Siege Tank
Damage: 30+9 (w/upgrades) (splash damage)
Siege Mode: 70+15 (w/upgrades) (splash damage)
Armor 1+3 (w/upgrades)

The Siege Tank is the backbone of the enterprising Terran general's army. Cheap, easily upgradeable, and power all distinguish the Siege Tank from other Terran units. The Siege Tank also possesses the unique quality of being able to fire its cannons while at full speed - drive-by shooting, anyone?

But what really sets the Siege Tank apart from other units, though, is its Siege Mode ability. Siege Mode must be researched at a Machine shop before it can be used; fortunately it's cheap and is quickly researched. Once Siege Mode is available and used, the tank is immobilized - but it transforms into a sort of artillery for the Terran commander. Indeed, a group of Siege Tanks in Siege Mode is enough to wipe out a Hydralisk rush, depending on the size. More tanks are needed for a Dragoon rush, due to their shields. A Siege Tank upgraded to Level 3 can do a whopping 85 points of damage in Siege Mode

The Siege Tank, however, is defenseless against airborne attacks; despite the fact that the Siege Tank's cannon is clearly pointing UPWARDS, it is unable to attack any air units. A group of Guardians will make quick work of any unprotected Siege Tanks. Self-destruction is also common amongst Siege Tanks - they will not fire if an attacking unit is too close, but other tanks will fire, destroying themselves thanks to splash damage