The Sikorksy S-64 was designed as an enlarged version of the prototype flying crane helicopter, the Sikorsky S-60. The S-64 had a six-blade main rotor and was powered by two 4,050 shaft horsepower (3,020 kW) Pratt & Whitney JFTD12A turboshaft engines. The prototype S-64 first flew on May 9, 1962 and was followed by two further examples for evaluation by the German armed forces. The Germans did not place an order, but the United States Army placed an initial order for six S-64A helicopters (with the designation YCH-54A Tarhe). Seven S-64E variants were built by Sikorsky for the civil market.