M68 Gauss cannon

The M68 Asynchronous Linear-Induction Motor, more commonly known as the M68 Gauss Cannon, is a weapon that fires hyper-velocity, high-density projectiles similar to those of a Magnetic Accelerator Cannon, except on a much smaller scale. It can be mounted on a stationary stand, or on the rear of the M12G1 Warthog LAAV.

Operation
The M68 ALIM uses an asynchronous linear-induction motor to produce a bipolar magnetic field capable of launching a 25x130mm projectile at an incredible speed of just under Mach 40, or approximately 13.7km per second. The great velocity of the projectile is the key to the stopping power and performance of the Gauss cannon, giving it exceptional armor penetration.

Role
The M68 ALIM is primarily used in an anti-vehicle capacity used by UNSCDF ground forces, though it can be used to devastating effect against infantry. It is often seen mounted on the Warthog in the same manner as the M41 LAAG, and while it does not possess the LAAG's extreme rate of fire, it displays near-pinpoint accuracy and overwhelming firepower, usually killing infantry targets with a single shot, and heavily damaging those in the immediate vicinity of where the round impacts. Its intended usage is similar to that of a 102mm SC-HE Rocket Turret, though the rocket turret does not possess the all-around utility and adaptability of the M68 ALIM.

Advantages
The M68 is an extremely accurate weapon, useful against most enemy units. It has proven to be devastating against light-armored vehicles, it can take out a Ghost or a Banshee in one or two shots (depending on shot placement). The weapon is rather effective against Wraiths as well, provided the driver can out-flank the Wraith and fire upon its unprotected backside before it brings its plasma mortar to bear. The M68 is also very deadly if used against infantry, however users should aim at the most dangerous units like Sangheili, Jiralhanae and Mgalekgolo in order to make full use of the weapon.

Disadvantages
The M68 has few disadvantages, mainly the weapon's slow fire rate. It is also quite difficult to use at long ranges, especially when shooting at moving targets.

The Gauss Cannon can also cause permanent hearing damage when fired within 20 meters of unprotected infantry.

Tactics

 * The M68 is an excellent anti-vehicle weapon. It will get rid of enemy light armor rather quickly.
 * While not as effective against entire squads, it remains good against single infantry units.
 * Outstanding against Scarabs in Halo 3, since the Warthog on which the weapon is mounted is a smaller, faster target for it to hit. An effective tactic is to remain under the Scarab, avoiding the legs and the main gun, while your Marine gunner targets the Scarab's legs.
 * Experienced gunners using this weapon can effectively use the cannon's extremely high damage and accuracy to 1-shot kill most enemies. This has led to many Gauss gunners being able to attain high multi-kills and killing sprees, especially in multiplayer.

Appearances
In Halo 2, the M12G1 LAAV variant of the Warthog replaces the M12A1 LAAV version of the Warthog, which was featured in Halo PC. The M12A1 LAAV 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 (one of which triggers the flashback level Kizingo Boulevard) appears in Halo 3: ODST. The M68 can also be used near the start of ONI Alpha Site. In Halo Wars, the Gauss Turret is the final upgrade to the Warthog. It allows for much greater offensive and defensive capabilities.

Miscellaneous

 * 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.
 * In Halo 3, the screen on the cannon's firing mechanism will actually display its surroundings in real-time thermal imaging, similar to the scope of the Sniper Rifle System 99D-S2 Anti-Matériel. Unfortunately, this does not have any effect on gameplay, and is only in place for aesthetic reasons.
 * 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. In Halo 2, the trail was yellow-orange.
 * In Halo: Reach, the projectile will bounce off of surfaces if fired at a certain angle.

Production notes

 * 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.
 * The Halo 3 version of the Gauss Cannon is a bit weaker and has a slower rate of fire than its Halo 2 version. Part of this reason is gameplay balance since the Halo 2 version was allegedly claimed to be too powerful in-game.
 * Though thought to be similar to the LRG Rail Gun, the primary armament of the Cobra artillery vehicle seen in Halo Wars, the Gauss Cannon actually functions on a completely different principle. A railgun simply uses an electrical current to force a magnetic projectile along using the principle of same-pole repulsion; a more complex coilgun, or Gauss gun as it is known in Halo, uses multiple coils to accelerate the projectile through the weapon.