UK/Italy/Japan aircraft development and acquisition programme
The Global Combat Air Programme (GCAP; ; ) is a multinational initiative led by the United Kingdom, Japan, Italy to jointly develop a sixth-generation stealth fighter. The programme aims to replace the Eurofighter Typhoon in service with the Royal Air Force (RAF) and Italian Air Force, and the Mitsubishi F-2 in service with the Japan Air Self-Defense Force. 
On 9 December 2022, the governments of Japan, the United Kingdom, and Italy jointly announced that they would develop and deploy a common fighter jet, merging their previously separate sixth-generation projects: the United Kingdom-led BAE Systems Tempest developed with Italy, and the Japanese Mitsubishi F-X. This was cemented with a treaty signed in December 2023 in Japan.
There are around 9,000 people working on the programme worldwide, with 1,000 and more suppliers from across the three partner nations. 600 such suppliers are based in the UK, and 400 are based in Italy and Japan. 
Under the current timeline, the programme expects to begin the formal development phase from 2025, with a demonstrator aircraft to fly in 2027, and production aircraft to begin entering service from 2035.
Background.
United Kingdom &amp; Italy (Tempest).
On 16 July 2018 during the Farnborough Airshow, a mock-up of 'Tempest' was presented, a BAE Systems led sixth-generation fighter programme and wider Future Combat Air System (FCAS) that would be developed to replace the RAF's Eurofighter Typhoons in the mid-to-late 2030s. This would be developed by an industrial consortium known as Team Tempest consisting of BAE, Rolls Royce, Leonardo, and MBDA working in conjunction with the Ministry of Defence and the Royal Air Force's Rapid Capabilities Office. 
On 19 July 2019, Sweden signed a Memorandum of understanding (MoU) with the UK to work together in developing the wider FCAS needed for the future of aerial operations. on 11 September during DSEI 2019, Italy formally joined the Tempest programme. In 2020, Sweden and the UK 'firmed up' their MoU for FCAS and saw Sweden's SAAB establish a centre-of-excellence in the UK as part of a £50 million investment, However it was stressed that this was not an indication that Sweden or SAAB had signed onto the main Tempest effort. On the 21 December 2021, The UK, Italy, and Sweden signed a trilateral MoU for cooperation on the FCAS.
A number of new technologies were being explored for Tempest, including:
Much of the technology envisioned for use on Tempest would initially be fielded on 'Excalibur', a Boeing 757-200 modified by British firm 2Excel in conjunction with Leonardo UK to serve as a test aircraft. The aim of Excalibur is to de-risk and validate the technologies being examined for the fighter including testing the aerodynamics of the fighter's nose section and testing the aircraft's sensor suite. This development would also continue with a demonstrator aircraft announced in 2022 which is expected to take flight around 2027.
It was envisaged that the programme would agree to funding and manufacturing arrangements by 2025 with an expected in-service date for the aircraft in 2035.
Japan (F-X).
Japan, an island nation, has a disproportionately vast air defence identification zone given the size of its land territory, and it was expected that the country would have to protect it with a smaller fleet of fighters compared to those of its growing neighbours with much larger populations. To address this issue, the Ministry of Defence decided in 2010 that Japan's next-generation fighter had to be highly information-based, intelligent, and capable of instantaneous response (i3 fighter). At the time, the fighter fleet of the Japan Air Self-Defence Force mainly consisted of the Mitsubishi F-15J and the Mitsubishi F-2. The former is a variant of the F-15, manufactured by Mitsubishi Heavy Industries (hereafter referred to as Mitsubishi) under licence, while the latter was developed by Mitsubishi and Lockheed Martin based on the F-16 in the 1990s. While the F-15J was set to be replaced by the F-35, a replacement for the F-2 needed to be found before its planned retirement in the 2030s.
Following the USA's decision not to allow the export of the F-22 Raptor to any other country in 2007, Japan began looking for a domestic solution to field a new fighter aircraft to replace its Mitsubishi F-2 fleet. From the mid-2000s Japan began funding various research programmes involved in fighter design culminating in the Mitsubishi X-2 Shinshin experimental aircraft which took flight on 22 April 2016. This research and the data collected from the X-2 programme would feed the development of Japan's main fighter effort, the Mitsubishi F-X programme. The IHI Corporation completed a prototype for the XF9 engine in 2018. In 2018, after more than a decade since America's refusal to export the F-22, Lockheed Martin proposed a potential Japan-America collaboration project to develop the F-2 successor based on the F-22 and F-35, but this was rejected by Japan. 
Development.
Discussions for both parties combining their respective fighter development efforts as a means of reducing their overall development costs began as early as 2017. In December 2021, the first results of this endeavour appeared when the UK and Japan announced they would jointly cooperate to produce a demonstrator for a new fighter engine as well as the signing of a memorandum of cooperation to explore future air combat technologies together. On 15 February 2022, a further agreement was reached between both nations to jointly develop sensor capabilities for their respective fighters known as the 'Japan and Great Britain Universal Advanced RF (radio-frequency) system' or 'JAGUAR'. 
In July 2022, Reuters reported from anonymous sources within both programmes that both parties were close to a deal that would combine both Tempest and F-X into a single joint programme. On 9 December 2022, this was proven correct when it was officially announced by British Prime Minister Rishi Sunak that the Tempest and F-X programmes would merge into a single endeavour to procure a common multi-role fighter now called the "Global Combat Air Programme" (GCAP). The resulting aircraft would also be expected to be available for export to further reduce the per-unit costs. 
The programme is envisaged as an equal partnership between the member nations. In the UK, BAE Systems will act as prime contractor and handle the airframe, Rolls-Royce the engines, Leonardo's UK division the electronics, and MBDA UK the weapons. In Japan, Mitsubishi Heavy Industries will act as prime contractor, with IHI Corporation handling the engines, and Mitsubishi Electric handling the electronics. In Italy, Leonardo S.p.A. will be prime contractor, with Avio Aero working on the engines, and MBDA IT will also work on missile development. By around 2024, detailed development and cost sharing for each company will be clarified, and production will begin around 2030, with the first aircraft to be deployed in 2035.
Possible Swedish, Saudi Arabian, and German membership.
In late December 2022, two weeks after GCAP was announced, Japan and Sweden signed an ‘Agreement on the Transfer of Defence Equipment and Technology' that would explore deeper bilateral ties between both nations. This also began speculation as to Sweden potentially becoming a member of GCAP as a means of replacing their Saab JAS 39 Gripen given that Sweden had previously been cooperating with the UK and Italy regarding the FCAS to which Tempest would have contributed. However, in March 2023, several industrial figures involved in GCAP placed doubt on Sweden joining GCAP with some stating that Sweden's concepts for FCAS did not align with the views of the UK or Italy.
On 11 August 2023, the "Financial Times" reported that Saudi Arabia was pushing to join the programme. While the UK and Italy were reportedly open to the concept, Japan was firmly opposed, seeing Saudi membership as a complication to both further domestic efforts in allowing Japanese defence exports to foreign nations and to the overall timeline for the programme in successfully producing an in-service aircraft by 2035. There were also concerns from defence sources that the security of sensitive technology might be complicated by Saudi membership as well as the questionable technical contribution that the Kingdom could feasibly provide to the programme.
On 15 September, Leonardo's CEO said that Saudi Arabia would not become a core partner in GCAP, with Reuters reporting that in a response to the question of Saudi membership they said "The programme is (for) UK, Japan, Italy, that's it. There is nothing else at the moment".
On 1 November 2023, The Times reported that Germany was considering abandoning the €100 billion Future Combat Air System; also known by its French designation SCAF (a parallel European effort to field a sixth-generation fighter design alongside other systems) with other core members France and Spain, and would instead look to join GCAP. This was said to be due to ongoing problems within both the SCAF programme regarding intellectual property and industrial participation as well as tensions spilling over from other European programmes such as on matters of air defence and Germany's procurement of the F-35A. However, Shepard News reported that this leak might potentially be a German negotiating tactic to pressure France and Spain to concede to Germany's demands for the programme. There was also scepticism as to whether Germany would even be able to join GCAP, at least to the same level of membership they had within SCAF, especially given previous statements by GCAP industry heads.
In December 2023, a Swedish official during the International Fighter Conference announced that Sweden would not make a decision on a future fighter to replace the Gripen until 2031 following several national studies and related planning efforts. It was also mentioned that Sweden walked away from bilateral and trilateral discussions with the UK and Italy a year before, but did not expand on the reasons for this decision. Whilst such a decision does not rule-out future Swedish participation in GCAP, delaying membership in the programme would risk losing industrial influence over design requirements.
During the February 2024 World Defence Show in Saudi Arabia, Ahmad Al-Ohali, the governor of the Saudi government’s General Authority for Military Industries (GAMI) stated that the kingdom remained "very keen" on participating in GCAP but stressed that this can only happen if "localisation" can occur and that Saudi Arabian industries are meaningfully involved in the program. This is seen as part of a larger national effort to ensure that at least 50% of all defence expenditure is reinvested domestically by 2030.
In late July 2024, Leonardo chief executive Roberto Cingolani said he would be “personally very open” to Saudi Arabia joining if Britain decides to reduce its commitment, “especially if there were some reallocation of resources” after the UK’s new Labour government completes its defence spending review.
At the 2024 G20 Summit in Brazil, leaders from Italy, the UK, and Japan advanced discussions on GCAP, including the potential participation of Saudi Arabia. Italian Prime Minister Giorgia Meloni, British Prime Minister Keir Starmer, and Japanese Prime Minister Shigeru Ishiba focused on cooperation frameworks during the negotiations, addressing key issues such as cost-sharing and technology transfer. The talks are expected to conclude by the end of the year, with Italian Foreign Minister Antonio Tajani confirming that Saudi Arabia is likely to join the programme.
In December 2024, it was reported that the United Kingdom was approaching Australia for involvement in the programme.
Joint Venture and Corporate Structure.
GCAP international Government Organisation.
On 12 September 2023, a trilateral collaboration agreement was signed between all three parties to support the long-term working arrangements and capability requirements of the programme. Three months later, on 14 December 2023, and twelve months after the initial agreement to pursue GCAP, the tri-lateral effort was cemented with the signing of an international treaty for the development of the aircraft in Tokyo. This treaty would see both the collaborative governmental headquarters and industrial hub for the effort be based in the UK, confirming earlier reports, with Japan providing the first CEO and Italy the first leader of the business entity. This would culminate in the formation of the GCAP international Government Organisation (GIGO) which would be responsible for managing the development of the fighter once the nations' respective political bodies gave their approval. The Defense of Japan 2024 white paper outlined that the GIGO would first see technical officials dispatched as technology experts and a sophisticated and secure working environment established to ensure a smooth and reliable development process for the aircraft. Meeting with the various companies and industries contributing to the programme as well consultations with representatives of