05/31/2011. Remarks by Ray Watkins: "The S-61F was a compound helicopter test vehicle based on the airframe of an SH-3A Sea King which was funded jointly by Sikorsky and an Army/Navy contract awarded in 1964.

The fuselage was streamlined with the boat hull bottom faired over and the side floats removed. The tail rotor pylon with its half-span starboard side stabilizer was replaced with a larger tail fin unit, set at a lower angle to the tail boom, with a full-span stabilizer (made from Cessna T-37 components) at half height instead of just below the tip of the pylon.

Both the tail fin and the horizontal stabilizer had control surfaces. A 32 ft (9.75 m) wing was attached below the rotor head and a pair of 3,000 lb (1,361 kg) st Pratt & Whitney J60-P-2 turbojets were installed on the ends of stub wings below the main wing. The retractable main landing gear units were modified to store inside the hull.

The aircraft was intended to operate in various configurations; with or without the wing, with or without the supplementary engines and with five-blade or six-blade main rotors with high or low twist blades. The first flight occurred on May 21, 1965 with the turbojets and a low-twist five-blade rotor fitted. The test program of 113 flights and 88 hours was very successful, with a maximum speed of 255 mph (413 kmh) being obtained. The test program was terminated in May 1967."