The H-21 was originally developed by Piasecki as an Arctic rescue helicopter. The H-21 had winterization features permitting operation at temperatures as low as −65 °F (−54 °C), and could be routinely maintained in severe cold weather environments.
French service in the Algerian WarIn 1956, seeking a way to use helicopters in a ground attack role in the Algerian War, the French Air Force and French Army Aviation (ALAT, Aviation Légère de l'Armée de Terre) experimented with arming the Sikorsky S-55, then being superseded in service by the more capable Piasecki H-21 and Sikorsky H-34 helicopters. Some French Air Force and Army aviation H-21C helicopters were subsequently armed with fixed, forward-firing rockets and machine guns. A few even had racks for bombs, but tests subsequently determined that the H-21C lacked the maneuverability and performance needed in the ground-attack role. The H-21C was far more successful as a troop transport, and most H-21Cs in service were eventually fitted with flexible door-mounted guns such as the .50 cal. (12.7 mm) Browning machine gun or the (ex-German) MG 151/20 20 mm aircraft cannon for defensive use when landing assault forces under fire.
Though the H-21 had been removed from the ground attack role, official U.S. Army evaluations at the time indicated that the type was actually more likely to survive multiple hits by ground fire than was the Sikorsky CH-34; this was assumed to be a consequence of the location and construction of the CH-34's fuel tanks. By the close of the Algerian War, troop-carrying H-21C helicopters were being used in concert with H-34 ground-attack helicopters in large-scale counterinsurgency operations.
U.S. Army operationsThe H-21C saw extensive service with the U.S. Army, primarily for use in transporting troops and supplies. On August 24, 1954, with the assistance of in-flight refueling provided by a U.S. Army U-1A Otter, a H-21C known as Amblin' Annie became the first helicopter to cross the United States nonstop. Various experiments were made by the Army in arming the H-21C as a gunship; some Shawnees were armed with flex guns under the nose, while others were fitted with door guns. One experimental version was tested stateside with a Boeing B-29 Superfortress .50 cal. remote turret mounted beneath the nose. The H-21C (later designated CH-21C) was first deployed to Vietnam in December 1961 with the Army's 8th and 57th Transportation Companies, in support of ARVN (Army Republic South Vietnam) troops. In Army aviation service, the CH-21C Shawnee could be armed with 7.62 mm (.308 in) or 12.7 mm (.50 in) flexible door guns. Relatively slow, the CH-21's unprotected control cables and fuel lines proved vulnerable to the enhanced threat posed by NVA and Viet Cong ground forces, which were increasingly well supplied with automatic small arms and heavy (12.7 mm) AA machine guns. The H-21, which was designed for cold weather operations, performed poorly in the hot weather of Vietnam. Despite being capable of carrying 20 passengers, it only carried 9 when operating in Vietnam. The shooting down of a CH-21 Shawnee near the Laotian-Vietnamese border with the death of four aviators in July 1962 were some of the U.S. Army's earliest Vietnam casualties. Despite these events, the Shawnee continued in service as the U.S. Army's helicopter workhorse in Vietnam until 1964 when it was replaced with the UH-1 Huey. In 1965, the CH-47 Chinook was deployed to Vietnam, and later that year, most CH-21 helicopters were withdrawn from active inventory in the U.S. Army and Air Force.
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