SEPECAT Jaguar GR.3 XX725
The Jaguar programme began in the early 1960s, in response to a British requirement (Air Staff Target 362) for an advanced supersonic jet trainer to replace the Folland Gnat T1 and Hawker Hunter T7, and a French requirement (ECAT or École de Combat et d'Appui Tactique, "Tactical Combat Support Trainer") for a cheap, subsonic dual role trainer and light attack aircraft to replace the Fouga Magister, Lockheed T-33 and Dassault Mystère IV. In both countries several companies tendered designs: BAC, Hunting, Hawker Siddeley and Folland in Britain; Breguet, Potez, Sud-Aviation, Nord, and Dassault from France. A Memorandum of Understanding was signed in May 1965 for the two countries to develop two aircraft, a trainer based on the ECAT, and the larger AFVG (Anglo-French Variable Geometry)
Cross-channel negotiations led to the formation of SEPECAT (Société Européenne de Production de l'Avion d'École de Combat et d'Appui Tactique – the "European company for the production of a combat trainer and tactical support aircraft") in 1966 as a joint venture between Breguet and the British Aircraft Corporation to produce the airframe. Though based in part on the Breguet Br.121, using the same basic configuration and an innovative French-designed landing gear, the Jaguar was built incorporating major elements of design from BAC – notably the wing and high lift devices.
Production of components would be split between Breguet and BAC, and the aircraft themselves would be assembled on two production lines; one in the UK and one in France, To avoid any duplication of work, each aircraft component had only one source. The British light strike/tactical support versions were the most demanding design, requiring supersonic performance, superior avionics, a cutting edge nav/attack system of more accuracy and complexity than the French version, moving map display, laser range-finder and marked-target seeker (LRMTS). As a result, the initial Br.121 design needed a thinner wing, redesigned fuselage, a higher rear cockpit, and after-burning engines. While putting on smiling faces for the public, maintaining the illusion of a shared design, the British design defacto departed from the French sub-sonic Breguet 121 to such a degree that it was for all intents and purposes a new design.
A separate partnership was formed between Rolls-Royce and Turbomeca to develop the Adour afterburning turbofan engine. The Br.121 was proposed with Turbomeca's Tourmalet engine for ECAT but Breguet preferred the RR RB.172 and their joint venture would use elements of both. The new engine, which would be used for the AFVG as well, would be built in Derby and Tarnos.
Previous collaborative efforts between Britain and France had been complicated – the AFVG programme ended in cancellation, and controversy surrounded the development of the supersonic airliner Concorde. Whilst the technical collaboration between BAC and Breguet went well, when Dassault took over Breguet in 1971 it encouraged acceptance of its own designs, such as the Super Étendard naval attack aircraft and the Mirage F1, for which it would receive more profit, over the Anglo-French Jaguar.
The initial plan was for Britain to buy 150 Jaguar "B" trainers, with its strike requirements being met by the advanced BAC-Dassault AFVG aircraft, with France to buy 75 "E" trainers (école) and 75 "A" single-seat strike attack aircraft (appui). Dassault favoured its own Mirage G aircraft above the collaborative AFVG, and in June 1967, France cancelled the AFVG on cost grounds. This left a gap in the RAF's planned strike capabilities for the 1970s at the same time as France's cancellation of the AFVG, Germany was expressing a serious interest in the Jaguar, and thus the design became more oriented towards the low-level strike role.
The RAF had initially planned on a buy of 150 trainers; however, with both TSR2 and P.1154 gone, the RAF were looking increasingly hard at their future light strike needs and realizing that they now needed more than just advanced trainers with some secondary counter insurgency capability. The RAF's strike line-up was at this point intended to consist of American F-111s plus the AFVG for lighter strike purposes. There was concern that both F-111 and AFVG were high risk projects and with the French already planning on a strike role for the Jaguar, there was an opportunity to introduce a serious backup plan for the RAF's future strike needs - the Jaguar.
While the RAF had initially planned to buy 150 trainers, the TSR2 and p.1154 were gone, and believing that both the US F-111 and AFVG were high-risk programs, and with the French already planning a strike role for their Jaguar, the MOD suddenly realized they were in bad need of a new light strike aircraft capable of delivering tactical nuclear weapons. As a result, by October 1970, the RAF's requirements had changed to 165 single-seat strike aircraft and 35 trainers.
The Jaguar was to replace the McDonnell Douglas Phantom FGR2 in the close air support, tactical reconnaissance and tactical strike roles, freeing the Phantom to be used for air defence. Both the French and British trainer requirements had developed significantly, and were eventually fulfilled instead by the Alpha Jet and Hawker Siddeley Hawk respectively. The French, meanwhile, had chosen the Jaguar to replace the Aeronavale's Dassault Étendard IV, and increased their order to include an initial 40 of a carrier-capable maritime version of the Jaguar, the Jaguar M, for the Aeronavale. From these apparently disparate aims would come a single and entirely different aircraft: relatively high-tech, supersonic, and optimised for ground-attack in a high-threat environment.