Key Point: Russia is resurrecting the demons of our shared Cold War past.

After days of speculation by Western analysts that a deadly accident on August 8 that briefly spiked radiation levels in northwestern Russia was tied to tests of an exotic nuclear-powered “Skyfall” nuclear-powered cruise missile, Russian sources confirmed to the New York Times the explosion of a “small nuclear reactor.”

While there’s a tactical rationale behind Russia’s development of a fast, surface-skimming cruise missile with an unlimited range as a means of bypassing American missile defenses, it strikes many analysts as an inordinately expensive, extremely technically challenging, and—evidently!—downright unsafe.

That’s because the United States has tried it before sixty years earlier—and even with the fast-and-loose safety culture of the Cold War 1960s, the poison-spewing radioactive mega missile it began developing was considered too dangerous to even properly flight test.

This project was most famously described in a 1990 article by Gregg Herken for Air & Space Magazine, which remains well worth the read.

In the late 1950s, the United States had yet to deploy the intercontinental ballistic missiles and submarine-launched ballistic missiles that remain two of three pillars of Washington’s nuclear deterrence today. That meant the drawing board was open for alternative methods to threaten Washington’s adversaries with atomic devastation.

One concept was to use a nuclear ramjet propulsion system to create a rocket that could fly for months thanks to a small nuclear reactor on board. The ramjet functioned by sucking in onrushing air while traveling several times the speed of sound, and warming it with its small reactor. The heated air would expand and get squeezed out exhaust nozzles to result in high-speed propulsion.

The resulting Supersonic Low-Altitude Missile (SLAM) was powered by a small reactor codenamed “Pluto,” to be developed by the Lawrence Livermore National Laboratory in Berkeley, California.

While proto-hippies gathered at the nearby university campus, the scientists at the laboratory, under project director Theodore Merkle, were devising a huge missile designed that would make any caught underneath it “deafened, flattened, and irradiated,” as Herken memorably put it in his article.

The SLAM missile was expected to soar towards its Soviet targets at tree-top level, traveling at three times the speed of sound. The combination of low-altitude (reducing detection range) and Mach 3 speed was thought to make it too fast for interception by fighters or surface-to-air missile. The sonic shock wave produced by the huge missile was believed to be strong enough to kill anyone caught underneath it.

The huge missile, laden with up to twelve thermonuclear bombs, would proceed to race towards one Soviet city after another, visiting Hiroshima-level human tragedies upon each. And once the bombs were exhausted, the nuclear-powered missile would…simply keep on going and going like a murderous Energizer Bunny.

Because installing adequate radioactive shielding on such a small reactor would have proven impossible, the SLAM would have spread in its wake trails of cancer-inducing gamma and neutron radiation and radioactive fission fragments expelled by its exhaust.

Project Pluto scientists even considered weaponizing this property by programming the missile to circle overhead Soviet population centers, though how exposing even more people to slow deaths by radiation poisoning would be useful in an apocalyptic nuclear war that would likely leave both nations in ruin in a few days is hard to fathom.

However, realizing the SLAM concept involved a succession of serious technical challenges. For example, a separate conventional rocket system would be necessary for the missile to reach the supersonic speeds at which its ramjet motor could function. That, in turn, meant the reactor had to be designed to withstand the heat and stress of those powerful booster rockets. In fact, it’s believed precisely that problem may have resulted in the deadly accident in Russia this August.

As a result, the Livermore laboratory devised a 500-megawatt reactor so robust it was nicknamed the “flying crowbar.”

Thus, the missile’s structure would need to withstand the intense heat generated by the reactor, estimated to operate at 2,500 degrees Fahrenheit. Thus, the lab commissioned the Coors Ceramic company in Colorado—yes, the same as the beer-brewers of today—to build heat-resistant ceramic fuel elements.

To test whether the various components Project Pluto could coexist non-explosively, an expensive, eight-square-mile test facility was established codenamed Site 401 at the Jackass flats of Nevada.

A nuclear ramjet named Tory-IIA was tested successfully for a few seconds on May 14, 1961, at low power. After three more years of development, a lighter Tory-IIC ramjet was then tested in 1964, operating at near to full power for five minutes. Over 300 tons of pressurized air were channeled to simulate high-speed flight conditions necessary for the ramjet to operate.

Having established the workability of the nuclear ramjet, Merkle’s team then ran into a serious practical obstacle: where on Earth, literally, could a long-range weapon prone to trailing plumes of radioactive pollution behind it be tested? And what would happen if the supersonic weapon with theoretically nigh-unlimited range “got away”—ie., fell out of control, and potentially irradiated American communities? Some scientists even suggested tying the missile to the ground to deal with the latter problem.

Deploying the weapon operationally presented even worse dilemmas, as the missile would likely overfly U.S. allies on its approach to Russia. Even deploying an operational weapon to a remote Pacific island seemed to entail an inordinate amount of radiation poisoning for the surrounding environment.

By then, the United States was well into deploying ICBMs and SLBM missiles, which presented none of these problems and were at the time virtually unstoppable once launched. By contrast, advances in radar and missile technology seemed bound to make the SLAM less invulnerable than had been previously supposed. Finally, in July 1964, the military pulled the plug on the $260 million program—equivalent to over $2 billion in 2019 dollars.

Fortunately, the Pentagon was able to assess that the SLAM did nothing to alter the Mutually Assured Destruction dynamic of Moscow and Washington’s Cold War standoff, except perhaps by provoking an equally terrifying response. Furthermore, it presented undesirable budgetary burdens and intolerable safety and political risks.

Despite technical advances since the 1960s, those same fundamental considerations likely remain true for Russia’s Skyfall missile today.

As John Krzyzaniak succinctly put it in a piece for the Bulletin of the Atomic Scientists:

“The problems with a nuclear-powered missile are so numerous and obvious that some have questioned whether Putin is being hoodwinked by his scientists, or whether he is bluffing to scare the United States back into arms control agreements. In any case, what was once a terrible new idea is now just a terrible old idea.”

Unfortunately, in a climate of escalating paranoia and nuclear arms competition, Moscow is not merely devising exotic new nuclear weapons, but resurrecting the demons of our shared Cold War past.

Sébastien Roblin writes on the technical, historical and political aspects of international security and conflict for publications including the The National Interest, NBC News, Forbes.com and War is Boring. He holds a Master’s degree from Georgetown University and served with the Peace Corps in China. You can follow his articles on Twitter. This piece was originally featured in September 2019 and is being republished due to reader's interest.