The X-35 was declared the winner over the competing Boeing X-32 and a developed, armed version went on to enter production in the early 21st century as the F-35 Lightning II.

It is the smallest and lightest version, and is intended primarily to replace the U.S. Air Force's aging F-16 Fighting Falcons and A-10 Thunderbolt IIs.

The U.S. Marine Corps will use the F-35B to replace both its AV-8B Harrier IIs and F/A-18 Hornets with a design similar in size to the Air Force F-35A, trading fuel volume for vertical flight systems.

The U.S. Navy initially planned to purchase 480 JSF; this number was eventually revised to 260 aircraft, with an additional 80 for the U.S. Marine Corps.

The levels generally reflect the financial stake in the program, the amount of technology transfer and subcontracts open for bid by national companies, and the priority order in which countries can obtain production aircraft.

[15] Both the X-32 and X-35 power plants were derived from Pratt & Whitney's F119, with the STOVL variant of the latter incorporating a Rolls-Royce Lift Fan module.

The turbofan acted somewhat like a turboshaft engine embedded into the fuselage (but with a much smaller percentage of total heat energy being extracted by the turbine stage).

[19] A portion of engine power was extracted via a turbine, and used to drive a shaft running forward via a clutch-and-bevel gearbox to a vertically mounted, contra-rotating lift fan.

Though risky and complicated, it was made to work to the satisfaction of DoD officials, and flight testing of the X-35 demonstrators reduced risk to Technology Readiness Level 6.

After 28 test flights, the aircraft was converted to the X-35B, which added the shaft-drive lift fan, aft swivel nozzle, and roll posts.

It now resides at the National Air and Space Museum Steven F. Udvar-Hazy Center, near Washington Dulles International Airport in Virginia.

[30] Data from Air Force Magazine,[31] Aviation Week & Space Technology,[32][33] Flight International,[34] Aerospace America[35]General characteristics Performance Related development Aircraft of comparable role, configuration, and era