Ground testing of the XFV-12A began in July 1977, and the aircraft was officially rolled out at the Rockwell International facility in Columbus, Ohio on 26 August. Due to increasing costs, construction of the second prototype was abandoned.
Tethered hover tests were conducted in 1978. Over the course of six months, it was determined that the XFV-12A design suffered from major deficiencies with regard to vertical flight, especially a lack of sufficient vertical thrust. Lab tests showed 55% thrust augmentation should be expected; however, differences in the scaled-up system dropped augmentation levels to 19% for the wing and a mere 6% in the canard. While the augmenters did work as expected, the extensive ducting of the propulsion system degraded thrust, and in the end the power-to-weight ratio was such that the engine was capable of vertically lifting only 75% of the weight of the aircraft in which it was mounted.
Following the tests, and with the program suffering from cost overruns, the Navy decided the XFV-12A was not worth further development, and cancelled the project in 1981. Aviation Week would later publish an article with drawings of an even more ambitious proposal to fit a similar wing to the huge Lockheed C-130 Hercules, but the plan never made it off the drawing board.
Of the two prototypes built, only one was completed, while the second prototype was cancelled.
The United States Marine Corps had adopted the British-designed Harrier, the only truly successful V/STOL design of the 1960s. Its replacement, the Lockheed Martin F-35 Lightning II, uses a shaft-driven fan and a swivelling rear nozzle to achieve vertical landing. It is designed for supersonic and vertical flight with performance just over Mach 1.5 with weapons and range comparable to the older F-4 and F-18.