M12G1 Gauss Warthog

The M12G1 Warthog LAAV, its turret is a Gauss Cannon that acts like a miniature Magnetic Accelerator Cannon and fires fast-moving projectiles, takes about a half of a second to reload and has unlimited ammunition like all vehicle-mounted weapons systems. Before the launch of Halo 2, it was hinted by Bungie that certain types of warthogs would also make it in the game: a moon variant, cargo variant, jungle variant, and snow variant.

(The Warthog in Halo 2 is much more maneuverable than in Halo with less sliding and an E-brake (left trigger) for easier stopping and tighter turns, which the Halo 1 Warthog seems to be doing all the time. It also has a horn (right trigger) which can be used for various reasons. Namely, taunting.)

The Warthog seen in the Halo 3 Multiplayer screenshot seems to be the same, but most likely (like everything else) will be slightly different in it's appearance/features from those in the other games.