The Corporal M2: America's First Nuclear Guided Missile
The last six Corporal E rounds were flown during the period between July 11, 1950, and October 10, 1951. A lightweight, transistorized guidance unit was installed in round 7. Recognizing the rapid pace of electronic advances, the interchangeability of guidance units was one of Corporal’s initial design criteria. Round 11 provided the basic pattern for the future weapon with its characteristic delta fins and a payload section reconfigured to house a W7 tactical warhead. This increased the missile’s length to 45 feet, 4 inches. Authority over the missile was assigned to the Ordnance Guided Missile Center (later the Army Ballistic Missile Agency) at Redstone Arsenal near Huntsville, Alabama, following its formation in April 1950. The first 27 operational Type I tactical rounds were manufactured by Douglas. But on December 10, 1951, a production contract for 200 missiles was signed with the Firestone Rubber Company at a staggering price of $13,695,000. Testing of the Firestone missiles began on August 7, 1952.
Sixty-four Type I missiles were launched in contractor evaluation and engineering test programs prior to deployment. The operational philosophy for Corporal was a vertical launch followed by a tilt of several degrees to one of a series of preprogrammed “zero-lift” or non-maneuvering trajectories after four seconds. Fuel shutoff at the proper moment was used to achieve the desired range. It was quickly realized that to establish accuracy, a new high-speed fuel shut-off was required. This new piece of hardware would undergo a continuous series of improvements. Type I Corporal missiles could engage targets at ranges between 30 and 75 miles, with a trajectory that reached a maximum altitude of 135,000 feet. The final speed of the missile as it descended on the target was between 1,500 and 2,500 feet per second, depending on the range.
Accuracy was further improved in the Type I missile by means a terminal correction provided by its new guidance unit. Unlike modern missiles in which the warhead and missile body separate, in Corporal the pieces remained joined until impact, contributing to trajectory variance. A pair of accelerometers added to the existing gyros provided fine control for the arrangement during descent. Exterior control used a modified SC-584 fire-control radar designated AN/MPQ-25. It provided trajectory information while two Doppler antennae measured velocity. Between 95 and 130 seconds into flight, a computer-calculated correction, based on telemetry and radar guidance, was sent to the missile to be implemented at impact minus 20 seconds. The maximum adjustment possible was 1,200 meters. Based on the likelihood of striking a target, the Doppler system sent an arming command to the warhead. Nevertheless, only a meager 27.1 percent of test rounds fell inside of a 300-meter radius. Mechanical and electronic reliability was a disappointing 47.1 percent.
The story of the development of Corporal’s semimobile handling, launching, and servicing equipment was largely one of having to educate manufacturers in a new phase of the armament industry. Initially, a Corporal battalion consisted of two batteries or launchers, 250 men, and 35 vehicles. These vehicles and Corporal’s shipping containers were designed by a combination of private industry and JPL, but ultimately they were produced by Firestone. They included a mobile erector launcher, missile-warhead transportation, propellant, service, compressor, guidance and computer vehicles, plus an electronic shop. The first tactical launch using this equipment occurred on July 7, 1953.
Launching Corporal was a complex process that took eight to nine hours. After getting within range of a target, the guidance site was selected. Then, in order for the missile to bear on the target, the portable launchpad was located at a firing site no more than 600 meters distant from the target line and no more than minus-200 to 2,800 meters from ground radar. After this was accomplished, the 4,400-pound missile body was removed from its storage container at a service site and placed on a test bed for assembly and installation of its fins. At this time, the firing station was set up. Following attachment of the missile body to a horizontal rail, the extremely hazardous fueling procedure was carried out by a crew wearing bulky protective clothing. After fueling, the systems were checked and “peaked,” and the W7 atomic warhead was mated to the body. The erector-launcher then transported the 11,400-pound, operationally ready missile to the launch site. The missile was lowered vertically onto its launchpad and a registration mark on its body was placed into correct alignment with the target in order for it to guide accurately. Following the attachment of all necessary umbilicals, pressurization, and a final check, the erector and servicing vehicles were withdrawn and the missile was launched.
Training and educational material were considered just as important as the development of the missile and its tactical equipment. Operating a sophisticated missile armed with an atomic warhead was far more complex than slapping a shell into a breech and yanking on a lanyard. The first JPL training school began operation in July 1951, with five ordnance and five field forces personnel. Graduates from the first two classes were assigned as instructors at guided-missile schools established at Redstone Arsenal and Fort Bliss, Texas. A printed maintenance plan for the guided missiles and their ancillary equipment followed. By March 1952, three Corporal field artillery battalions had been activated and a direct support company formed.