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20mm Automatic Cannon



Image courtesy of Linford E. Riniker

Rate of Fire—650 to 850 Rounds per Minute (Typical 750 Rounds Per Minute).

Range—3,500 Meters Area Fire and 2,000 Meters Point Fire.

Muzzle Velocity—3,200 Feet Per Second.

Ammunition—M56 HEI (High-explosive Incendiary); M53 API (Armor-piercing Incendiary)

The M35 Armament System mounted a modified M61 Vulcan 20mm Automatic Cannon designated M195. With much shorter barrels than the M61, the rate of fire for the M195 had to be drastically reduced for helicopter use to 750 shots per minute from the Vulcan's normal rate of fire of 4,000 to 6,000 shots per minute, but even at that the vibration of the weapon was tremendous.


Introduced to Vietnam in late December 1969, the M35 armament system weighed in at 1,239 pounds fully loaded with 950 rounds. The ammo was delivered to the gun from two saddle ammunition containers affixed each side of the fuselage above the skids and connected by crossover feed chutes. Due to the explosive muzzle blast from the M195, extra plating had to be installed on the left side of the aircraft to protect the wiring, flight controls and fuselage.This weapon system provided Army aviation assets a long range suppressive fire system to counter .51 caliber Machineguns and other NVA anti-aircraft systems prevalent in South Vietnam areas of operation. The Centaurs had not made use of 20mm cannons until January 1972 when they accepted delivery of AH-1G 69-16439, a Cobra that obtained near legendary status as a Super Scout since deployed in 1970.


Centaur armorers left and right,
439 crew chief center,
in October/November 1972.
Image courtesy of Michael A. Peake.

The new Cobra 439 arrived in country in late 1969, for the 3rd Squadron, 17th Cavalry operating in the Pleiku region, configured with the M35, three 7-tube rocket pods and twin 7.62mm Miniguns in the nose turret. Under the command of CW2 Dave Tela, a three-time recipient of the Distinguished Flying Cross, the gunship saw extensive service in Cambodia during May/June 1970, and remained with the 17th Cavalry in the same configuration until transferred to Troop F, 4th Air Cavalry Centaurs in 1972.

20mm3The first modification the Centaur armorers made to 439 replaced the turret’s left hand minigun, prone to persistent jamming, with the M129 40 mm grenade launcher. To maximize effectiveness against NVA armor and light vehicles, including T54 and PT76 tanks, armorers altered the high explosive incendiary ammunition load for the 20mm with an armor piercing incendiary every third round.

Image courtesy of Linford E. Riniker.


With the target rich environment diminishing by May 1972, 439 often returned with the right hand ammunition box at full capacity. From that time until the cease-fire, the aircraft flew missions with 500 rounds in the left-hand box. To compensate for the weight differential and to give the aircraft added punch, a 19-tube rocket pod replaced the 7-tube launcher mounted inboard right side.



Vietnam Choppers and Their Crews, Jonathan Bernstein/Gordon Rottman, Osprey Publishing Ltd. (2007).

Vietnam Order of Battle, Shelby L. Stanton, U. S. News Books (1986).