The major advantages offered by variable-geometry (swing-wing) aircraft are a high supersonic performance with the wings swept back; economical subsonic cruising speed with the wings fully spread; a long operational or ferry range; and relatively short takeoff and landing runs at very high weights. An F-111A first flew on December 21,1964, but was not cleared for service to begin production until October, 1967, mainly due to weight problems (the aircraft weighs 47,175 pounds). The US Navy canceled its plans to use the F-111 on aircraft carriers because of its weight, though their pilots who flew it considered it one of the best airplanes built. Production totaled 563 aircraft; the majority remaining in service with the USAF and RAAF (Royal Australian Air Force), and it is expected that this airplane will continue to be important elements of these air forces for many more years. The F-111C had increased span wings, strengthened landing gear, and TF30-P-3 engines. The F-111F is renowned for its sterling work during the Gulf War. This version of the airplane used two 25,100-lb. thrust Pratt & Whitney TF-30-P-100 augmented turbofans, with a maximum speed at optimum altitude of 1,650 mph (or Mach 2.5); maximum speed at sea level of 915 mph (Mach 1.2); service ceiling more than 59,000 feet; and a range with maximum internal fuel of 2,925 miles. Airplane armament is one 20-mm multi-barreled cannon and one 750-lb. B43 bomb, or two B43 bombs in internal weapons bay; three underwing hardpoints on each outer wing panel, the inner four pivoting to keep stores aligned as wings sweep.