the rear portion would fall away. The unmanned booster could also be used as a weapon, if armed. For Project Gusto, the concept had been simplified and reduced to a single aircraft. Code-named FISH or First Invisible Super Hustler, the aircraft was based on a lifting body design that bears some resemblance to the ASSET spacecraft of a few years later. It differed in having the nose taper down to a flat horizontal line instead of the rounded delta of the ASSET, and the fuselage was not as large at the rear. Two vertical control surfaces were placed on either side of the fuselage at the rear, and a small delta wing covered about the rear third of the aircraft. It was to be powered by two Marquardt RJ-59 ramjets during the cruise phase, providing a cruise speed of Mach 4 at , climbing to as it burned off fuel. To endure the intense heat generated by aerodynamic heating at these speeds, the leading edges of the nose and wings were built of a new "pyroceram" ceramic material, while the rest of the fuselage was made of a honeycomb structure stainless steel similar to the material for the proposed XB-70 Valkyrie. After completing its mission, the aircraft would return to friendly airspace, slow, and then open intakes for two small jet engines for the return flight at subsonic speeds. Lockheed's entry had also changed during the research phase. Their original submission was the Archangel II (A-2), another ramjet-powered design, but one that was ground-launched using large jet engines. The committee did not find either entry particularly interesting, and when the B-58B was cancelled by the Air Force in 1959, the entire FISH concept was put in jeopardy. There was some design work on converting the existing A-model Hustlers as FISH carriers, but the aircraft appeared to have limited capabilities for launching the FISH, and the Air Force was unwilling to part with any of their bombers. The committee asked both companies to return with another round of entries powered by the Pratt & Whitney J58 turbo-ramjet. Kingfish After cancellation of the B-58B in mid-1959, Convair turned to a completely new design, similar to their earlier entry in name only. The new "Kingfish" design had much in common with the Convair F-106 Delta Dart, using a classic delta wing layout like most of Convair's products. It differed in having two of