Subterrene

Subterrenes existed first in fiction as mechanical drillers,[citation needed] with real-world thermal designs and examples following in the second half of the 20th century.

Fictional subterrenes are often depicted as cylindrical in shape with conical drill heads at one or both ends, sometimes with some kind of tank-tread for propulsion, and described either as leaving an empty tunnel behind them, or as filling the space behind it with mining debris such as the Thunderbirds Mole.

Tunnel boring machine themselves are not usually considered to be subterrenes, possibly because they lack the secondary attributes – mobility and independence – that are normally applied to vehicles.

A real-world, mobile subterrene must work thermally, using very high temperature and immense pressure to melt and push through rock.

Patents issued in the 1970s[1] indicate that U.S. scientists had planned to use nuclear power to liquefy lithium metal and circulate it to the front of the machine (drill).