The original personnel who served as early door gunners aboard CH-21, UH-34, and UH-1 helicopters in Vietnam, were enlisted men, with a designated and specially trained crew chief serving as both the aircraft's maintenance manager and a door gunner.
For the majority of the Vietnam War, the principal weapon of the door gunner was a medium machine gun (MG), initially, a M1919A4 .30 calibre MG, and soon thereafter, the M60 7.62mm MG became the standard helicopter door armament system.
Initially, the door gunner's MG weapons were mounted on swivelling mounts (pintle mount) in order to retain and steady the door armament weapon. As the war progressed, using bungee cords to suspend/retain the MG became a common practice, as the newfound manoeuvrability of these "bungeed" weapons allowed for increased firing angles. However, some door gunners simply continued to hand-wield the weapon for a maximum level of manoeuvrability of fire.
Door gunners were normally restrained for safety within the aircraft, by either using a standard lap belt, or if the gunner wanted freedom of movement within the aircraft while still being retained, he used a monkey harness, which was a GI safety harness worn on the torso, and anchored to the aircraft floor, or cabin wall. The monkey harness allowed a door gunner great movement, including to lean outward on the helicopter skids, to get a better firing angle.
The door gunner position was not a particularly popular one, due to the exposed position of manning a machine gun in the open door of a helicopter. According to popular legend, the door gunner on a Vietnam era Huey gunship had a lifespan of 5 minutes!