M68 Asynchronous Linear-Induction Motor

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 30,600 mph.The speed of the Gauss Cannon's projectile in-game is much slower than its canonical speed of Mach 40. This is probably due to design and engine limits. The projectile moves more quickly in Halo 3 than in Halo 2. 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 applied primarily in an anti-vehicle capacity 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 a 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, and can also be difficult to aim while the vehicle itself is in motion.

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.
 * 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 entirely vaporized on impact due to the projectile moving at over 44,880 ft/sec at the muzzle(over 22 times the speed of conventional munitions).
 * 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 and Halo: Reach, the slug in mid-flight is a blue mass with a blue trail. This 'blue light' is the slug heating the air around it and behind it to a ionized, super heated plasma state due to friction with the atmosphere. In Halo 2, the trail was yellow-orange.
 * A stationary version of the M68 Gauss Cannon as well as the M41 LAAG appears in Halo 3: ODST.
 * This version can be considered the UNSC's equivalent to the Covenant's Fuel Rod Shade.
 * In Halo: Reach, the projectile will bounce off of surfaces if fired at a certain angle and can penetrate any object that has been spawned in forge excluding "glass" items. (Window Double, Glass Cover, Glass Sail, etc.)
 * The Gauss cannon is said to have an extremely loud muzzle blast, this is actually a sonic boom created by the round as it is accelerated down the "barrel", the weapon itself is completely silent due to its electrical operating principle.
 * In Halo: Reach, the M68 is capable of penetrating completely through a Ghost if aimed at it's front "hood"
 * In Halo: Reach, the M68 seems to combine the best traits of two weapons, the penetration of the Spartan Laser and the "ricochet" ability of the Sniper Rifle.

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.