The Sikorsky CH-37 Mojave (company designation S-56) is an American large heavy-lift helicopter of the 1950s. The S-56 came into being as an assault transport for the United States Marine Corps (USMC), with a capacity of 26 fully equipped Marines. An order for the aircraft was placed in 1951 using the U.S. Navy/U.S. Marine Corps designation of the time of HR2S. The first prototype, the XHR2S-1 flew in 1953 and production deliveries of the HR2S-1 began in July 1956 to Marine Helicopter Squadron One (HMX-1), with a total of sixty aircraft being produced. The United States Army evaluated the prototype in 1954 and ordered 94 examples as the CH-37A, the first being delivered in summer 1956. All Marine Corps and Army examples were delivered by mid-1960. Army examples were all upgraded to CH-37B status in the early 1960s, being given Lear auto-stabilization equipment and the ability to load and unload while hovering. In the 1962 unification of United States military aircraft designations, the USMC examples were redesignated from HR2S-1 to CH-37C. At the time of delivery, the CH-37 was the largest helicopter in the Western world and it was Sikorsky's first twin-engine helicopter. Two Pratt & Whitney R-2800 Double Wasp radial engines were mounted in outboard pods that also contained the retractable landing gear. This left the fuselage free for cargo, which could be loaded and unloaded through large clamshell doors in the nose. The early models could carry a payload of either three M422 Mighty Mites (a lightweight jeep-like vehicle) or 26 troops. For storage, the main rotor blades folded back on the fuselage and the tail rotor mast folded forward on the fuselage. The CH-37 was one of the last heavy helicopters to use piston engines, which were larger, heavier and less powerful than the turboshaft engines subsequently employed in later military helicopters. This accounted for the type's fairly short service life, all being withdrawn from service by the late 1960s, replaced in Army service by the distantly related CH-54 Tarhe and in the Marine Corps by the CH-53 Sea Stallion. Four CH-37Bs were deployed to Vietnam in September 1965 to assist in the recovery of downed U.S. aircraft, serving in this role from Marble Mountain Air Facility until May 1967.[2] They were very successful at this role, recovering over US$7.5 million worth of equipment, some of which was retrieved from behind enemy lines. The CH-37 was also used to recover film capsules descending from space by parachute. Variants XHR2S-1 Prototype Assault Transport for the US Marine Corps, powered by two 1,900 hp (1,400 kW) R-2800-54 engines, four built. HR2S-1 Production model for USMC with modified engine nacelles, twin mainwheels and dorsal fin, redesignated CH-37C in 1962, 55 built (order for additional 36 cancelled). HR2S-1W Airborne early warning aircraft for the US Navy, two built. YH-37 One HR2S-1 helicopter evaluated by the US Army. H-37A Mojave Military transport version of the HR2S for the US Army, changes included dorsal fin and modified rotor head fairing, redesignated CH-37A in 1962, 94 built. H-37B Mojave All but four of the H-37As were modified with a redesigned cargo door, automatic stabilization equipment and crashproof fuel cells. Later redesignated CH-37B. CH-37A H-37A redesignated in 1962. CH-37B H-37B redesignated in 1962. CH-37C HR2S-1 redesignated in 1962. S-56 Sikorsky company designation for H-37.
