphibious Forces requiring 10,000 per month.

Rocket Push and Pull
Many applications of rocket motors were made in which the motor merely supplied a push. One device is the “Donnerkeil”—a German

development which enables the engineers to dig holes for telephone poles with a minimum of time and effort. The Corps of Engineers, the Ordnance Department, and Section H cooperated to develop an improved “Donnerkeil.” It consists of a steel rod nearly 6 feet long, with a propellant chamber at one end. The force supplied by the propellant when it is fired drives the rod approximately 6 feet into the ground. The hole left when the rod is pulled out is slightly more than an inch in diameter and is easily expanded by an explosive charge so that it will accommodate the telephone pole.
Rocket motors developed at the Allegany Ballistics Laboratory of Section H were also used to lay devices to detonate enemy mine fields. The “Snake” was built in the form of an elongated ski about 100 feet long, made up of two layers of overlapping metal plates, each 5 feet long and 5 inches wide. Cartridges of TNT were clamped between the layers. The head of the snake carried a rocket motor, and the tail a trip mechanism. The ski shape allowed the snake to travel over obstacles. In operation, the Snake was dragged to the border of the mine field. Then the rocket motor would be fired, pulling the Snake into the field. At this point the trip mechanism would detonate the charge and the explosion would set off the mines.
Other devices to clear mine fields were also developed during the latter part of 1944 and the early months of 1945. One of these was the “Detonating Cable Kit.” This included a cable containing high explosive, and a rocket motor developed by the Section H workers. In use, the cable was projected by the aid of the rocket motor so that it lay across the mine field. Then the explosive cable was set off, clearing a path through the mines. A U-shaped rocket motor was developed for this kit, consisting of two motor chambers connected at the front end, each chamber having its own nozzle at the rear.

Recoilless Guns
In the latter months of the far, the Army had three recoilless guns in the field—a 57-mm. shoulder rifle, a 75-mm. rifle mounted on a machine gun tripod and a 4.2-inch mortar similarly mounted. These useful weapons combine the accuracy of a rifled gun with the absence of recoil, lightness, and mobility of rockets. They are truly “stationary rockets,” capable of being fired repeatedly like other artillery weapons. The first two of these weapons were developed by the Ordnance Department, the third by the Chemical Warfare Service and Section H at the Allegany Ballistics Laboratory.
The detailed story of their development cannot be given here; some information on these weapons has been released previously.

OSRD Demobilies
Immediately following the surrender of Japan the research laboratories of the Office of Scientific Research and Development received their demobilization orders. The job of providing new weapons for the fighting forces during the period of national emergency was finished and the immense task of reconversion required the return of scientists and engineers from war work.
OSRD's termination plans provided, however, for transferring selected projects, facilities, equipment, and “know how” to permanent Army and Navy establishments in order that the “values” of 5 years

of intensive scientific work might be preserved. ORSD scientists were asked to prepare comprehensive technical reports covering all phases of wartime research and development for the use of those who were charged with continuing the work. Of equal importance to the Services were the civilian rocket experts who accepted permanent employment in Service establishments. These rocket scientists constitute a valuable nucleus for carrying the peacetime development programs of the Army and Navy.

Importance of Fundamental Research
During the war years, rocket development workers were forced to seek quick and expedient solutions using materials, processes, and designs available with minimum delay. Nevertheless, many promising lines of fundamental research were uncovered which could not be investigated thoroughly for lack of time and scientific manpower.
It is to be hoped that these promising avenues of investigation will be explored during the years ahead when the demand for immediate answers will not be so urgent. The development of improved rocket ordnance for the armed forces of the Nation will require a comprehensive basic research program.
The fundamental scientific work which underlies the development of new weapons is illustrated in the work on spinner rockets for firing from high-speed aircraft. Real progress in design required better understanding of the behavior of the spinning projectile from the moment of launching from the aircraft throughout its flight. An ingenious instrument, called the “solar yaw camera,” was devised by CIT ballisticians to provide accurate data on the motion of the spinning rocket along its trajectory. This device is essentially a small, rugged, pin-hole camera which can be mounted in the head of the rocket. As the projectile rotates and yaws in flight, sunlight enters through the pinhole for an instant during each revolution and produces a spot on the camera film. The resulting film gives a record of the orientation of the projectile in space at many points along its trajectory. From such data the physicist and mathematician can work out the nature, magnitude, and direction of the forces acting on the rocket during its flight. Carefully planned experiments can then be arranged using modified rocket designs with different shapes, weight distributions, velocities, accelerations, rotational speeds, launching conditions, etc.
Such experiments provide basic knowledge concerning the behavior of spinning rockets and the effects of the above design factors on performance and accuracy. Without such data the rocket designer is almost helpless and is forced to proceed using slow, wasteful, “trial and error” methods.
This is but a single example of how basic research underlies the design of a weapon. Ordnance engineers can improve our weapons more rapidly as the basic scientific knowledge on which they build is broadened and deepened along every line.

The Services Carry On
Qne of the new, permanent service laboratries is BuOrd’s Naval Ordnance Test Station (NOTS), located in the Mojave desert near

Inyokern, Calif. Its construction was started in 1943 to provide an experimental center for the development of aircraft ordnance, including rockets. In 1944 NOTS assumed the job of field testing new Navy rockets and the early training work with Navy pilots. By 1945 the station was equipped and staffed to take over certain phases of the development program, and the transfer of projects, personnel, and equipment from the CIT rocket laboratory was begun. Following VJ-day the process of transfer was accelerated and completed in December 1945.
The facilities of the Allegany Ballistics Laboratory of Section H have also been turned over to the Navy. The Hercules Powder Co. will operate the laboratory under a Navy contract. A joint Army-Navy research program is planned to continue the development of improved types of rocket propellants and their application to “thrust units” for a variety of military purposes.
Both the Army Air Forces and the Army Ordnance Department have arranged for rocket work to be carried on in their research establishments and arsenals, as well as by contract with some of the leading industrial and academic institutions of the country. Among the facilities being continued in operation to meet needs of both of these services are the supersonic wind tunnel at Aberdeen and the pilot plant at Dayton for composite rocket propellants.

Weapons of the Future
The weapons described in this report were developed to meet operational needs arising from tactical and stratgic situations in a modern yet largely conventional type of warfare. That our traditional concepts and methods of warfare will become outmoded by the advent of more efficient and powerful methods of destruction is almost certain. Nevertheless, until new weapons appear, vastly superior to those we now have, there is good reason to continue the development of today’s weapons.

U. S. GOVERNMENT PRINTING OFFICE: 1946