The United States Army issued a request for proposals (RFP) for its Advanced Aerial Fire Support System (AAFSS) program on 1 August 1964.

[2] Sikorsky submitted the S-66, which featured a "Rotorprop" serving as a tail rotor but as speeds increased would rotate 90° to act as pusher prop.

The Army perceived Lockheed's design as less expensive, able to be available earlier, and that it would have less technical risk than Sikorsky's Rotorprop.

After further AAFSS problems, the company developed an intermediate, high-speed attack aircraft named the Sikorsky S-67 Blackhawk in 1970.

To reduce drag at high speed, the main wheels retracted fully into the stub wing sponsons.

[3] The S-67 was fitted with a moving map display, a hands-on-collective radio tune control, and night vision systems.

Instead, the Army chose to create the new Advanced Attack Helicopter program, which would lead to the AH-64 Apache several years later.

As part of internal Sikorsky R&D efforts, in 1974, the S-67 had a 3.5-foot-diameter (1.1 m) ducted fan fitted instead of its original conventional tail rotor.

The lone S-67 prototype crashed while conducting a low-level aerobatic demonstration at the Farnborough Airshow on 1 September 1974.