Armored personnel carrier, 37mm gun mount
In 1952, the U.S. Army outlined a three phase program to develop improved light antiaircraft weapons capable of dealing with high speed jet aircraft. The first phase of the program involved the upgrade of the existing twin 40mm self-propelled gun T141 (later the M42) by the addition of a range only radar. This project, nicknamed Raduster, was unsuccessful and it was finally canceled.
The second phase of the program resulted in the development of a 37mm gun, six barrel, Gatling type gun named the Vigilante. This weapon was proposed in two versions, the towed Vigilante A and the self-propelled Vigilante B. The final phase of the search for a new antiaircraft weapon was devoted to a new self-propelled guided missile system named Mauler.
Initially, it was intended to produce four pilots of both the Vigilante A and the Vigilante B. However, the number of pilots was subsequently reduced to three in each case.
Designated as the 37mm antiaircraft, full tracked, self-propelled gun T249, the Vigilante В utilized a low silhouette armored chassis based upon the M113 armored personnel carrier. Mounted in an armored turret, the weapon itself consisted of the 37mm gun mount T250, the 37mm gun mount T194, the fire control system T51 including the XM17 radar target alarm group, and the XM8 constant speed control generator-transmission.
The aluminum alloy armor on the T249 was equivalent to that on the M113 armored personnel carrier. Although using the same power train components as the M113, the chassis was lengthened increasing the ground contact length to 110 3/4inches and the height without the turret could be reduced to 52 inches. The suspension incorporated a lock-up system to stabilize the vehicle when firing.
The turret mounted 37mm gun T250 had a muzzle velocity of 3,000 feet per second and a firing rate of 3,000 rounds per minute. For ground targets, the latter was reduced to 120 rounds per minute. The magazine on the weapon had a maximum capacity of 192 rounds and it was reloaded manually.
By 1960, the pilots had been completed and were being evaluated. However, other automatic weapon systems were now under consideration and the Vigilante never reached production.
A triple mount of the Hispano-Suiza HS820 20mm gun was proposed for installation on the M113 armored personnel carrier and the M548 cargo carrier. Each of the three weapons had a firing rate of 1,000 rounds per minute providing a total rate for the triple mount of 3,000 rounds per minute. Adaptation of the Air Force Vulcan 20mm Gatling type gun to a ground mount also was in progress at Rock Island Arsenal beginning in 1964. The ground version of this weapon was electrically driven with a maximum firing rate of 3,000 rounds per minute.
Installed on a modified M113A1 chassis, the new weapon was designated as the 20mm self-propelled antiaircraft artillery gun XM163. It consisted of the 20mm gun XM168, the gun mount XM157, the radar set AN/VPS-2, and the automatic lead computing sight XM61. It also was referred to as the Vulcan Air Defense System (VADS).
Standardized as the Ml63, and after some modification of the gun mount as the M163A1, the VADS began production at the General Electric Company in 1967. The modified M113A1 armored vehicle used to carry the weapon system was designated as the M741. It utilized the same power train and suspension system as the M113A1 except that it was equipped with a lock-up device to stabilize the vehicle when firing.
The weight of the weapon greatly reduced the freeboard of the vehicle when afloat. To retain its swimming capability, flotation cells were installed on each side of the M741 and a high displacement trim vane was fitted. When the improved engine cooling system was introduced on the M113A2 armored personnel carrier, a similar installation was made on the M741 and it was designated as the M741A1. The later suspension with the increased wheel travel was not applied to the vehicle since it was incompatible with the lock-up system required for the weapon.