Be aware that aggressive named mobs are infamous for having a zone-wide range and often cannot be "run off", so avoid named mobs as much as possible. Also, in some games aggressive mobs can be scraped off on other players. Running your train over other players to scrape them off in this way is considered very rude, even illegal in some games and may get you sanctioned by the GMs.
The name comes from the appearance to a casual observer. The tank looks like the locomotive with the persuing mobs following like train cars on a track.
Choo-choo! Train to zone!