On September 29, 1964, the first XC-142 prototype performed its first conventional flight, followed by its first hover on December 29 of the same year. On January 11, 1965, it took its first transitional flight. The aircraft was not able to pass on the prototype stage despite its successful capabilities, and only a total of five XC-142s were built.

The XC-142A can carry two crew members and thirty-two fully-equipped troops or twenty-four stretcher patients and four attendants or 3,600 kg of cargo. It has an external length of 17.70 meters, an external height of 3.85 meters, and a fuselage diameter of 2.6 meters. It is a tiltwing aircraft designed with a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff and landing. The wingspan is 20.57 meters and the wing area is 49.66 square meters. It has a tail height of 7.95 meters and a wheelbase of 7.9 meters. The aircraft has an empty weight of 10,249 kg, a gross weight of 15,637 kg (VTOL weight), and a maximum takeoff weight of 20,185 kg (STOL). The fuel tank capacity is 1,400 US gal.

The aircraft is powered by four General Electric T64-GE-1 turboprop engines. It is a free turbine turboshaft that features a high overall pressure ratio and low specific fuel consumption. It has a fourteen-stage high-pressure axial compressor, annular combustors, two-stage HP two-stage PT axial turbine, and a pressure spray oil system. Each engine produces a maximum power of 2,850 shaft horsepower and drives four-bladed Hamilton Standard variable-pitch 4.72 meter-diameter propellers.

The XC-142 has a maximum speed of 375 knots at 20,000 feet and a cruise speed of 250 knots at sea level. The combat range is 200 to 410 nautical miles and the ferry range is 3,300 nautical miles. The aircraft can fly up to 25,000 feet and can climb at a rate of 6,800 feet per minute.