In the 1950s, the Jet Age was in full stride, with manufacturers working to achieve groundbreaking advancements using this new technology. While high-performance internal combustion engines had dominated the 1940s, the jet engine—initially developed at a slower pace—quickly revolutionized the aircraft industry once its potential became obvious to engineers. This thriving post-war period is often regarded as the golden age of aircraft design, as no idea seemed too bold or unconventional.
During this era, the United States produced a fascinating variety of experimental aircraft that embraced this new technology, including the XF-84 “Thunderscreech,” the Lockheed XFV, and the VZ-9 Avrocar.
Among the more radical aircraft proposed during this time was the XF-108 Rapier.
The XF-108: an interceptor for the ages
The aircraft was developed by North American Aviation, the same company responsible for creating the iconic P-51 Mustang. Had the XF-108 ever taken flight, it would have stood as one of the most advanced and highest performing aircraft of its time.
Its creation came from the need to defend the United States against the looming threat of Soviet bombers armed with nuclear weapons, should a conflict between the U.S. and U.S.S.R. ever arise. As an interceptor, the XF-108 was engineered for exceptional range and extreme speed, enabling it to intercept and take out Soviet bombers well before they could reach U.S. airspace.
The initial vision for the XF-108 included accompanying the XB-70 Valkyrie bomber, another cutting-edge aircraft under development by North American Aviation. The XB-70 was considered too fast to intercept on its own, but pairing it with a swift, agile fighter like the XF-108 would have further enhanced its survivability during missions.
Unfortunately, the technological challenges faced by designers proved too difficult with the resources available at the time, leading to the abandonment of this ambitious concept. Nevertheless, North American planned to equip both aircraft with the General Electric YJ93 engine to streamline production and reduce development expenses.
The XF-108’s cutting-edge design
Speed was the name of the game for the XF-108. It was powered by two of the aforementioned General Electric YJ93 engines that produced 29,300 pounds of thrust each, with afterburners. This is more than the F-15 Eagle or Eurofighter Typhoon. With this power, the XF-108 was expected to reach a cruising speed just shy of 2,000 mph.
To detect approaching bombers, the XF-108 was equipped with AN/ASG-18 prototype radar. It was paired with an infrared search and tracking system and was highly advanced for the time. This device had a range of up to 300 miles and could accurately detect bomber-sized targets at about 100 miles.
The drawback to the radar was its size, as it weighed nearly 1,000 kilograms.
For shooting down bombers, the XF-108 was armed with three GAR-9 missiles. These were designed alongside the AN/ASG-18 radar and had a range of about 100 miles at a speed of over 3,000 mph. The range of this missile was so great that it had its own radar-guidance system installed so it could still reach its target while out of range of the aircraft it was launched from. They were stored in an internal bay on a rotary launcher.
The interceptor was incredibly large relative to other aircraft at the time. At 27 meters long, the XF-108 was longer than the F-22 Raptor and even a B-17 Flying Fortress.
The XF-108 was shaping up to be a truly deadly aircraft, and one of the most advanced of the era. However, it never got to fly, as it was one of the many victims of the intercontinental ballistic missile.
Cancelation
Both the U.S. and Soviet Union had been hard at work developing intercontinental ballistic missiles (ICBMs) since WWII, having been heavily inspired by Germany’s V-2 rocket. ICBMs were much better at delivering a nuclear weapon than bombers because they were easier to hide, able to reach their target within 30–40 minutes, and able to reach such high speed (around 4 miles per second) that interception would be impossible.
The Soviets achieved the first successful ICBM launch in August 1957 with the R-7 missile. This moment immediately changed the priorities of nations around the world. The ICBM simply rendered the bomber obsolete, and therefore an interceptor to shoot down the bombers was no longer needed.
The XF-108 program was canceled just two years after the launch of the R-7. Only a mock-up had been built.
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The development of the XF-108 wasn’t completely wasted, though. North American Aviation managed to use much of what they had learned from the XF-108 in the A-5 Vigilante, a carrier-based bomber that has a clear lineage to the XF-108.
The AN/ASG-18 radar would later be used in the YF-12 program, and the GAR-9 missile would eventually mature into the AIM-54 Phoenix that was paired with the F-14 Tomcat.