Sikorsky S-61 Helicopter. In September 1957 the US Navy awarded Sikorsky a development contract to produce an amphibious anti submarine warfare helicopter capable of detecting and attacking submarines. The prototype Sea King flew on March 11 1959, while production deliveries took place from September 1961. Power for initial production aircraft was supplied by two 930kW (1250shp) General Electric T58GE8B turboshafts.
Development of a civil version was undertaken almost concurrently, with the commercial S61L flying for the first time on November 2 1961. While based on the Sea King, the S61L is 1.27m (4ft 3in) longer allowing it to carry a substantial payload of freight or passengers. Power for initial production S61Ls was supplied by two 1005kW (1350shp) GE CT58140 turboshafts, the civil equivalent of the T58.