The United States principally funds F-35 development, with additional funding from other NATO members and close U.S. allies, including the United Kingdom, Italy, Australia, Canada, Norway, Denmark, the Netherlands, and Turkey. These funders generally receive subcontracts to manufacture components for the aircraft; for example, Turkey is the sole supplier of several F-35 parts. Several other countries have ordered, or are considering ordering, the aircraft.
As the largest and most expensive military program ever, the F-35 became the subject of much scrutiny and criticism in the U.S. and in other countries. In 2013 and 2014, critics argued that the plane was "plagued with design flaws", with many blaming the procurement process in which Lockheed was allowed "to design, test, and produce the F-35 all at the same time," instead of identifying and fixing "defects before firing up its production line". By 2014, the program was "$163 billion over budget [and] seven years behind schedule". Critics also contend that the program's high sunk costs and political momentum make it "too big to kill".
The F-35 first flew on 15 December 2006. In July 2015, the United States Marines declared its first squadron of F-35B fighters ready for deployment. However, the DOD-based durability testing indicated the service life of early-production F-35B aircraft is well under the expected 8,000 flight hours, and may be as low as 2,100 flight hours. Lot 9 and later aircraft include design changes but service life testing has yet to occur. The U.S. Air Force declared its first squadron of F-35As ready for deployment in August 2016. The U.S. Navy declared its first F-35Cs ready in February 2019. In 2018, the F-35 made its combat debut with the Israeli Air Force.
The U.S. stated plan is to buy 2,663 F-35s, which will provide the bulk of the crewed tactical airpower of the U.S. Air Force, Navy, and Marine Corps in coming decades. Deliveries of the F-35 for the U.S. military are scheduled until 2037 with a projected service life up to 2070.
F-35 development started in 1992 with the origins of the Joint Strike Fighter (JSF) program and was to culminate in full production by 2018. The X-35 first flew on 24 October 2000 and the F-35A on 15 December 2006.
The F-35 was developed to replace most US fighter jets with the variants of a single design that would be common to all branches of the military. It was developed in co-operation with a number of foreign partners, and, unlike the F-22 Raptor, intended to be available for export. Three variants were designed: the F-35A (CTOL), the F-35B (STOVL), and the F-35C (CATOBAR). Despite being intended to share most of their parts to reduce costs and improve maintenance logistics, by 2017, the effective commonality was only 20%. The program received considerable criticism for cost overruns during development and for the total projected cost of the program over the lifetime of the jets.
By 2017, the program was expected to cost $406.5 billion over its lifetime (i.e. until 2070) for acquisition of the jets, and an additional $1.1 trillion for operations and maintenance. A number of design deficiencies were alleged, such as: carrying a small internal payload; performance inferior to the aircraft being replaced, particularly the F-16; lack of safety in relying on a single engine; and flaws such as the vulnerability of the fuel tank to fire and the propensity for transonic roll-off (wing drop). The possible obsolescence of stealth technology was also criticized.