stage of development, but with no effective launch platform. The AIM-54 Phoenix, developed for the F-111B fleet air defense fighter, had an airframe with four cruciform fins that was a scaled-up version of the AIM-47. One characteristic of the Missileer ancestry was that the radar sent it mid-course corrections, which allowed the fire control system to "loft" the missile up over the target into thinner air where it had better range. The F-111B was canceled in 1968. Its weapons system, the AIM-54 working with the AWG-9 radar, migrated to the new U.S. Navy fighter project, the VFX, which would later become the F-14 Tomcat. The AIM-54 Phoenix was also considered by the Royal Air Force to be used on Avro Vulcan bomber planes as part of an air defence aircraft. This missileer conversion would have used 12 missiles onboard and an extensive modification to the Vulcan's radar. In 1977, development of a significantly improved Phoenix version, the AIM-54C, was developed to better counter projected threats from tactical anti-naval aircraft and cruise missiles, and its final upgrade included a re-programmable memory capability to keep pace with emerging ECM. Usage in comparison to other weapon systems The AIM-54/AWG-9 combination had multiple track capability (up to 24 targets) and launch (up to six Phoenixes can be launched nearly simultaneously); the large missile is equipped with a conventional warhead. On the F-14, four missiles can be carried under the fuselage tunnel attached to special aerodynamic pallets, plus two under glove stations. A full load of six Phoenix missiles and the unique launch rails weighs in at over , about twice the weight of Sparrows, putting it above the allowable bringback load (which also would include enough fuel for go-around attempts). As such, carrying six Phoenix missiles would necessitate the jettison of at least some of the Phoenix missiles if they were not used. The most common air superiority payload was a mix of two Phoenix, four Sparrow, and two Sidewinder missiles. Most other US aircraft relied on the smaller, semi-active medium-range AIM-7 Sparrow. Semi-active guidance meant the aircraft no longer had a search capability while supporting the launched Sparrow, reducing situational awareness. The Tomcat's radar could track up to 24 targets in track-while-scan mode, with the AWG-9 selecting up to six potential targets for the missiles. The pilot or radar intercept officer (RIO) could then launch the Phoenix missiles once parameters were met. The