The M197 utilized by the AH-1 aircraft is a lightweight short-barreled three-barrel Gatling type gun. The M197 20mm Automatic Gun utilizes a rotary action mechanism, contained within a fixed rotor housing, and a rotating barrel cluster. The M197 utilizes a rotary action mechanism, contained within a fixed rotor housing, and a rotating barrel cluster. Drive power is provided by an electrically driven gun drive mechanism. In practice the M197 automatic gun has a firing rate of 730 ± 50 spm (shots-per-minute), though in principle the M197 has a selectable firing rate of 2000-3000 spm.
The M-197 in the AH-1 is mated to an ammunition storage and handling system that has a capacity of 700 rounds of linked M-50 or PGU series electrically primed ammunition. The M-197 utilizes the M-89 or M-89E1 declutching feeder to delink and feed ammunition into the gun. The M-197 is attached to the A/A49E-7 turret assembly that provides the sighting, positioning (200 degrees azimuth and 60 degrees elevation), and firing the gun.
The GPU-2A gun pod can be utilized by the AH-1, helicopter. The GPU-2A is a self contained gun pod that mates the M-197 20mm auto-matic gun to a single ended linkless ammunition handling system, with a capacity of 300 rounds of linkless M-50 or PGU series 20mm electrically primed ammunition. The gun pod is self contained in that it houses a battery and gun control assembly which maintains the electrical power requirements well within capabilities of the parent aircraft. The GPU-2A is remotely fired utilizing cockpit controls to the gun control assembly in the gun pod. This allows a selectable rate of fire of either 750 or 1500 rounds per minute. The M61 Vulcan was modified into a lighter three-barrel version by removing three of the barrels, shortening the barrels, and changing the ammunition feed mechanism. The light weight modified Vulcan was type classified as the M197 20mm automatic gun. A modified Vulcan was also pintle mounted for use as a door gun on the UH-1 series "Huey" utility helicopter. The M97 series armament subsystem, with the M197 20mm cannon mounted on the 20mm/30mm universal turret system, replaced the M28 series armament subsystem on the AH-1 series "Huey" Cobra. The M97 series aircraft armament subsystem was used on the Upgunned AH-1S and AH-1S Modernized Cobras. The M97A4 is used on the current configuration AH-1F Modernized Cobra.
