The "Credible Sport" phase I program was initiated by the OSD directorate and was designed to validate S.T.O.L. approach configuration and associated avionics. Hercules 74-1683 was modified so it could take off and land almost like a helicopter. The aircraft was equipped with lift rockets slanting downward, slowdown rockets facing forward. The aircraft was intended for use in Iran to rescue American hostages. During a STOL demonstration flight the pilot fired the upper set of slowdown rockets at a height of 40 feet, instead of 20 feet at usual. The navigator was trained to fire the lower slowdown rockets three seconds later, just after touchdown.