The British TSR.2 and American F-111 (nicknamed "Arrdvark", or "Vark") both were strike aircraft developed in the late 1950s through the 1960s. Both were intended to be low-level interdiction aircraft with top speeds of over Mach 2, capable of both long-range strike and reconnaissance missions. Both had troubled development, and only one made it into service.
The TSR.2s engines had been problematic at the start. For its first flight, the engines were limited to 97 percent thrust any more, and a catastrophic failure would have been likely. For all intents and purposes, the TSR.2 would have been underpowered until the engines were fixed. That happened, but the engines were not as big a problem as the range. Even then, the engines produced big plumes of smoke. Combined with the contrails it made acquiring a TSR.2 visually a relatively easy task. It was fast, though, and the upgraded Olympus turbojet designed for the TSR.2 was later the basis of the engines used in the Concorde supersonic transport.
The TSR.2 was supposed to have a combat radius of 1850 kilometers. It could achieve that radius with only a 2,000-pound bombload. Thats not much in essence, it could deliver a nuclear weapon or carry out reconnaissance missions. But if a TSR.2 carried its maximum bombload (10,000 pounds), it was limited to a 741 kilometer combat radius. Compare this to the F-111s combat radius of 2,140km carrying a bombload of 30,000 pounds. This was due to the decision to use the TF-30, a turbofan, which was much more fuel-efficient than the turbojets used on the TSR.2. The F-111 only needed 5043 gallons of internal fuel compared to 6,716.6 gallons on the TSR.2 to attain the combat radius it did. Australia backed out of buying the TSR.2 and went instead with the F-111, which is projected to remain in Australian service until 2015. Ultimately, facing rising costs, the TSR.2 was cancelled in favor of the F-111 in 1965.
The F-111 had its engine problems, too. The TF-30 was known to stall in certain circumstances, and the first combat deployment of the F-111A in 1967 was a near-disaster, with three planes lost out of eight sent in 1967. The F-111s problems led to the UK canceling that purchase in 1968. It was a bad decision, because by 1972, the F-111 had become a deadly strike aircraft that flew 4,000 missions over Vietnam with only six aircraft lost in action, while operating without tanker or ECM support. It went on to serve for another 25 years and in Operations Desert Storm and Eldorado Canyon, retiring in 1997. Harold C. Hutchison (email@example.com)