M1A1 Abrams

The M1A1 Abrams is an American main battle tank equipped with a 120mm smoothbore cannon, and a coaxial machine turret and is encountered numerously throughout the Black Mesa compound. The Abrams is used as the primary attack and defense vehicle by the HECU during the Black Mesa Incident to combat against the invading Xen and Race X aliens.

In Half-Life, the Abrams is first encountered in the chapter Surface Tension, providing fire support for a group of entrenched HECU soldiers. Another is stationed near the end of the chapter "Forget About Freeman!", blocking the entrance to the Black Mesa Central Complex. It differs from the first in a way that it also fires a machine gun. The tank is seen a third time near the end of the same chapter, this time with a mounted M2 machine gun on top, and the hatch open. It is unmanned, allowing the player to fire the 120mm cannon and the M2 at the incoming Vortigaunts and Alien Grunts.