Background The F-111B was part of the 1960s TFX program. The USAF's
Tactical Air Command (TAC) was largely concerned with the
fighter-bomber and
deep strike/interdiction roles; their version of the aircraft would be a follow-on to the
Republic F-105 Thunderchief fighter-bomber. In June 1960, the USAF issued a specification for a long-range interdiction and strike aircraft able to penetrate
Soviet air defenses at very low altitudes and very high speeds to deliver tactical nuclear weapons against crucial targets. Meanwhile, the U.S. Navy sought a long-range, high-endurance interceptor to defend its
aircraft carrier battle groups against long-range
anti-ship missiles launched from
Soviet jet bombers, such as the
Tupolev Tu-16,
Tupolev Tu-22, and
Tupolev Tu-22M, along with submarines. The Navy needed a Fleet Air Defense (FAD) aircraft with a more powerful radar, and longer range missiles than the
F-4 Phantom II to intercept both enemy bombers and missiles.
Tactical Fighter Experimental (TFX) The Air Force and Navy requirements appeared to be different. However, on 14 February 1961, the new U.S. Secretary of Defense,
Robert McNamara, formally directed that the services study the development of a single aircraft that would satisfy both requirements. Early studies indicated the best option was to base the Tactical Fighter Experimental (TFX) on the Air Force requirement and a modified version for the Navy. In June 1961, Secretary McNamara ordered the go ahead on TFX despite Air Force and Navy efforts to keep their programs separate. The USAF and the Navy could only agree on swing-wing, two seat, twin engine design features. The USAF wanted a tandem seat aircraft for low level penetration, while the Navy wanted a shorter, high altitude interceptor with side by side seating. The Navy also wanted a radar dish for long range and a maximum takeoff weight of . So McNamara developed a basic set of requirements for TFX based largely on the Air Force's requirements. He changed to a dish for compatibility and increased the maximum weight to approximately for the Air Force version and for the Navy version. Then on 1 September 1961 he ordered the USAF to develop it.
Design phase The Air Force F-111A and Navy F-111B variants used the same airframe structural components and TF30-P-1 turbofan engines. They featured side by side crew seating in an escape capsule as required by the Navy, versus individual
ejection seats. The F-111B's nose was shorter due to its need to fit on existing carrier elevator decks, and had a longer wingspan to improve on-station endurance time. The Navy version would carry an AN/AWG-9
Pulse-Doppler radar and six AIM-54 Phoenix missiles. The Air Force version would carry the AN/APQ-113 attack radar and the AN/APQ-110 terrain-following radar and air-to-ground ordnance. Lacking experience with carrier-based fighters, General Dynamics teamed with
Grumman for assembly and test of the F-111B aircraft. In addition, Grumman would also build the F-111A's aft fuselage and the landing gear. The first test F-111A was powered by YTF30-P-1 turbofans and used a set of ejection seats, since the escape capsule was not yet available. The first F-111B was also equipped with ejection seats and first flew on 18 May 1965. To address stall issues in certain parts of the flight regime, the F-111's engine inlet design was modified in 1965–66, ending with the "Triple Plow I" and "Triple Plow II" designs. The F-111A achieved a speed of Mach 1.3 in February 1965 with an interim intake design. Excessive weight plagued the F-111B throughout its development. The prototypes were far over the requirement weight. Design efforts reduced airframe weight but were offset by the addition of the escape capsule. The additional weight made the aircraft underpowered. Lift was improved by changes to the wing control surfaces. A higher thrust version of the engine was planned. With the F-111B program in distress, Grumman began studying improvements and alternatives. In 1966, the Navy awarded Grumman a contract to begin studying advanced fighter designs. Grumman narrowed down these designs to its Model 303 design; with this, the F-111B's end appeared near by mid-1967. During March 1968 congressional hearings for the aircraft, Vice Admiral
Thomas F. Connolly, then Deputy Chief of Naval Operations for Air Warfare, responded to a question from Senator
John C. Stennis as to whether a more powerful engine would cure the aircraft's woes, saying, ''"There isn't enough power in all
Christendom to make that airplane what we want!"'' By May 1968 both Armed Services committees of Congress voted not to fund production and in July 1968 the DoD ordered work stopped on F-111B. A total of seven F-111Bs were delivered by February 1969.
Replacement The F-111B's replacement eventually entered service as the Grumman F-14 Tomcat. It was derived from Grumman's initial Model 303 design and reused the
TF30 engines from the F-111B, though the Navy planned on replacing them with an improved engine later. While it was lighter than the F-111B, it was still the largest and heaviest U.S. fighter to takeoff and land from an aircraft carrier. Its size was a consequence of the requirement to carry the large AWG-9 radar and AIM-54 Phoenix missiles, both from the F-111B, while exceeding the F-4's maneuverability. While the F-111B was armed only for the interceptor role, the Tomcat incorporated an internal
M61 Vulcan cannon, provisions for Sidewinder and Sparrow air-to air missiles, and provisions for bombs. Basically, the Navy did not see themselves operating a fleet air defense fighter that was, in all essence, a converted Air Force strike bomber. While the F-111B did not reach service, land-based, non-fighter F-111 variants were in service with the
U.S. Air Force for many years, and with the
Royal Australian Air Force until 2010. ==Design==