It was retired to the United States Air Force Museum at Wright-Patterson Air Force Base in 1989. The remaining unconverted F-111As were mothballed at Aerospace Maintenance and Regeneration Center at Davis-Monthan Air Force Base in June 1991. The F-111B was to be a fleet air defense (FAD) fighter for the U.S. Navy, fulfilling a naval requirement for a carrier-based fighter aircraft capable of carrying heavy, long-range missiles to defend aircraft carriers and their battle groups from Soviet bombers and fighter-bombers equipped with anti-ship missiles. General Dynamics, lacking experience with carrier-based aircraft, partnered with Grumman for this version. The F-111B suffered development problems and Navy requirements changed to an aircraft with maneuverability for dogfighting. The swing-wing configuration, TF-30 engines, AIM-54 Phoenix air-to-air missiles and AWG-9 radar developed for this aircraft were used on its replacement, the Grumman F-14 Tomcat. The Tomcat would be large enough to carry the AWG-9 and Phoenix weapons system while exceeding both the F-111's and the F-4's maneuverability. Seven aircraft were completed for testing but the model never entered fleet service. The F-111C is the export version for Australia, combining the F-111A with longer F-111B wings and strengthened FB-111A landing gear. Australia ordered 24 F-111s and, following delays, the Royal Australian Air Force accepted the aircraft in 1973. Four of these were converted to the RF-111C reconnaissance variant in 1979–80. Australia also purchased four ex-USAF F-111As and converted them to C standard. In the 1990s, F-111C aircraft underwent a comprehensive digital avionics upgrade (known as the AUP) which introduced new nav/attack systems (PAVE TACK Laser /infrared targeting system) and flight control computers. The RAAF retired its last F-111Cs in December 2010. The F-111D was an upgraded F-111A equipped with newer Mark II avionics, more powerful engines, improved intake geometry, and an early glass cockpit. The variant was first ordered in 1967 and delivered from 1970–73. The F-111D reached initial operational capability in 1972. Deliveries were delayed due to avionics issues. 96 F-111Ds were built. The sole operator of this variant was the 27th TFW stationed at Cannon AFB, New Mexico.