The Joint Strike Fighter (JSF) project emerged from several separate US and British projects undertaken during the 1980s and early 1990s, aimed at finding replacements for the A-10/OA-10 Thunderbolt II, the F-16 Fighting Falcon, the F/A-18 Hornet and AV-8B Harrier II as well as Britain’s Harrier GR series and the now retired Sea Harrier. Budgetary constraints and unreliable technology led to the cancellation of these projects and the two countries began looking to collaborate on an entirely new fighter design.

JAST was renamed the JSF in 1996. The JSF Concept Demonstration Phase (CDP) required the competitors to each develop and build a single-seat CTOL and a STOVL demonstrator. Lockheed Martin was awarded a US$719 million (EUR468 million, £362 million) contract for the CDP, while Boeing received US$662 million (EUR431 million, £334 million). The UK contributed some US$200 million (EUR130 million, £101 million), mostly towards engine development.

As with the original JAST/JSF requirement, the F-35 Lightning II will be available in three different versions. It is aimed that all three variants will share 70–90 per cent commonality in an effort to keep costs down.

• F-35A: CTOL variant for the USAF
• F-35B: STOVL variant for the USMC and the UK
• F-35C: CV variant for the US Navy

The first flight of the pre-production F-35A (AA-1) took place at Fort Worth on 15 December 2006. The first static model (AG-1) is available for ground testing. Further flight testing of AA-1 was delayed in May 2007 when the aircraft suffered from an electrical power failure as well as problems with the F135 powerplant. Testing resumed in August and as of April 2008, AA-1 had flown 40 flights. The first weight-optimised production-type F-35A (AF-1) will fly in 2009 with a further
production-type model (AF-2) to be delivered in 2010 specifically to test the aircraft’s flight capabilities. Further F-35A models will then be tasked with testing the aircraft’s mission systems, prior to the start of FRP in 2015. Assembly of the first production F-35A for the USAF, currently codenamed AF-6, began in 2007 with Northrop Grumman announcing that it had begun work assembling the centre fuselage at its Palmdale Manufacturing Centre.

The first F-35B (BF-1) is due to make its maiden flight in late May/June 2008. Initial STOVL testing will take place at a specially-constructed 160 ft (54.9 m) x 80 ft (24.4 m) ground hover pit during BF-1’s first flights, although full STOVL flight testing is not expected to take place until early 2009 after Pratt & Whitney was forced to deliver a new modified
F135-PW-600 engine for BF-1 flight testing after the original engine suffered turbine blade failure. Initial F-35B deliveries to the USMC for training purposes are expected in 2011. The first F-35C prototype (CF-1) has been delayed until 2009 after the electrical power generator for the variant was found to be underpowered. The first static F-35C (CG-1) will begin ground testing in the same year.