A twin rocket tank, which can do pretty heavy damage.
Its slow moving speed and fire rate makes it susceptible to groups of fast moving units like Pawns, but once it shoots it deals damage in a massive radius, which can eliminate virtually all bots (except Centurions) in a single blow. Combine with Whistlers (missile trucks) and repairing units to achieve devastating effect on enemy defenses.
It is also a perfect unit for destroying Commanders, as only 5 shots is enough to deal lethal damage.
It requires some good micro, so focus!