It seems as if military leaders in early 20th century Germany and Russia were quite serious about designing a subterranean combat vehicle.
In fact, the German-based Ritter Engineering went so far as to sketch a colossal armored vehicle dubbed the Midgard-Schlange.
Named after a demonic monster which looped the whole earth with its giant length, the hybrid armored vehicle was envisioned as both a tank and tunnel excavator to take on Allied forces during WWII - with some even hoping it could tunnel under the fortifications of the French Maginot Line.
Propelled by 14 engines providing an awesome 19,800 hp, the Midgard-Schlange was also supposed to be capable of traveling underwater.
Unsurprisingly, the project was ultimately shelved, but apparently not forgotten, as Nikita Khrushchev of the Soviet Union expressed interest in designing such a vehicle - albeit with nuclear capabilities.
According to EnglishRussia, the Kremlin ordered its scientists to build a Midgard-Schlange prototype. Soviet leader Leonid Brezhnev eventually axed the "foolish project," but not before the prototype exploded, killing its 5-person crew while attempting to tunnel through a mountain.
Check out some more of the pictures below: