During the early years of the Cold War, America was challenged: how could its bombers penetrate deep into enemy-held territory and fend off faster enemy fighters, long-range missiles, and the threat of nuclear war looming over everything? The answer, one solution put forward, was the “penetration fighter”—an escorting jet to go along with the bombers, sweep the skies clear of menace, and then fly back home.
Lockheed’s response to this issue was the XF-90, designed at the Skunk Works legend by Kelly Johnson and Willis Hawkins.
Taking a lesson from the P-80 Shooting Star, the XF-90 was state-of-the-art in drawings: 35-degree swept wings, Fowler flaps, leading-edge slats, and a swept wings-afterburners-tip tanks combination novel to home production.
Its tail surfaces were adjustable in both directions, another innovative step forward.
But engineering superiority had its price. The XF-90’s airframe was constructed from 75ST aluminum—stronger by far than the more conventional 24ST—but also considerably heavier.
The consequence was an aircraft that would endure incredible forces, such as nuclear shock waves, but whose two Westinghouse J34 turbojets simply could not generate enough power.
Though the plane theoretically achieved 665 mph, with a range of 2,300 miles and a ceiling of 39,000 feet, it fell behind Air Force requirements and its competition.
Flight testing exposed its deficiencies. The XF-90 was able to break the sound barrier only in a dive, and even takeoff needed rocket-assisted boosters.
It was compared unfavorably with competitors such as the McDonnell XF-88 and North American YF-93, as it was slow, clumsy, and underpowered.
When the Air Force chose the XF-88 as its favored aircraft, the penetration fighter idea lost momentum as strategic needs changed and appropriations ended.
But the XF-90 became oddly famous due to its unparalleled durability. One of the prototypes was subjected to stress tests at the National Advisory Committee for Aeronautics, and the second one was shipped to the Nevada Test Site for nuclear weapons tests.
The tests yielded surprising results: a one-kiloton explosion produced minor fractures only, a 33-kiloton explosion crumpled the nose but did not suffer catastrophic structural damage, and even a 19-kiloton explosion that ripped off the tail left the plane mostly intact.
Amazingly, engineers assessed that it would only take 106 hours to return the plane to airworthiness after the initial explosion.
Years later, the radiation-stained pieces of the XF-90 were unearthed, restored, and put on exhibit at the United States Air Force National Museum in Dayton, Ohio—a rare reminder of a jet that withstood three nuclear explosions.
Though it never saw active duty and failed to fulfill its intended mission, the XF-90 influenced future designs like the F-104 Starfighter. Its story demonstrates that even “failed” aircraft can push technological boundaries and that some machines are built tough enough to endure both battlefield stress and atomic fire.