The Joint Strike Fighter on show at Australian International Airshow

In 1993, the Defense Advanced Research Projects Agency executed a program to develop a supersonic Short Take-Off and Vertical Landing (STOVL) aircraft as a replacement for the AV-8B Harrier. At about the same time, the Department of Defense (DoD) considered canceling the Navy's Advanced Attack/Fighter (A/F-X) that was being studied to fill the void left after the cancellation of the General Dynamics/McDonnell Douglas A-12 Avenger II aircraft being designed for the U.S. Navy.

Senior leadership at the Pentagon suggested a Joint Attack Fighter (JAF) to replace the Navy's A/F-X program. Not only would the JAF be much cheaper than the A/F-X, it would also be designed with a common airframe suitable to the three services. It was believed that such an aircraft would herald significant manufacturing and operational cost savings. Much of the philosophy surrounding the JAF would later be incorporated into JAST, such as its single-engine design and its unprecedented level of commonality.

The Joint Advanced Strike Technology (JAST) Program was initiated in late 1993 as a result of the DoD Bottom-Up-Review (BUR). The major tactical aviation results of the BUR were to continue the ongoing F-22 and F/A-18E/F programs, cancel the Multi-Role Fighter (MRF) and the A/F-X programs, curtail F-16 and F/A-18C/D procurement and initiate the JAST Program.

The JAST program office was established on 27 January 1994. Its mission was to define and develop aircraft, weapon, and sensor technology that would support the future development of tactical aircraft. The program subsequently moved from a broad, all-encompassing program to one that would develop a common family of aircraft to replace several aging US and UK aircraft.

By the end of 1994, the JAST program had absorbed the DARPA Common Affordable Lightweight Fighter (CALF) program. CALF, then renamed ALF, became the primary focus of JAST. However, JAST was also considering modifying the CTOL versions of the aircraft to perform in a STOVL role. Congress subsequently mandated the merger of JAST with the DARPA Advanced Short Take-Off / Vertical Landing program. As JAST was already considering STOVL variants, this merger was accommodated with comparatively little disruption. The JAST Program initially explored a wide range of potential strike warfare concepts using six-month, Concept Exploration (CE) study contracts awarded in May 1994.

The findings of the CE studies showed that a "tri-service family" of aircraft was the most affordable solution to the collective joint-service needs. The tri-service family would entail a single basic airframe design with three distinct variants: Conventional Take-Off and Landing (CTOL) for the U.S. Air Force to complement the F-22 Raptor and replace the aging F-16 Fighting Falcon and the A-10 Thunderbolt; Short Take-Off/Vertical Landing (STOVL) for the U.S. Marine Corps to replace both the AV-8B Harrier and the F/A-18 C/D Hornet; and a Carrier (CV) variant for the U.S. Navy to complement the F/A-18 E/F Super Hornet.

Following numerous trade studies, two critical decisions were made: the JAST family of aircraft would be single-crew and single-engine. Navy attack/fighter aircraft have been preferred to have two engines in case one is lost during flight. The choice of a single-crew aircraft was accepted - subject to continued studies and appropriate technology maturation - on the projection that a single crewmember could perform all of the intended missions.

Boeing, Lockheed Martin, McDonnell Douglas, and Northrop Grumman were each awarded fifteen-month Concept Definition and Design Research (CDDR) contracts in December 1994. Northrop Grumman and McDonnell Douglas/British Aerospace teamed shortly after the CDDR contracts were awarded. The contractors refined their Preferred Weapons System Concept (PWSC) designs and performed a number of risk reduction activities (e.g., wind tunnel tests, powered-model STOVL tests, and engineering analyses).

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