The Empire does have some Drill Tanks (or subterrenes, rather – technical term), giant plasma-belching nuclear-powered monsters which carve their way through rock, cleaning up the waste as they go and leaving steaming glass-lined tunnels behind them, and keeping up a pretty decent clip while they’re doing it, too.

They’re not the most practical weapons ever, and spend much more of their time excavating civilian tunnels for Purely Peaceful Purposes than they ever do for military ones, but they have their uses, often when someone’s fortification needs to be reduced.