M68 Gauss cannon

The M68 Gauss Cannon is a weapon that fires hyper-velocity, high-density projectiles similar to those of a MAC gun, except on a much smaller scale. It is mounted on the rear of the M12G1 Warthog LAAV, and sometimes it can be found mounted on bridges, roofs, etc.

It is very powerful and very useful against vehicles. However, it is not as effective against infantry as the M41 LAAG, which is also mounted on the Warthog. This is because there is little splash damage and it has a slower rate of fire, but a direct hit will kill most enemies in one shot, or two if the target has an overshield. Due to its power and reasonable rate of fire it is a good weapon against Wraiths and many other vehicles. Its intended usage is similar to that of the 102mm SC-HE Rocket Turret.

This weapon uses an Asynchronous Linear-Induction Motor to produce a bipolar magnetic field capable of launching a 25mm x 130 projectile at hyper-sonic velocities. The great velocity of the projectile is the key to the stopping power and performance of the Gauss cannon, giving it exceptional armor penetration. As such, it is a commonly used anti-vehicle weapon of the UNSC Marine Corps. However, the M68 can also be used to eliminate Covenant infantry units with reasonable effectiveness.

In Halo 2, the M12G1 LAAV variant of the Warthog replaces the M12A1 LAAV version of the Warthog, which was featured in Halo PC. That version became problematic due to the prodigious reload time necessary for the launchers, and the slow speed of the rockets themselves, although it did not appear in the campaign. A stationary version of the M68 appears in Halo 3: ODST.

The predecessor to the M68 Gauss Cannon was the M66, the primary armament of the Cobra artillery vehicle seen in Halo Wars. The M66's were much larger and bulkier, though they made up for this by being able to fire heavier rounds.

Trivia

 * While operating on a similar principle to the M99 SASR, the shells for the M68 appear to be designed to cause hypervelocity collisions, where the target and slug get almost entirely vaporized on impact. This is probably intended to reduce over-penetration.
 * During the Halo 2 demo trailer, the Gauss fired at a fairly rapid speed. Later, in an early beta multiplayer phase the M68 seemed to be slowed down and also seemed to have lost all its hype. It was later revamped with its original rate of fire during the game's final stages
 * In Halo 3, the slug in mid-flight is blue with a blue tail, making it look like Covenant weapon's fire at first glance. This 'blue light' is most likely the slug heating the air around it to super heated levels due to friction with the atmosphere.
 * The Halo 3 version of the Gauss Cannon is weaker and has a slower rate of fire. This came in to balance, since Halo 2 Gauss Cannon was allegedly too powerful in-game, though it is still devastating in combat.
 * Ferrex said in a thread, "While the Warthog Gauss rifle is modeled as a magnetic acceleration cannon, the sound and effects are actually those of a railgun, which operates on a different principle. However, the sound and effects were so cool that we couldn't not use them."
 * In the Halo 3: ODST gameplay trailer on the Xbox Live Marketplace, footage of a mounted version of the Gauss Cannon has been shown.
 * It is featured as an EMP cannon in the popular web series Red vs. Blue