The M129 is a 40 mm automatic grenade launcher that was used as an aircraft weapon in United States service.

The M129 was used with the chin-mounted M28 series armament subsystem used on the AH-1G, AH-1Q, MOD AH-1S, and production AH-1S Cobra.

The M129 was also used on the: The M129 was effectively a redesign of the older M75 to incorporate a concentric cam and improved mount.

[3] The major problem with the M75 was the torque created due to the barrel being below the operating drum.

Some other improvements were made to the M129, most notably that of the addition of special feed tray to permit the firing of low-velocity and high-velocity ammunition, a mechanism to provide instant interchange between electric operation and manual hand-crank operation and a dynamic braking unit to guarantee that the launcher barrel always stopped in the forward (safe) position when the firing trigger is released.