[1] The project's purpose was to develop a stealth-enabled design to replace all of United States Department of Defense lighter weight fighter and attack aircraft, including the F-16 Fighting Falcon, McDonnell Douglas F/A-18 Hornet, and vertical/short takeoff / vertical landing (V/STOL) AV-8B Harrier II.

[4][5] Many companies took part in the first phase of this project, which involved drafting concept aircraft designs for submission to the Department of Defense.

This limitation promoted the adoption of low cost manufacturing and assembly techniques, and also prevented either Boeing or Lockheed Martin from bankrupting themselves in an effort to win such an important contest.

[citation needed] Boeing's strategy for a competitive advantage was to offer substantially lower manufacturing and life-cycle costs by minimizing variations between the different JSF versions.

[8] However, this choice required the engine to be mounted directly behind the cockpit, and moved the center of gravity forward from its usual position in jet fighters (towards the rear of the airplane) to enable a neutral-attitude hover.

Boeing had proposed, in the 1960s, a similar supersonic fighter with a mid-center-of-gravity mounted engine with vectored thrust nozzles, but this never proceeded beyond pictures published in Aviation Week.

[citation needed] By comparison, the Lockheed entry looked like, if anything, a smaller version of the F-22 Raptor stealth fighter.

This was required to feed sufficient air to the main engine (to provide the thrust necessary to hover) during the zero horizontal velocity phase, when it could not exploit ram-air pressure.

Mitigation possibilities included variable baffles designed to block incoming radio waves without adversely affecting airflow.

However, eight months into construction of the concept demonstrator aircraft, the JSF's maneuverability and payload requirements were refined at the request of the Navy and Boeing's delta wing design fell short of the new targets.

[12] After having the Pratt & Whitney F119 engine installed in April 2000, the X-32A commenced low- and medium-speed taxi tests, which had been completed by late May.

By contrast, the Lockheed Martin X-35 concept demonstrator aircraft were capable of transitioning between their STOVL and supersonic configurations in mid-flight.

[8] The first flight of the X-32A (designed for CTOL and carrier trials) took place on 18 September 2000, from Boeing's Palmdale plant to Edwards Air Force Base.

However, in the STOVL mode a butterfly valve diverted the core stream exhaust gases to a pair of thrust vectoring nozzles located close to the aircraft's center-of-gravity.

[22] Prior to the awarding of the contract, many lawmakers pushed the idea of retaining the losing competitor as a sub-contractor; however, the "winner takes all" principle was not changed.