There were heavy aircraft losses during the Vietnam War. Hundreds of U.S. fixed-wing aircraft were lost to ground fire of anti-aircraft artillery (AAA), surface-to-air missiles (SAMs), and fighter interceptors (MiG)s. The great majority of U.S. combat losses in all areas of Southeast Asia were to AAA. In 1972, Following the bombing of Hanoi and the North during Operations Linebacker 1 and Linebacker 2, North Vietnam announced that the 4,000 USAF planes had been shot down during the Second Indochina War / Vietnam War to date. The USA disputes this figure but concedes that during the course of the war the US Air Force flew 5.25 million sorties over South Vietnam, North Vietnam, northern and southern Laos, and Cambodia, losing 2,251 aircraft: 1,737 to hostile action, and 514 to operational causes. 110 of the losses were helicopters and the rest fixed-wing.