fixed mountings in bombers and ground attack aircraft like the Douglas SBD Dauntless dive bomber, Grumman TBF Avenger torpedo bomber, and medium bombers such as North American B-25 Mitchell, Martin B-26 Marauder, and Douglas A-26 Invader; usually 4–8 per aircraft but the bombers could mount 12 or more in certain configurations. The later, faster-firing electrically feed-boosted AN/M3 was used in many Korean War–era USAF fighter aircraft such as the Lockheed F-80 Shooting Star, Republic F-84 Thunderjet, North American F-86 Sabre, and early versions of the Martin B-57 Canberra bomber. The US Navy had largely completed their move to the (unrelated) M2/AN 20mm autocannon for aircraft armament by this time. Turret-mount or flexible-mounted defensive armament, again only with the AN/M2 light-barrel version, in almost all US World War II–era bombers and patrol aircraft such as the Boeing B-17 Flying Fortress, Consolidated B-24 Liberator and Boeing B-29 Superfortress heavy bombers, North American B-25 Mitchell and Marin B-26 Marauder medium bombers, Consolidated PBY Catalina patrol flying boats, Goodyear K- and M-class blimps, Grumman TBF/TBM Avenger torpedo bombers, and in a combined offensive/defensive turret mounting in many Northrop P-61 Black Widow night fighters. The AN/M3 was used as a flexible, quad-mounted, radar-directed tail-defense gun as late as 1980 on the Boeing B-52 Stratofortress, until replaced by 20mm M61 Vulcan Gatling-type cannon on the H model. Variants of the AN/M3 are used as flexible door guns or as flexible remotely-controlled armament subsystems on many US Army, Navy, Marine Corps and Coast Guard helicopters, such as the Bell UH-1 Iroquois, Sikorsky UH-60 Blackhawk and variants, Sikorsky CH-53E Super Stallion, Bell OH-58 Kiowa, and others. United States At the outbreak of the Second World War, the United States had versions of the M2 in service as fixed aircraft guns, anti-aircraft defensive guns (on aircraft, ships, or boats), infantry (tripod-mounted) guns, and as dual purpose anti-aircraft and anti-vehicular weapons on vehicles. The .50 AN/M2 light-barrel aircraft Browning used in planes had a rate of fire of approximately 800 rounds per minute and was used singly or in groups of up to eight guns for aircraft ranging from the P-47 Thunderbolt to the B-25 Mitchell bomber, which in the last J-version of the Mitchell could have up to fourteen M2s firing forward for ground attack missions – eight in a solid metal-structure nose, four more mounted in a pair of conformal twin-gunned gun pods on the lower cockpit sides,