In May 1958, Sikorsky began work on an experimental flying crane helicopter, the S-60, derived from the S-56 (HR2S-1 / H-37 Mohave) heavy-lift helicopter. The S-60 inherited the S-56s rotor system and twin power modules, each with a Pratt & Whitney (P&W) R-2800 Double Wasp radial piston engine, but had a stripped-down fuselage with long taildragger landing gear that allowed it to straddle cargoes. The crew operated from a glassed-in nose module; the copilot could swing his seat around to face the back to keep an eye on sling loads, controlling the helicopter in this position with an alternate set of controls. The S-60 had an automatic stabilization system to allow it to hover precisely, using inputs from a sidestick controller. The S-60 performed its first flight on 25 March 1959. The S-60 was lost in a crash in April 1961, but by that time the prototype for the turboshaft-powered S-64 Skycrane was already being built.