M129 40mm Grenade Launcher

The M129 grenade launcher is a 40x53mm, cam-operated, electric motor driven, air-cooled, grenade launcher that has a rate of fire of 440 rounds per minute. The weapon's drum cam feeds linked ammunition into the weapon and also controls the rate of fire. The weapon's barrel cycles back and forth as part of the firing process, with the rear battery position effectively locking the cartridge in during the fire phase of the operation cycle.

The M129 launcher was derived from the M75 grenade launcher, with the most obvious difference being the replacement of the M75's off-set drum cam with one concentric to the bore. The development of the XM129 started in 1963 at Philco-Ford in order to address various issues with the design of the M75. Among other improvements, the weapon is stopped only after a full revolution of the cam, with the barrel forward and no live round potentially chambered.

Subsequently type classified as the M129, over 1,667 units were built by Philco-Ford before 1971 and by the Maremont Corporation from 1972 onward. The weapon served as the replacement for the M75 in the development of the M8 armament subsystem that had begun during the Light Observation Helicopter competition. It was an optional weapon for use in Emerson's Tactical Armament Turret 141 (TAT-141), adopted by the US Army as the M28 series of armament subsystems, and utilized on the AH-1G, AH-1Q, and variants of the AH-1S helicopters. The weapon was also part of the development of the AH-56A helicopter, being used in Emerson's TAT-124, which was assigned the designation XM51. The XM94 armament subsystem for the UH-1 series of helicopters, allowed an M129 to mounted at one of the doors.

The M5 armament subsystem was also modified between 1967 and 1968 to accomodate the M129, but it is unclear how many systems were refitted. During 1966 and 1967, Philco-Ford had also explored utilizing the M129 as a ground weapon (as they had done with the M75). Modifying the weapon with the manual crank in lieu of the power drive system led to the XM173, which was not adopted. A modified version with spade grips for mounting on vehicles was also developed in 1968, designated as the XM182. This weapon was also not adopted.