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It was a weapon so horrifying, so apocalyptic, that even the men who designed it weren’t sure if it should exist. Imagine a missile that never needed to land, never needed to refuel, and could roam the skies for weeks—dropping nuclear bombs one after another while leaving a radioactive trail of destruction in its wake. This was Project Pluto, the most terrifying weapon the Cold War almost unleashed.
At the height of U.S.-Soviet tensions in the 1950s, nuclear deterrence was everything. Both superpowers sought new ways to deliver nuclear weapons, and traditional bombers and missiles had their weaknesses. Bombers could be shot down. Ballistic missiles were fast but followed predictable paths. The answer, the U.S. thought, was something entirely different: a nuclear-powered cruise missile that could stay airborne for weeks, if not months, waiting for the order to rain down destruction.
The concept was as insane as it was ambitious. Engineers at the Lawrence Livermore National Laboratory devised a nuclear-powered ramjet engine called SLAM—Supersonic Low-Altitude Missile. Unlike conventional jets, which burn fuel, SLAM would use a small nuclear reactor to superheat incoming air, creating nearly unlimited propulsion. This meant the missile could fly at Mach 3, skimming just above treetops, evading radar, and weaving through valleys at terrifying speeds.
But that was only part of what made Project Pluto a true doomsday weapon. The missile was designed to carry 16 to 20 nuclear warheads, each capable of obliterating a city. It would enter enemy territory at low altitude, releasing one warhead at a time before moving on to the next target. Once it had dropped all its bombs, it wouldn’t simply crash—it would continue flying, spewing deadly radiation from its unshielded nuclear reactor, turning the very air behind it into a toxic wasteland.
The mere presence of such a weapon in the sky would create chaos. Its supersonic shockwave alone could knock down buildings, and its radioactive exhaust would poison anything in its path. Theoretically, it could stay airborne indefinitely, circling like a vulture over enemy territory, waiting for the perfect moment to strike. It wasn’t just a missile—it was a flying nuclear nightmare.
Despite its terrifying potential, Project Pluto was ultimately too dangerous for even the U.S. military. Testing the engine alone was a challenge—how do you safely fire up a nuclear-powered jet without irradiating everything around it? While ground tests of the reactor were successful, the idea of launching an unshielded nuclear reactor into the sky, where it could crash or spiral out of control, raised serious concerns.
By the early 1960s, intercontinental ballistic missiles (ICBMs) had become the preferred method of nuclear delivery. They were faster, harder to intercept, and didn’t come with the same uncontrollable risks as a flying nuclear reactor. In 1964, Project Pluto was quietly canceled.
The world never got to see this apocalyptic machine in action—but just knowing it existed, even on paper, is enough to send shivers down the spine. Project Pluto was the ultimate doomsday device, a weapon so terrifying that even the superpower that built it decided it was too much.