Rocket Test Program, Hangar 1301

Building 1301 is the home of the Air Mobility Command Museum. From 1944 to 1946 it housed the headquarters and engineering facility for the 4146th Army Air Force Base Unit. It was that unit that developed the first successful combat proven air-launched rocket systems used by the United States Armed Forces.

History does not record the individual who first conceived of the idea of using an aircraft as a rocket launcher; however, experiments were being conducted in the United States during the early part of World War II with that concept in mind. Initial American efforts at developing air-launched rockets and missiles were located at a number of civilian and military installations across the country. The principal testing facility was the Aberdeen Proving Ground in Maryland with some of the coordination for the development being done at Wright Field in Ohio.

The first efforts to place rockets on aircraft were tried by the Army Ordnance Department. They used an experimental 4.5” rocket that was attached onto the wing of a P-40 aircraft at Wright Field. This aircraft was flown to Aberdeen for test firing. The blast encountered, upon the launch of the rocket, was greater than anticipated and modifications to the rocket and the launcher were required. The first successful ground firing of these rockets, from an airplane mount, was on July 6, 1942 and aerial firing test were conducted in the fall of 1942.

Testing of these rockets and launchers continued at Aberdeen during 1943. The original steel tube launchers were replaced with plastic tubes in the spring of that year. Other improvements were made before quantity production was begun in May. Early production models were not always reliable. One of the main problems was the premature separation of the rocket’s warhead from its body. These problems remained with the rockets for some time after they were issued to combat units.

The preliminary results of the testing and development program demonstrated that the air-launched rocket could be an effective weapon against ground targets, especially those that were difficult for conventional bombers to reach. The ability of the rocket equipped fighter to move low over a target and release a rocket more directly at the target meant that a fighter aircraft could be a more versatile weapon during the earlier period of the war.

A series of meetings were held during the late fall of 1943 on the necessity to advance the Air Force’s involvement in rocket development. By early 1944, the Army Air Force was ready to create a special unit for the continued development of air-launched rockets. The Ordnance Department asked the Army Air Force’s Commanding General to create the unit at Dover Army Air Field. On April 1, 1944, the Army Air Force ordered the establishment of an accelerated rocket development program with the creation of a base unit and experimental rocket station at Dover. The unit was formerly activated on April 24, 1944 as the 732nd Army Air Force Base Unit under the jurisdiction of the Army Material Command. The unit designation was changed to the 4146th on August 31, 1944. The unit was to develop, fabricate, install and test all likely means of launching rocket propelled projectiles from aircraft.

Among the items that the 4146th was to study was the 4.5” launcher already in production. In addition, they were to study the possibility of manufacturing launchers for rockets up to 16” in diameter. The unit was also directed to develop launchers for bombers, multiple launching tubes and tubes having a flexible installation for firing both forward and rearward. The unit would also examine and test foreign rocket devices including those developed by the British, Russian, German and Japanese Air Forces. Additional missions included testing vertical bombs and German rocket propelled bombs.

The first rockets to be used in combat were shipped to the China Theater of Operation in October 1943. This shipment was made at the same time the Army Air Force was preparing to establish the testing station at Dover Army Air Field. The first shipment consisted of 2,900 rounds of rockets and launchers for a squadron of P-40s.

After several months of pilot and ground crew training, the first rocket combat mission was against an airfield on Hainan Island on March 4, 1944. The attack was carried out by the 74th Fighter Squadron, 23rd Fighter Group of the 14th Air Force. The flight consisted of eight planes. Only four of the planes were able to effectively fire their rockets. The other planes either suffered mechanical failure or experienced pilot error during the raid. The four successful planes fired six rockets each and caused considerable damage to the airfield and to the vehicles and aircraft on the ground.

The facilities constructed for the 4146th Base Unit at Dover consisted of an experimental station with a hangar, power plant, shop area, an administrative building, barracks, a mess hall, hardstand, an ammunition storage area and a firing range. The firing range¹ was located near the Delaware River about ten miles from the base. Building 1301 was the hangar, power plant and shop area combination as it was designed as one large building.

The rocket development program at Dover progressed rapidly. In July 1944, a civilian engineer from Dover was sent to Burma to supervise the installation of the rocket launchers on the fighter planes. He also provided training in the use of the rockets to the pilots and ground crews. While there, he assisted in the field modification of the mounts on the P-51 so that aircraft could carry both bombs and rocket launchers.

The second part of the engineer’s mission to Burma was to supervise the installation and use of a rapidfire rocket launcher on a B-25. This launcher was designed to be mounted within the fuselage or wing structure of the airplane. The launcher was designed by the staff of the 4146th and manufactured by the United Shoe Machinery Corporation. The design proved unstable due to the number of moving parts that came in contact with the exhaust blast of the rockets and the poor quality plastic launching tubes. The staff of the 4146th reworked the initial design based on the combat tests in Burma. These were later incorporated into a successful design.

As the rocket program progressed at Dover, it became obvious that additional testing facilities were needed and that closer communication was required with the manufacturers. Accordingly, in September 1944, an experimental rocket range was established at the Material Command Fighter Test Base at Muroc, California². This range and its personnel were under the command of the 4146th Army Air Force Base Unit.

Soon, scientists at the California Institute of Technology produced a successful 5.0” rocket. This rocket had a speed and a weight range that was able to meet the Air Force’s needs for the remainder of World War II. It was thought that this rocket could also be used against the launch points of the V-class rockets that Germany was using against Great Britain. These launch points were called CROSSBOW sites.

On June 28, 1944, the 4146th installed the 5.0” rockets on the aircraft that were sent to Great Britain. However, intelligence reports showed that the German rockets were being launched from mobile ramps instead of the original concrete bunkers. These ramps were difficult to locate and when found could be destroyed by conventional bombs.

The mission of the Dover team was then changed. They would equip a squadron of P-47 Thunderbolts with the new rocket, train its flight crews in its use and help to use the rocket against battlefield targets. These targets would tend to be tanks and gun emplacements that were difficult for the bombers to destroy.

The 513th Squadron, 408th Group, 9th Air Force was the unit chosen for this task. During July 1944, this squadron flew three missions with rockets. The first mission destroyed a large concentration of locomotives.

The second was against an airdrome south of Paris. This raid resulted in the destruction of five airplanes and numerous hangars as well as German staff cars. The third raid was against a freight train, destroying three locomotives. In addition, several tanks were destroyed on the train’s flatcars.

The pilots involved in these actions were very impressed with the ability of the rockets to destroy large targets. They did, however, make a number of recommendations for modifying the launchers and to the tactics that were needed to effectively use the new weapons. These suggestions were taken back to Dover and to the field testing facilities at Muroc. The suggested modifications were made to the rockets and these improved versions saw extensive combat during the final months of the war in Europe.

The work on air-launched rockets conducted by the 4146th Base Unit was the beginning of a new type of air combat experience for the American pilots around the world. The rocket, while it did not end World War II, was part of a technological shift in combat that would be felt during the combat actions of the Cold War era. Inexpensive and efficient rockets made it easier for smaller combat aircraft, such as the jets of the Korean War, to move against ground targets that would not have been accessible to traditional bombers. Also, the use of air-launched rockets in aerial combat meant that aircraft could stand off from each other during engagement and fire at each other using electronic means to lock onto the target instead of up close visual sightings.

¹ The range was located in what is now the Bombay Hook National Wildlife Area, approximately ten miles northeast of Dover Air Force Base.

² Muroc Field was renamed Edwards Air Force Base after Glen W. Edwards who was killed there flight testing a YB-49 “Flying Wing.”

Building 1301 was placed on the National Register of Historic Places on December 7, 1994.

Sources: U.S. Department of the Interior, National Park Service; National Register of Historic Places NPS Form 10-900a (8-86), dtd. 5 July 1994