questioned the Mirage IV*'s capacity to operate from unprepared airstrips or to operate at low level, or claimed that the F-111 was a superior aircraft "in a class of its own". Air historian Bill Gunston notes that low-level Mirage IV missions had been planned since 1963 and Mirage IVs operated regularly at low level since 1965, and argues that the ability of a strategic bomber to operate from unprepared airstrips is historically unimportant. Ultimately, as much for strategic political reasons as for technical ones, the F-111K was preferred (only to be cancelled later in its turn) and the Spey-engined Mirage abandoned. BAC and Dassault had also hoped to sell the Mirage IV* to France and to export the Mirage IV* to various nations, such as India, possibly Israel, and others; the lack of a British sale put an end to such possibilities. Some aviation journalists claim that the rejection of the Mirage IV* may have dampened French interest in joint Anglo-French cooperation. Design The Mirage IV shares design features and a visual resemblance to the Mirage III fighter, featuring a tailless delta wing and a single square-topped vertical fin. However, the wing is significantly thinner to allow better high-speed performance and has a thickness/chord ratio of only 3.8% at the root and 3.2% at the tip; this wing was the thinnest built in Europe at that time and one of the thinnest in the world. While being significantly smaller than an expensive medium bomber proposal for the role, the Mirage IV was roughly three times the weight of the preceding Mirage III. The Mirage IV is powered by two Snecma Atar turbojets, fed by two air intakes on either side of the fuselage that had intake half-cone shock diffusers, known as souris ("mice"), which were moved forward as speed increased to trim the inlet for the shock wave angle. It can reach high supersonic speeds: the aircraft is redlined at Mach 2.2 at altitude because of airframe temperature restrictions, although it is capable of higher speeds. While broadly similar to the model used on the Mirage III, the Atar engine had a greater airflow and an elevated overspeed limit from 8,400 rpm to 8,700 rpm for greater thrust during high altitude supersonic flight. While the first Mirage IV prototype was fitted with double-eyelid engine nozzles, production aircraft featured a complicated variable geometry nozzle that automatically varied in response to the