Mirage IVA 03 - the third pre-production prototype of the standard nuclear bomber - roars away at the Paris Air Salon under the full power of its pair of Snecma Atar 9K turbojet engines in June 1967. The prospective British plan was to re-engine the majestic delta bomber with a pair of Rolls-Royce RB.168-25R Spey turbofans.

Fitted with auxiliary fuel tanks under each wing, Mirage IVA 03 shows its belly to the crowd at Paris in June 1967, revealing the distinctive circular radome for the Thomson-CSF “Radar Panoramique” just aft of the intakes. Behind it is a dummy AN-11 nuclear round, carried semi-recessed within the underside of the fuselage.

The Mirage IV was progressively upgraded throughout its long Armee de I’Air career, changing role from high-altitude nuclear bomber to nuclear-capable low-level penetration strike aircraft and reconnaissance platform. The Mirage IV was finally retired from service in the mid-2000s, the big delta having served for some four decades.

By the time 03 was displayed at the 1967 Paris Air Salon, as seen here, the prospect of the Mirage IV in service with the RAF had passed. The type played a significant part, however, in prompting French withdrawal from Nato’s military structure in 1966, the Mirage IV giving France the ability to create a nuclear deterrent of its own.

The first Mirage IV prototype, 01, was essentially a scaled-up two-seat version of the Mirage III fighter, but smaller than the later production-standard Mirage IVA. The prototype made its first flight on June 17, 1959, reaching Mach 1-9 the following month. Note the original fin; the chord was increased on subsequent prototypes.

The fitting of the Rolls-Royce Spey in place of the original Atar engine, combined with the accommodation of British weapons and systems (based on those of Hawker’s cancelled P.1154 V/STOL fighter), would have required considerable changes including a 2ft (0-6m) fuselage extension and revised air intakes to handle the Spey’s almost 30 per cent increase in mass flow. This stretch would allow the carriage of more fuel, but still not enough to meet the RAF’s 1,000 nautical-mile (1,850km) range requirement.

The Spey Mirage IV, a three-view of which is seen here, was a prospective development of the proposed IVO variant intended as a Canberra replacement for the Royal Australian Air Force. The latter remained unconvinced by the big delta, describing it as an “old-fashioned aircraft that merely flies fast into waiting SAMs”.