During the early Cold War, the United States had a pressing issue: how could its bombers travel safely to faraway enemy targets without evading quicker interceptors, long-range missiles, and the constant danger of nuclear war?
One suggested answer was the “penetration fighter”—a high-speed plane designed to escort bombers, sweep the skies clean of threats, and bring itself home without damage. Lockheed responded with the XF-90, designed in the legendary Skunk Works by Kelly Johnson and Willis Hawkins.
Borrowing from predecessors such as the P-80 Shooting Star, the XF-90 had advanced features for its time: 35-degree swept wings, Fowler flaps, leading-edge slats, and a combination of swept wings and afterburners and tip tanks unique to American production at the time. Even the tail surfaces could deflect in both directions, another touch of sophisticated engineering.
Innovation didn’t come cheap, however. The XF-90 was constructed of 75ST aluminum—much stronger than the standard 24ST—but much heavier as well. Although its airframe could withstand extreme stresses, including the shock of a nuclear explosion, its two Westinghouse J34 turbojets did not have the thrust needed to live up to the potential of the aircraft.
In theory, it might reach 665 mph, travel 2,300 miles, and reach 39,000 feet, but in reality, it failed to live up to Air Force standards and trailed behind competing designs.
Under flight testing, its weaknesses became apparent. The XF-90 could only supersonically in a dive, and takeoff involved rocket-assisted boosters.
It was underpowered, heavy, and clumsy in the air compared to rivals like the McDonnell XF-88 and North American YF-93. When the Air Force selected the XF-88 over it, interest in the penetration fighter diminished, and soon funding evaporated.
Even though it never entered service, the XF-90 earned a singular distinction: incredible longevity. One of the prototypes was pushed to the limit at the National Advisory Committee for Aeronautics, and the other was shipped to Nevada for nuclear burst testing.
The findings were astounding: a one-kiloton explosion created only slight fissures, a 33-kiloton blast buckled the nose but failed catastrophically, and even a 19-kiloton explosion that ripped off the tail did not substantially damage the plane. The engineers estimated it would only take 106 hours to get the plane flight-worthy after the initial explosion.
Years after, the radiation-tinged remains of the XF-90 were retrieved, repaired, and put up for exhibit in the United States Air Force National Museum in Dayton, Ohio. Today, it is a testament not just to speed and engineering but to durability under exceptional circumstances.
Although it never saw combat, the XF-90 left an indelible mark on aviation history. It shaped the design of subsequent planes, such as the F-104 Starfighter, and proved that even prototype planes deemed “failures” can advance technology. The tale of the XF-90 serves as a reminder that some vehicles are engineered not only to fly but to withstand titanic forces that would bring down almost everything else.