The role of "door gunner" originated during the Vietnam War, when helicopters were first used in large numbers. The original personnel who served as door gunners aboard UH-34 and UH-1 helicopters were normally enlisted crew chiefs who served as both the aircraft's maintenance supervisor and the door gunner. Later, as the War progressed, the door gunner position usually became a non-aviation soldier or Marine that volunteered for door gunner duties. Thus, most aircraft carried both a crew chief and door gunner, with the crew chief manning a weapon as well. Initially, door gunners' weapons were mounted on swiveling mounts in order to aim and steady the weapon, usually an M60 Machine gun. As the war progressed, using bungee cords to suspend the weapons became a common practice for door gunners, as the newfound manuverablility of the mounted weapons allowed for increased angles to shoot from. Safety lines were also attached to the door gunners to prevent them from falling out of the helicopter if the door gunners leaned outward on the helicopter skids to get a better firing angle.