Dirtworm

A dirtworm is a large mechanical device designed by goblin sappers during the First War to aid them in tunneling beneath Alliance defenses. Enormous teeth on the front of the device chew up earth and pull it inside, where steam hammers push it outward and compact it to create a tunnel with hard-packed walls. The dirtworm can chew through any material with low hardness at the rate of ten feet per minute. Harder materials take more time. The tunnel it carves is eight feet in diameter with walls of medium hardness; a five-foot length of the tunnel will collapse if it takes enough damage.