|First Appearance||The Nightmare Begins|
The Frontline BattleMech is what Zim used to lay waste to Irk, albeit unintentionally.
The BattleMech is a gigantic humanoid device, colored reddish purple. It requires three pilots to operate. The Frontline BattleMech appears to be one of the most powerful of all Irken military units, perhaps only comparable to the Massive.
Zim commanded one during Operation Impending Doom I, but got so excited he forgot that he hadn't left Irk yet, and proceeded to destroy the entire Irken army, thus earning himself his reputation as the worst Invader ever, as seen in the series premiere, "The Nightmare Begins".
Zim was banished to planet Foodcourtia after the incident, but "quit" being banished after hearing of Operation Impending Doom II. The Frontline BattleMech has not appeared since, although it was scheduled to make a re-appearance in a flashback during the cancelled episode "The Trial."
So far, only one (the one that Zim practically destroyed Irk with) has been seen in the series, but there may have been more than just one.