During the early Cold War years, American military strategists grappled with a novel and disturbing dilemma: how to get America’s bombers to drop their bombs deep within enemy lines—and have them return home—while confronting more speedy fighter planes, extended-range missiles, and the specter of nuclear conflict. One solution, at least in the short term, was the “penetration fighter,” an escort that would fly with bombers into enemy airspace, clean out danger from the route, and battle its way back out.
Lockheed’s contribution to this competition was the XF-90, a slender but cumbersome jet fighter devised at the legendary Skunk Works by Kelly Johnson and Willis Hawkins. Drawing on experience from the P-80 Shooting Star, the XF-90 was designed to be state of the art: it had 35-degree swept wings, Fowler flaps, slats on the leading edge to improve airflow, and the first domestically produced combination of swept wings, afterburners, and tip tanks. Its tail surfaces were adjustable in both directions—another innovation that looked ahead.
But by fixing one issue, Lockheed created another. The XF-90 airframe was constructed out of 75ST aluminum, which was vastly stronger than the contemporary 24ST. The fighter emerged at 12 g’s and even survived nuclear shock waves, though that durability came with weight. Its two Westinghouse J34 turbojets, even boosted with afterburners, just didn’t possess the oomph to counter the weight. On paper, it reached 665 mph, with a range of 2,300 miles and a service ceiling of 39,000 feet—numbers that lagged behind both the Air Force’s requirements and the competition.
In flight testing, the XF-90 did not perform well. It was able to break the sound barrier in a dive, but not during level flight. Its lengthy takeoff roll consistently required rocket-assisted boosters merely to lift off the ground. Compared to the McDonnell XF-88 and North American YF-93, it entered slowly, hungry, and clumsy. When the Air Force selected the XF-88 as an alternative, the penetration fighter project itself then dissipated as defense needs changed and appropriations withered.
But the XF-90’s ruggedness would bring it a bizarre type of fame. The prototype was sent to the National Advisory Committee for Aeronautics for stress testing, where it was pushed beyond the breaking point. The second was taken to the Nevada Test Site to be subjected to something even more outrageous—nuclear blast tests.
The findings were staggering. A one-kiloton explosion caused no more than hairline fractures. A 33-kiloton explosion dented the nose and created visible damage, but not to the fuselage. Even when a 19-kiloton blast tore away the tail and buckled much of the skin, the overall structure remained identifiable. Indeed, following the first blast, engineers reckoned that it would only require 106 hours of labor to have it airborne once again.
Years later, the radiation-drenched fragments were retrieved, washed, and put on exhibit at the National Museum of the United States Air Force in Dayton, Ohio—still marked by three nuclear explosions.
The XF-90 never went on duty and never succeeded in its planned function, but its design helped shape later aircraft, such as the F-104 Starfighter. It is a case study of how a “failed” aircraft can advance the technology boundaries—and how some machinery is constructed robust enough to endure both the battlefields and the blast zone.
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