Interceptor ahead of its time

BY ERIK SIMONSEN

During the early 1950s, as strategic planners at North American Aviation were surveying requirements for the next decade, two significant advanced concepts began to emerge.

One was a Mach 3+ intercontinental bomber, later designated the XB-70 Valkyrie, the other a long-range Mach 3+ interceptor that could protect the entire North American continent from intruders carrying nuclear arms.

In November 1955, the U.S. Air Force awarded study contracts to NAA, Lockheed and Northrop after the completion of a Phase I advanced interceptor competition initiated during September of that year.

NAA was awarded the development contract on June 1, 1957, for what was officially known as Weapons System 202A. Designated the F-108, a full-scale mockup was completed and on January 20, 1959, presented to the Air Force. Named Rapier in May 1959, and slightly preceding the development of the XB-70, the Department of Defense and NAA considered the F-108 a significant technological leap.

Ambitious as the project was, NAA felt the development of the advanced interceptor was well within its capabilities. With unmatched mass production credentials, NAA had developed the first operational supersonic fighter, the F-100, and was concurrently developing the Mach 2 A-3J Vigilante (later RA-5C) for the Navy.

As a cost-saving measure while developing the F-108, NAA instituted a program of shared technologies with the proposed XB-70. The interceptor would incorporate the same basic 30,000-pound-thrust YJ-93 engine, honeycomb stainless steel materials and clamshell escape systems as the XB-70. The F-108 also could be utilized as an escort for the B-70.

Operating at Mach 3 at 75,000 feet (and zoom climbing to 100,000 feet), the Rapier would have provided U.S. air defenses an effective look-down-shoot-down capability, intercepting potential adversaries with nuclear arms well away from U.S. borders.

While air defense was considered top priority within some circles, U.S. defense budgets began to flow in favor of intercontinental ballistic missile development.

As a result, NAA's fighter legacy would come to an end on September 23, 1959, with a statement from the Air Force announcing that the F-108 program was being canceled. This decision resulted in a domino effect by immediately negating the shared technology program and dramatically increasing the cost of the embryonic XB-70—a factor leading to its eventual cancellation.

No Rapiers would be built, and its advanced AN/ASG-18 radar system and funding soon would be transferred to the classified Lockheed YF-12A/F-12B. Yet, surprisingly, in 1968 the promised F-12B Mach 3+ interceptor also was canceled, twice leaving the United States without a high-technology air defense fighter.

The U.S. strategy of nuclear intercontinental ballistic missile parity with the Soviet Union was reflected in the eventual selection of the F-106 Delta Dart as the nation's top air defense fighter. Though it was an excellent aircraft, its Mach 2.3 supersonic performance in afterburner was limited to about 12 minutes. The rationale for a Mach 3+ interceptor had been to meet threatening nuclear-armed bombers quickly, keeping any fallout from jettisoned ordnance or premature detonations far from the United States. The F-108 would have intercepted targets a thousand miles from its base.

Fortunately, during the Cold War the Soviet bomber force did not evolve into an overwhelming threat—and the delayed supersonic Tupolev Tu-160 Blackjack achieved limited production.