Production ended in 1976 after 563 F-111 aircraft were built. The F-111 was an all-weather attack aircraft, capable of low-level penetration of enemy defenses to deliver ordnance on the target. The F-111 featured variable-geometry wings, an internal weapons bay and a cockpit with side-by-side seating. The cockpit was part of an escape crew capsule. The wing sweep varied between 16 degrees and 72.5 degrees (full forward to full sweep). The wing included leading edge slats and double slotted flaps over its full length. The airframe was made up mostly of aluminium alloys with steel, titanium and other materials used in places. The fuselage was made of a semi-monocoque structure with stiffened panels and honeycomb structure panels for skin. The F-111 used a three-point landing gear arrangement, with a two-wheel nose gear and two single-wheel main landing gear units. The landing gear door for the main gear, which was positioned in the center of the fuselage, also served as a speed brake in flight. Most F-111 variants included a terrain-following radar system connected to the autopilot. The aircraft was powered by two Pratt & Whitney TF30 afterburning turbofan engines. The F-111's variable-geometry wings, escape capsule, terrain following radar and afterburning turbofans were new technologies for production aircraft. The F-111 featured an internal weapons bay that could carry bombs, a removable 20 mm M61 cannon or auxiliary fuel tanks. For bombs, the bay could hold two 750 lb (340 kg) M117 conventional bombs, one nuclear bomb or practice bombs. The F-111B for the US Navy was to carry two AIM-54 Phoenix long-range air-to-air missiles in the bay. The cannon had a large 2,084-round ammunition tank, and its muzzle was covered by a fairing; however, it was rarely fitted on F-111s. The F-111C and F-111F were equipped to carry the AN/AVQ-26 Pave Tack targeting system on a rotating carriage that kept the pod protected within the weapons bay when not in use. Pave Tack featured a forward looking infrared (FLIR) sensor, optical camera and laser rangefinder/designator. The Pave Tack pod allowed the F-111 to designate targets and drop laser-guided bombs on them. Australian RF-111Cs carried a pallet of sensors and cameras for aerial reconnaissance use.