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.