M68 Gauss cannon

The M68 Asynchronous Linear-Induction Motor, more commonly known as the M68 Gauss Cannon (named after nineteenth century physicist Carl F. Gauss), 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 at impressive ranges.

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 and causes much more collateral damage.

Advantages
The M68 is an extremely accurate weapon, useful against most enemy infantry and vehicle units. Unsurprisingly 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. Firing at the vehicle's armored front is less effective, but the rate at which the weapon cycles can compensate for this. 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 before moving onto smaller, less dangerous targets. Its relatively high rate of fire, when compared to other electromagnetic accelerator weapons, makes it a devastating precision weapon on any battlefield. Its anti-armor capabilities are second only to those of the SP42 Cobra's mounted M66 light rail gun, and static defense platforms, such as the Onager, and its portability more than makes up for this.

Disadvantages
The M68 has few disadvantages, mainly the fact that the weapon (like all other vehicle-mounted turrets) offers little to no protection to the operator, and allows them to be easily sniped without the presence of a skilled driver. It lacks precision at extreme distances, but can still hit large targets (i.e. Wraiths and Phantoms) with a fair degree of accuracy. The Gauss Cannon can also cause permanent hearing damage when fired within 20 meters of unprotected infantry. The M68's muzzle flash can also give away its user's position.

Tactics

 * The M68 is (unsurprisingly) 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. Doing this with a co-op player is even more effective.
 * 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. Perfections are also not unheard of, especially if the hog the cannon is mounted on is parked away from the main battlefield.

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.
 * In Halo: Reach, if one looks at the screen of the cannon, they could see the original Xbox logo.

Production notes

 * During the Halo 2 demo trailer, the M68 Gauss cannon 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 M68 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.

List of appearances

 * Halo 2
 * Halo: Uprising
 * Halo 3
 * Halo Wars
 * Halo 3: ODST
 * Halo: Evolutions - Essential Tales of the Halo Universe
 * Palace Hotel
 * Halo: Reach
 * Halo 4
 * Spartan Ops
 * Halo 2: Anniversary