Seeking the Soviet Battle Mole

by Brian Dunning
August 16, 2022

The year was 1964, the place was the Ural Mountains in the Soviet Union. Under leaden skies, the crew of five climbed aboard the gigantic vehicle, which looked something like a dark metal cigar, 35 meters long and 3 meters in diameter. Its nuclear reactor, borrowed from the newest class of Soviet nuclear submarines, hummed to life. Soon the mighty machine leapt forward and appeared to collide catastrophically with the face of a mountain, but instead, it seemed to melt right into the rock, using the nuclear reaction's extreme heat to literally melt its path into the mountain. It disappeared into the solid surface like a snake into its burrow. The team of engineers and military officers on hand ran over and stared into the gaping hole, its sides of hot glass glowing orange. The rear end of the mechanical marvel could just be seen disappearing into the dark as the glass hissed and steamed and cooled. The first test of the Soviet's so-called "underground boat" had been a success. At least, it was according to the story.

The star of their "underground boat" program was the vehicle they nicknamed the Battle Mole, and which the Americans termed a subterrene, descended from the latin for underground. Whether it ever existed is a big question, given that there's basically one single apocryphal story — found reproduced in books and on mostly Russian-language websites — comprising the entirety of the evidence for it. We'll have a more detailed look at that story in a moment.

But first, we should be clear on what we're talking about here. Most everyone is familiar with the Tunnel Boring Machine (TBM) used around the world for applications such as subterranean roadways, and first developed during the 1800s. These are great big machines, assembled in place, with a great big cutter head with dozens of disc cutters to break away the rock, then transport the debris backward along conveyor belts and into carts or trucks for removal. Some simultaneously install concrete support plates as they inch forward. The entire machine is on hydraulic legs and jacks that both move it along and keep forward pressure on the cutting head.

Conversely, a subterrene — in concept, anyway — is a self-contained vehicle with independent mobility. Its crew can jump in, drive around underground wherever they want, jump out and do it again tomorrow. It's a real autonomous vehicle, not a great clunky machine that has to be assembled and disassembled at job sites.

How independently mobile was the Battle Mole? Following the success of the first test already described, a subsequent test was contrived. This time, the vehicle managed to travel 10 kilometers, at what was described as great speed, through all different types of geology: solid rock, broken rock, sand and gravel; melting each into a solid and incredibly strong tunnel wall, leaving no debris behind it. But then, disaster struck. The accounts say that the vehicle exploded in a thermonuclear fireball, deep underground, vaporizing its commander, Colonel Semyon Budnikov, and the rest of his crew. The tunnel was thoroughly collapsed by the catastrophe, so no attempt was ever made to find the vehicle's remains, and the program was effectively terminated at that point.

Now obviously there are some implausibilities to this account, at least the way it's told. If a fission reactor such as that from a submarine could be designed to generate sufficient heat to melt rock with extreme speed, there would have been no way to cool the machine or its occupants as it was encased within a molten-walled tunnel with nowhere to disperse waste heat. It's physically impossible for the material melted from the tunnel to simply vanish and not fill the tunnel behind the vehicle. And of course the big one: although a fission reactor can certainly melt down, it has no mechanism to generate any explosion other than a steam explosion. Fission reactors have nothing in common with a device capable of triggering a thermonuclear explosion.

However, this is not a case where we just wave our hand and dismiss the story as simply made-up science fiction. We can be absolutely assured that the Soviet nuclear subterrene was, at the very least, an absolutely serious concept. How? Because we know that it was an absolutely serious concept at the United States' national laboratories during the cold war. There are literally hundreds of published papers available at the US Department of Energy's Office of Scientific and Technical Information, most of them created at Los Alamos in the 1970s.

One design is for a small coring device called a "geoprospector", a hollow tube a mere 300mm (1 foot) wide. Made of either molybdenum or tungsten to withstand the 2000K heat of its 100 kW electric heating elements at its leading edge, it would melt its way into the rock at half a millimeter per second and extrude a glass-encased sample core at its aft end. A number of small scale subterrenes of this basic design were built and successfully tested.

Another design, dubbed the SUBSELENE, was intended for use on the Moon to create tunnels shielded from radiation for human habitation and transportation. Like the geoprospector it was an uncrewed machine, but like the Battle Mole, it was powered by an onboard nuclear reactor. Five meters in diameter, its 134 individual melting elements would be heated by liquid metal circulating from the onboard 400 MW reactor. Its design speed was to tunnel 80 meters per day. The melted rock would be used in two ways, to create a solid glass lining for the tunnel, and to create other "useful forms" such as building materials, which would be extruded out the back of the machine as it goes.

The largest design concept was a six meter machine that would have been something of a cross between a subterrene and a TBM. Nuclear powered, this one melted and cut using the kerf technique, meaning only the outer edge of the circular cutting head used heat from the reactor to melt the rock. This melt was used to form the glass lining. The rest of the rock was removed by conventional mechanical cutters, similar to a TBM, and the material was crushed into a slurry and piped out the back.

There are other reports covering the use of rock melting for creation of storage tunnels for nuclear waste, for accessing geothermal energy, for lining boreholes with glass far less expensively than conventional lining, for running underground power transmission lines, and other applications. But nowhere in any of these hundreds of documents produced by the Los Alamos Subterrene Program was there a single design concept for a crewed vehicle, or a weaponized subterrene of any sort, or of anything that was magically free of the problem of debris removal, or of anything that moved freely through the rock at speeds useful for transportation or battle.

So here's what we have. First, solid proof that subterrenes were being taken seriously by the United States during the cold war, which makes it a safe bet that their Soviet counterparts were doing the same; second, we have an urban legend about a successful Soviet subterrene that blew up. Urban legends aren't proof of anything, especially ones that are full of so many implausible elements. So we are faced with a perfectly plausible question: Were the Soviet Battle Moles ever actually real?

Even the Russian language literature is very thin with information about the Soviet subterrenes. Those that are discussed bear little resemblance to the American designs. They were enormous mega-machines more like underground tanks than scientific instruments. They rode on mighty tank tracks and the concept drawings show giant conical drillheads at the front, like something from a Jules Verne novel. There's no mention of them using reactor heat to melt the rock, only conventional cutter heads.

The earliest Soviet design was from the 1930s, the product of the engineer Alexandr Trebelev, and is where the term "underground boat" came from. Driven by a single operator, the boat was powered by electrical cables pulled behind it. Its application was to go deep, drive around until it found an oil deposit, pulling a pipeline behind it all the way. Trebelev's prototype never made it more than twelve meters before breaking down, and the project was abandoned.

After World War II, Nikita Khrushchev took a keen interest in developing exotic systems. The Soviets had captured German plans for a subterrene called the Sea Lion that was never built, intended to take a crew of 5 under the English Channel, tunnel right underneath any target they chose, and plant a giant bomb. It was completely impractical, but with the advent of nuclear reactors in the 1960s, Khrushchev took another look at it. The idea would be to tunnel up to American underground missile facilities and command posts without being detected, and blow them up. This was to be the Battle Mole. It had a crew of five, fifteen armed troops, and one ton of explosives. It used a conventional cutter head powered by electricity from the reactor. It moved at 7 kph, a fast walking speed. The tests, culminating with the disastrous one already discussed, are said to have taken place in 1964.

The accounts all end with Leonid Brezhnev coming to power shortly after the loss of the Battle Mole, and the termination of the program, destruction of all materials, and the entire thing was classified. It's a little too convenient of a way to end the story, as the lack of evidence moves the entire thing into the realm of faith.

And faith is where the entirety of the Battle Mole story remains. While Trebelev's earlier unsuccessful machine is documented and known to have been real, no evidence has ever surfaced that the Battle Mole was ever built. We already know that even today's best TBMs cannot come anywhere remotely close to 7 kph, and any preliminary testing done by the Soviets would have taught them the same thing. The American nuclear subterrene designs didn't come anywhere close to that speed either. Nothing about the Battle Mole was practical. Its original iteration in Russian language pulps gave it a conventional mechanical cutter head, and its later American-style heating element to melt into the rock only appears in a few modern Internet articles written after the Los Alamos Subterrene Program could inspire imaginative authors. Given that storytellers have been free to take liberties of that magnitude with it, and given that the story ends with an assurance that no evidence will ever be forthcoming, we can rest assured that it probably never existed.

A final note is the Battle Mole's total lack of similarity to the American designs from Los Alamos. Realistically, we would expect Soviet intelligence to have learned about the subterrenes, and we'd also expect them to attempt something similar. Whatever testing the Americans did, it's obvious that nobody cuts tunnels like this today. We don't know why the melting technique didn't catch on, probably its problems didn't justify any efficiencies it may have had. So it's probable that the Soviets, assuming they did follow the American work, came to the same conclusion. If they did, the 1970s were long after the Battle Mole's alleged 1964 misadventure, so it's yet another reason the entire story just doesn't hold up to scrutiny. Enjoy a good piece of Jules Verne style fiction for what it is; but don't mistake it for historical fact.

By Brian Dunning
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