Origins
In 1960, the United States Marine Corps began to seek a replacement for their HR2S piston-powered helicopters. On 27 January 1961, the Marine Corps began working with the other three U.S. armed services on the "Tri-Service VTOL transport", which would eventually emerge as the Vought-Hiller-Ryan XC-142A tiltwing. The design became more elaborate and the program stretched out, causing the Marines to drop out when they decided they would not receive a working machine in a satisfactory timeframe. In the end, the XC-142A, although a very innovative and capable machine, never entered production.
In March 1962, the US Navy's Bureau of Naval Weapons, acting on behalf of the Marines, issued a request for a "Heavy Helicopter Experimental / HH(X)". The specifications dictated a load capability of 8,000 pounds (3,600 kg) with an operational radius of 100 nautical miles (190 km; 120 mi) at a speed of 150 knots (280 km/h; 170 mph). The HH(X) was to be used in the assault transport, aircraft recovery, personnel transport, and medical evacuation roles. In the assault transport role, it was to be mostly used to haul heavy equipment instead of troops.
In response, Boeing Vertol offered a modified version of the CH-47 Chinook; Kaman Aircraft offered a development of the British Fairey Rotodyne compound helicopter; and Sikorsky offered what amounted to a scaled-up version of the S-61R, with twin General Electric T64 turboshafts and the dynamic system of the S-64, to be designated the "S-65". Kaman's proposal quickly died when the British government dropped its backing of the Rotodyne program. Competition between Boeing Vertol and Sikorsky was intense, with the Chinook having an advantage because it was being acquired by the United States Army. Sikorsky threw everything into the contest and was awarded the contract in July 1962.
The Marines originally wanted to buy four prototypes but ran into funding problems. Sikorsky, determined to keep the deal, cut their estimate for development costs and said that the program could be done with two prototypes. The military bought off on the proposal, and in September 1962 Sikorsky was awarded a contract for a little under US$10 million for two "YCH-53A" prototypes, as well as a mockup and a ground-test airframe.
The development program did not go entirely smoothly, due to a shortage of engineering resources plus various failures of subcontractors and the government, but these problems were gradually overcome. There was also the problem that U.S. Secretary of Defense Robert S. McNamara was pushing to maintain "commonality" between the armed services by using the Chinook, but the Marines managed to convince McNamara's staff that the Chinook could not meet their requirements without numerous expensive changes.
All these obstacles overcome, the first YCH-53A performed its initial flight at the Sikorsky plant in Stratford, Connecticut, on 14 October 1964, about four months behind schedule. The Marines had already placed an initial production contract for 16 helicopters in September. Flight trials went more smoothly than expected, helping make up for the lost time in development. It received the military designation and name "CH-53A Sea Stallion". Delivery of production CH-53s began in 1966.
Read more about this topic: Sikorsky CH-53 Sea Stallion, Development
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