M68 Gauss cannon
From Halopedia, the Halo wiki
Summary
The M68 Gauss Cannon is a vehicle mounted weapon. Asychronous linear-induction motor produces bipolar magnetic field to fire 25mm projectile at hyper-sonic velocity. It is usually found on Warthogs. The Gauss Cannon is an extremely good weapon for its type and is effective against all types of vehicles. In multiplayer, this weapon can also scare new players out of cover, allowing a passenger to kill him.
