Meet the XF-108: The 1950s were a golden age in the aerospace industry. With the development of the jet engine, engineers were constantly testing the boundaries of what this new technology was capable of. The 50s saw a myriad of designs that ultimately never saw the light of day.
One of the most interesting of these projects is undoubtedly the XF-108 Rapier. Designed to be a supersonic interceptor, the XF-108 was built to intercept supersonic nuclear capable bombers. The project was unfortunately canceled in 1959 due to budget and technical constraints as well as the shifting strategic landscape.
XF-108: Origins and Development
The XF-108 Rapier was conceived in the mid-1950s, a period marked by rapid advancements in aviation technology and heightened tensions between the United States and the Soviet Union.
The U.S. Air Force sought a long-range, high-speed interceptor capable of defending the country against supersonic Soviet bombers. Before the advent of ICBMs, nuclear bombers had to fly over their targets directly to drop nuclear ordinances.
As a result, the US and USSR were both engaged in an arms race to develop the fastest nuclear capable bombers. This need led to the development of the Long-Range Interceptor, Experimental (LRI-X) program, which eventually gave rise to the XF-108.
In 1955, the U.S. Air Force issued a specification for an interceptor that could fly at altitudes of 60,000 feet and speeds of Mach 1.7, with a range of 1,000 miles. The aircraft was to have a two-man crew and be equipped with an integrated fire-control system capable of engaging multiple targets during a single mission. North American Aviation, the company behind the legendary P-51 Mustang and the F-86 Sabre, was awarded the contract to develop the XF-108.
Design and Capabilities
The XF-108 Rapier was designed to be a cutting-edge interceptor with impressive speed, range, and altitude capabilities. It was powered by two General Electric YJ93 engines, each producing 29,300 pounds of thrust with afterburners.
These engines were also used in the North American XB-70 Valkyrie, a strategic bomber designed to fly at similar speeds. Although the aircraft was only required to reach Mach 1.7, the designers decided to go a bit further. The XF-108 was expected to reach speeds just shy of Mach 3 (approximately 2,000 mph) and operate at altitudes of up to 80,000 feet.
Despite being designed in the 50s, the XF-108 sported some incredible avionics for its time. The aircraft was equipped with the AN/ASG-18 radar, which had a range of up to 300 miles and could detect bomber-sized targets at about 100 miles. This radar was paired with an infrared search and tracking system, providing the XF-108 with exceptional target acquisition and engagement capabilities. The aircraft was armed with GAR-9 (latter named AIM-47 Falcon) missiles, which had a range of up to 100 miles and were capable of destroying high-speed, high-altitude targets.
The XF-108’s design also emphasized speed and agility. Its sleek, delta-wing configuration and advanced aerodynamics allowed it to achieve high speeds while maintaining stability and maneuverability. Unfortunately, because the aircraft never flew, it remains unknown how maneuverable it actually was in practice. The aircraft’s large fuel capacity provided it with a combat radius of over 1,000 nautical miles, enabling it to intercept enemy bombers far from U.S. shores.
The ICBM Shoots Down the XF-108
Despite its promising design and capabilities, the XF-108 Rapier faced several challenges that ultimately led to its cancellation. One of the primary issues was the high cost of development. The project was estimated to cost around $4 billion (equivalent to approximately $43 billion today), a significant financial burden for the U.S. government.
Additionally, the rapid advancements in missile technology and the shift in Soviet strategy towards ICBMs reduced the perceived need for a high-speed interceptor like the XF-108.
Another challenge was the technical difficulties associated with developing such an advanced aircraft. The XF-108’s engines, radar, and missile systems were all cutting-edge technologies that required extensive testing and refinement. These technical hurdles, combined with budgetary constraints, made it difficult to justify the continued development of the XF-108.
In 1959, the U.S. Air Force decided to cancel the XF-108 Rapier project, just two years after the Soviets launched their first ICBM.
No prototype ever took flight and only a mockup was built. Although the XF-108 never flew, its design and technological advancements influenced future aircraft development, including the F-111 Aardvark and the B-1 Lancer.
The GAR-9 missile would eventually mature into the AIM-54 Phoenix that was paired with the F-14 Tomcat.
Unfortunately, the XF-108 never took to the skies. Its mission to shoot down nuclear bombers was rendered obsolete once the Soviets shifted their strategy in favor of ICBM. Ironically, only five years after the XF-108s cancelation, the Soviets unveiled their supersonic interceptor aircraft, the MiG-25 Foxbat, an aircraft with its own storied history.
Based on the success of the MiG-25 and later MiG-31, one cannot help but imagine an alternate world where the XF-108 went into service and became America’s long serving interceptor.
About the Author:
Isaac Seitz, a 19FortyFive Defense Columnist, graduated from Patrick Henry College’s Strategic Intelligence and National Security program. He has also studied Russian at Middlebury Language Schools and has worked as an intelligence Analyst in the private sector.
