Key Points and Summary – Conceived in the 1950s to swat Soviet bombers before they reached U.S. airspace, the North American XF-108 Rapier promised Mach 3 performance via twin GE J93s and a novel internal rotary launcher for three long-range GAR-9 missiles.
-Paired doctrinally with the XB-70 Valkyrie, the Rapier embodied multi-mission ambitions—intercept and potential strike—at extreme speed.
XB-70 Is a Massive Bomber. Image Credit: National Security Journal.
-But heat loads, fuel demands, bay-volume tradeoffs, launcher complexity, and soaring cost collided with shifting realities: the USSR’s pivot from bombers to ICBMs.
-By 1959, only a mockup existed, yet XF-108’s concepts—internal weapon carriage, high-Mach aerothermodynamics—echoed in later programs, from stealth bays to Mach-class reconnaissance.
The XF-108 Rapier Could Have Been a Mach 3 Dominator
It was the 1950s, and President Dwight Eisenhower knew that countering the Soviet Union’s nuclear weapons’ delivery mechanisms created a new era of warfare. One of the concerns with U.S. nuclear doctrine was stopping Soviet bombers from dropping atomic weapons. The Americans needed to deploy an ultra-fast interceptor to protect the country and keep a Russian nuclear strike airplane out of U.S. airspace.
The solution was a jet called the XF-108 Rapier, and it was designed to have a speed of Mach 3, powered by two powerful General Electric J93 engines. A fighter that fast would outmatch any Soviet airplane and could have evaded air defenses.
This Airplane Would Have a Multi-Mission Skill Set
The Rapier could have been an air superiority fighter and even a multi-role airplane for ground strike if missile technology had progressed further. The high speed would have enabled the kind of radar evasion and elusiveness that made for a compelling case to produce it in numbers.
MACH 3 Rapier Fighter With the Equally Fast Valkyrie Bomber
The XF-108 would have been a complementary fighter jet to the XB-70 Valkyrie, a Mach 3 strategic bomber.
XB-70 Bomber from National Security Journal. Taken at USAF Museum in Dayton Ohio on 7/19/2025.
Having a one-two punch with these airplanes was going to be irresistible to American battle planners seeking a high-speed edge to suppress enemy air defenses and protect against enemy strike platforms.
Our friends at the War Zone described how the XF-108 had an innovative and compelling feature that set it apart from other aircraft. The Rapier was to deploy a rotary missile launcher.
This could have been used in ground strikes and for dog-fighting. Imagine the high-velocity flight with a “quick fire” ability to send missiles down range and destroy enemy aircraft or ground targets. This airplane would show Eisenhower that the U.S. Air Force was considering ways to win wars, not just defend the homeland.
XB-70 in Dayton, Ohio Air Force Museum. Image Credit: National Security Journal.
It Took Four Years of Work, and Only a Mockup Was Produced
Construction of the XF-108 began in 1955, and by 1959, a mock-up had been completed.
Could the XF-108 Be Produced in Numbers?
The Mach 3 speed would generate a significant amount of heat, as the engines were mighty.
Pilots would have to be exceptionally skilled and able to concentrate fully during missions. However, the extra effort would have been worth it. Being able to outfly Soviet airplanes of all types would compensate for the difficulties in producing and piloting the warbird.
First, the rotary launcher had to be fastened to the airplane. This was not going to be an easy task. The engineers had a difficult time shaping it to be small enough to be mounted under the fuselage.
“The weapons launcher, which would have carried three of the long-range GAR-9 missiles on a T-shaped assembly, was designed to fit the relatively slim stores bay in the lower fuselage between the XF-108’s huge engines and intakes. As the weapons bay door opened, it rotated to expose the missiles, meaning there were no doors that extended into the airstream,” according to the War Zone.
This was going to be complicated and may have created too much weight. The GAR-9 missiles were huge and took up much room in the fuselage. But the internal storage was an important innovation for future flight in stealthy fighters and bombers that came much later. It was a testament to American ingenuity that the technicians were able to even ponder such a technological advancement.
Was the Rotary Launcher Going to Work?
What would happen when the GAR-9 missiles were launched? Would this have affected the Mach 3 speed of the aircraft and hurt maneuverability? These were potential drawbacks of the rotary launcher. Then, at high speed, the launcher would have to rotate internally. There was much room for error with the contraption.
Each time it fired a missile, it would be exposed. This would have created more drag and an imbalance at a speed of Mach 3. A faulty launch would have been potentially disastrous.
Maximum Amount of Fuel Needed Instead
Another design problem was that Mach 3 required a massive amount of fuel. The internal rotary launcher would have robbed the Rapier of desperately needed fuel capacity. This would have affected the range.
It would have crimped the airplane’s ability to fly all the way to the Soviet Union or Europe. Some trade-offs were necessary then. Either keep the existing, more powerful missiles on the rotary launcher or choose to go with a smaller launcher and less explosive projectiles.
The Air Force wanted it to be able to destroy three enemy airplanes per mission at Mach 3. That was intriguing, especially if each Rapier could shoot down this number of enemy bombers, which could help prevent a Soviet strike.
XF-108 In One Word: Cancelled
As often happens with futuristic experimental airplanes, technology progressed in other systems. Instead of using bombers to deliver nuclear weapons, the Soviets were switching over to nuclear-tipped ballistic missiles.
The XF-108 would not have been capable of identifying, tracking, and destroying ICBMs. The Rapier was a solution searching for a problem by the 1960s. It never progressed beyond the mockup stage.
But what a great concept. The MACH 3 speed was something the Air Force was pondering that could have made a difference in the balance of power. The Americans later developed the MACH 3 SR-71 Blackbird, but this airplane was never armed. The internal rotary launcher was also ahead of its time.
The Air Force demonstrated its ability to develop innovative airplane concepts, which were necessitated by the competition with the Soviets.
Eisenhower had left the White House by the time ICBMs became a significant concern, and it was unclear whether President John F. Kennedy was interested in the latest developments with fighter jets. He was not an aviator while serving in the U.S. Navy.
But the XF-108 helped other programs with design and ambition, and that made it a worthwhile endeavor even though it never progressed beyond a mock-up.
About the Author: Brent M. Eastwood
Brent M. Eastwood, PhD is the author of Don’t Turn Your Back On the World: a Conservative Foreign Policy and Humans, Machines, and Data: Future Trends in Warfare plus two other books. Brent was the founder and CEO of a tech firm that predicted world events using artificial intelligence. He served as a legislative fellow for US Senator Tim Scott and advised the senator on defense and foreign policy issues. He has taught at American University, George Washington University, and George Mason University. Brent is a former US Army Infantry officer. He can be followed on X @BMEastwood.
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