being a factor. With the Mirage IVB considered to be too expensive, the medium-sized Mirage IVA, slightly larger than the first prototype, was chosen for three more prototypes to be produced. This aircraft had a wing area of and weighed about On 4 April 1960, a formal order for 50 production Mirage IVA aircraft was issued. The three prototype aircraft were built between 1961 and 1963, with first flights on 12 October 1961, 1 June 1962, and 23 January 1963. By 1962, the second prototype had conducted simulated nuclear bombing runs in the trials range at Colomb-Bechar in southern Algeria. The third prototype was equipped with the navigation/bombing systems and flight refuelling probe. The fourth prototype Mirage IVA-04 was essentially representative of the production aircraft that would follow. For production, various portions of the aircraft were subcontracted to Sud Aviation (wings and rear fuselage) and Breguet Aviation (tailfin), which was still a separate company from Dassault until 1967; Dassault manufactured the front fuselage and flight-control system internally. Manufacture of both the prototypes and subsequent production aircraft was often hindered by an explicit requirement that there would be no reliance upon foreign suppliers to maintain France's nuclear capabilities; due to this, the Mirage IV initially lacked an inertial navigation system as French industry could not yet produce this device. On 7 December 1963, the first production Mirage IVA performed its maiden flight. A series of 62 aircraft was built, and they entered service between 1964 and 1968. Although Dassault had designed the Mirage IV for the low-level flight role right from the start, the final batch of 12 aircraft ordered in November 1964 differed from the earlier aircraft in several areas, including the flight controls, avionics, and structural details, for the purpose of providing improved low-level performance. It had been planned for this batch to be powered by the newer Pratt & Whitney/SNECMA TF106 turbofan engine. The improvements featured upon the last 12 Mirage IVs were later retroactively applied to the whole fleet. In December 1963 Dassault proposed a Mirage IV-106 variant with 2 Snecma TF106 (license-built Pratt and Whitney) engines, an enlarged 105,000 gross-weight fuselage, terrain-avoidance radar, and armed with a proposed French version of the American Douglas GAM-87 Skybolt air-launched ballistic missile. This version would have been very costly, and ultimately was not ordered. Proposed export variants In 1963, the Australian government sought a replacement for the Royal Australian