Last week, Vladimir Putin's government cryptically announced that there had been an explosion at a missile test center in remote northern Russia that involved the release of radioactive materials. Initially, two people were said to have been killed; the death toll was subsequently raised to seven. A nearby village was ordered evacuated, then the villagers were told to stay put.

U.S. analysts think the accident involved the prototype of a nuclear-powered cruise missile that the Russians call Burevestnik, or Petrel, but is known in the West by its NATO designation, Skyfall. Putin has called it "a fundamentally new type of weapon" - an "invincible missile" with virtually unlimited range, easily able to evade U.S. defenses. When Skyfall was first announced, early last year, some Western military analysts started hyperventilating. "That's a technological breakthrough and a gigantic achievement," claimed one. "These weapons are definitely new, absolutely new."

But in fact, these "new" missiles are a throwback to the early days of the Cold War. And back then, it was the United States that developed a nuclear-powered cruise missile, in the early 1960s. "Project Pluto" was part of a Pentagon program known as Supersonic Low Altitude Missile, a clunky name almost certainly designed to yield its catchier acronym, SLAM. The missile was canceled in 1964, never having taken flight. Nuclear-powered cruise missiles were not a good idea then, and they are not a good idea now.

That's not to say that such weapons are not impressive, in a way. SLAM envisioned a locomotive-sized missile flying at three times the speed of sound near treetop level, tossing out hydrogen bombs along the way and spewing radiation in its wake. In 1990, when I worked at the National Air and Space Museum, I researched the history of the project for an article in Air and Space magazine. There was a reason Pluto's inventors, at the Livermore nuclear weapons laboratory in California, dubbed it "the weapon from Hell." The noise level on the ground when Pluto went by was expected to be 150 decibels. The Saturn V moon rocket, by comparison, produced 200 decibels at full thrust. 

But ruptured eardrums would have been the least of your worries if you were in the neighborhood. The shock wave alone might have been lethal. And since Pluto's nuclear ramjet engine ran at 2,500 degrees Fahrenheit, portions of the missile would have been red-hot - literally "frying chickens in the barnyard" on the way to its targets. Indeed, SLAM operated on the same principle as the errant low-flying B-52 bomber in "Dr. Strangelove." As Maj. Kong observed to his crew, "they might harpoon us, but they dang sure ain't going to spot us on no radar screen." One Livermore engineer told me that SLAM would be deafening, flattening, broiling and irradiating Russians even before it dropped the first bomb on targets in the Soviet Union.

Which was, in part, the problem: Where do you test a flying nuclear reactor? Livermore physicists initially proposed that Pluto be flown in a figure-eight pattern over the remote Pacific, prompting one to ask: "How are you going to convince people that it is not going to get away and run at low level through Las Vegas - or even Los Angeles?" An alternate idea was to tie Pluto to a tether at the Nevada Test Site. ("That would have been some tether," dryly observed another scientist at the lab.) Finally, what do you do with a highly radioactive missile once it's been tested? Dumping it in the ocean was the solution offered back then. And it is probably Putin's preferred solution now.

Ultimately, in the United States, cooler heads prevailed. Six weeks after the successful static test of Livermore's nuclear engine in Nevada in July 1964, the Pentagon pulled the plug on Pluto. Intercontinental-range ballistic missiles promised to destroy targets in the Soviet Union well before Pluto got to them, with equal certainty and a lot fewer associated risks. SLAM, its critics said, stood for "slow, low and messy."

But Pluto, it seems, has risen again, this time in a Russian incarnation - a nuclear-powered Frankenstein, a flying Chernobyl. Putin's Skyfall cruise missile also has a seagoing sibling: a giant nuclear-powered torpedo, dubbed Poseidon, designed to destroy U.S. port cities with a multi-megaton blast. Poseidon bears a striking resemblance to the idea that Russia's Nobel Prize-winning physicist, Andrei Sakharov, came up with in the early 1960s. When Sakharov told a Soviet admiral of his proposal, however, the latter was "shocked and disgusted by the idea of merciless mass slaughter." Feeling "utterly abashed," the physicist abandoned the concept and never raised it again. "I'm no longer worried that someone may pick up on the idea," Sakharov wrote in his memoirs, published in 1990. "It doesn't fit in with current military doctrines, and it would be foolish to spend the extravagant sums required."

Plainly, times have changed. Yet as several experts have since noted, it is also possible that Putin's amazing new weapons are only part of a propaganda campaign, a response to plans announced by the Trump administration to expand and modernize America's nuclear arsenal. If so, Putin's ploy is reminiscent of Soviet Premier Nikita Khrushchev's hollow Cold War boast that the U.S.S.R. was turning out ICBMs "like sausages."  

Of course, flying nuclear reactors and giant nuclear-armed undersea drones could do a lot of damage to U.S. cities if they really existed and were ever used. But the real danger of Putin's Potemkin arsenal is that it will - as Khrushchev's boast did decades ago - spark a U.S. overreaction and lead to pressure to revive ideas like Livermore's Pluto and Sakharov's Poseidon: forgotten relics of Cold War 1.0 that are best left dead and buried.

Gregg Herken is an emeritus professor of American diplomatic history at the University of California. From 1988 to 2003, he was the curator of military space at the Smithsonian’s National Air and Space Museum in Washington, D.C.

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