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From when it first flew until around the time that its production ended, the CH-37 Mojave, designated the S-56 by Sikorsky, was the largest helicopter outside of the Soviet Union. It was also the largest U.S. military helicopter until the end of 1961.
The CH-37 Mojave was the first twin engine helicopter produced by Sikorsky. Although lighter and more powerful turboshaft engines had already been developed, Sikorsky used Pratt & Whitney R-2800 radial piston engines to power the helicopter.
At the time the CH-37 was built, it was felt that the radial engine was more reliable. The R-2800 chosen by Sikorsky had powered a number of fixed wing aircraft with great success.
The primary mission of the CH-37 was as an assault transport for the U.S. Army, USMC and U.S. Navy. The army originally designated the helicopter as the CH-37 Mojave, the marines as the HRS-1, while the navy designated it the HR2S.
The CH-37 was unique for its time in that in addition to having two engines they drove a five blade main rotor and a four blade anti-torque tail rotor. Other large helicopters of the time used tandem rotors fore and aft.
Also unique for the time were the retractable landing gear of the CH-37. Its twin wheel main landing gear retracted rearward into the engine nacelles.
CH-37 helicopters provided the U.S. armed services with a lift capacity never seen before. Clam shell front doors and a loading ramp enabled straight-in loading. Due to its engines being outside of the fuselage in separate nacelles, more room was available inside. The CH-37 could hold up to three army jeeps, 24 stretchers, or 26 fully equipped combat soldiers. Its winch could lift up to 2,000 lbs.
In 1956 the CH-37 Mojave set a then world record by carrying a payload of 13,250 lbs. to an altitude of 7,000 feet.
Army CH-37 Mojave helicopters were deployed with the 4th Medium Helicopter Transportation Co. in February of 1958.
In 1959 the CH-37 was deployed overseas for the first time with the U.S. Army to Germany.
In 1963 the CH-37 was deployed to Vietnam where it performed search and rescue duties, particularly recovering aircraft from difficult to access areas.
The Sikorsky CH-37 Mojave was retired from military service by 1969. A total of 154 CH-37 helicopters of all types were produced.