What was the most gun used by the Americans in the Vietnam War?

Answer 1

The WWII .45 Thompson submachine gun, M1 Garand, .30 & .50 caliber Browning machine guns, .45 pistol, and M1/M2 Carbines were all used from the beginning of the war in 1955 thru 1975 by the US and ARVNs.

The M14 US Rifle saw service for only about 2 or so years before being phased out by the M16 Jungle Rifle.

The M16 Jungle Rifle finally completely replaced the M14 service rifle in Vietnam ONLY by about 1968/69. The US Rifle M14 remained the general issue service rifle everywhere in the world for US forces until the 1970s (except South Vietnam). The M16 was specially designated for "jungle warfare only" until it completely replaced the M14.

Because so many M16s were issued to so many US servicemen during the war and at the height of the US troop ceiling (over half a million GIs in country by 1968 alone) the M16 would be the firearm mostly used in the Viet War.

Although the other previously mentioned firearms had been in use much longer than the M16, they weren't issued in the large numbers that the M16 was. So again, the M16 was used the most. Everybody had M16s, even helicopter pilots and door gunners had them strapped somewhere in their choppers like fire extinguishers.