The B-58A began replacing the B-47s of SAC’s 43rd Bomb Wing at Carswell AFB in March 1960, and the 305th Bomb Wing in May 1961 -the only two wings to get the type. Considering the B-58’s high performance and sophisticated equipment, it was surprising that its service life was curtailed. By January 16, 1970, the last Hustlers were retired from SAC. One reason was the B-58A’s high accident rate, resulting in the loss of nine of the first 30 aircraft, another the growing threat of surface and air launched missiles. And unlike the B-52, it could not be configured for a mass of conventional bombs or missiles.
Delivery of nuclear weapons was limited by the B-58’s short range, and a less expensive and more deadly launcher was the intercontinental ballistic missile (ICBM), whose entrance into SAC paralleled B-58 service. The first SAC Atlas ICBM squadron was declared operational September 2, 1960, and by 1969 enough more advanced ICBMs were on hand for an operational force stabilized at 1,000 Minuteman and 54 Titan missiles, while the Navy had 656 submarine-launched missiles.
Other Bomber Designations
The B-66 tactical bomber has already been described in an earlier section of this chapter. The Radioplane Crossbow (GAM-67) decoy missile used the B-67 designation briefly, and the XB-68 was Martin’s last jet-bomber design. RB-69A was the designation allotted to seven Lockheed P2V-7U Neptunes ordered from the Navy in May 1954 for special electronics intelligence missions.
Martin’s Model 316 was ordered in September 1956 as the XB-68 two-place tactical bomber powered by two Pratt & Whitney 27,500-pound thrust J75s mounted on each side on the long fuselage. Like the company’s earlier XB-51, it had a high T-tail and rotary bomb door, but the 53-foot span wings were straight and short like those on an F-104. Armament included a radar-aimed 20-mm T-171, like the one on the B-58, and a 3,500-pound TX-11 nuclear bomb that was to be carried over a 688-mile combat radius. Estimated top speed was 1,589 mph at 54,700 feet, a velocity requiring evaporation cooling and a steel primary structure.
Although two prototypes and a static-test article had been planned, the XB-68 was canceled early in 1957 to save money, leaving the XB-70 as the only manned strategic-bomber prototype under way. Subsequent numbers were assigned to the SR-71 reconnaissance design and to several missile projects, but the XB-70 would be the last bomber in the series that began with a Keystone biplane in 1927.