M512 smooth-bore high-velocity cannon

The M512 smooth-bore high-velocity cannon, or simply the M512 cannon, is a 90mm gun mounted on the M808 and M808B Scorpion tanks.

Design details
The M512 cannon is mounted on the rear of the tank's chassis. The weapon's design remains for the most part unchanged from 20th century tanks: the M512 cannon is mounted in a fully traversing turret weapon mount which allows the cannon to rotate 360 degrees and to move -10 to approximately +60 traverse. A gyroscope is used to stabilize the cannon, allowing it to be effectively aimed and fired at the "short halt" or on the move.

The M512 cannon is fitted with insulating thermal jackets to reduce gun-barrel warping caused by uneven thermal expansion. Unlike modern tanks however, the M512 cannon is mounted on the aft section of the Scorpion's chassis and contains no crew compartment as the loading is handled by an autoloader system and the targeting and firing is done electronically from the crew compartment.

Ammunition
The M512 cannon can be fitted with a wide variety of 90mm ammunition. The most commonly employed round is the 90mm tungsten armor-piercing ballistic-capped round. This type of round sacrifices armor penetration for larger amounts high explosive filler, this round is accelerated at a high velocity and can strike a target at extremely long ranges.

Another type of ammunition employed is the S1 Canister Shell, the S1 Canister provides Scorpion equipped tanks with destructive capabilities without the use of traditional high explosives. The Canister round is lethal against enemy infantry when machine guns or other weaponry cannot be used effectively. The S1 is also effective at breaching walls and damaging structures or other vehicles.

Advantages
The M512 cannon can effectively destroy any light vehicle with only one shot, the cannon has very little recoil and may be attributed to an added muzzle brake or its design, even heavy vehicles like the Covenant Type-26 Wraith can only withstand two-three rounds before being destroyed. Because of its high area-of-effect and high velocity it is a very useful anti infantry weapon as well, able to kill even the toughest infantry like the Mgalekgolo in just one shot. One shot from a 90mm Cannon is also very effective at destroying walls or structures if enough shots are fired at it.

Disadvantages
The M512 cannon is unable to fire on anything too close to the cannon, or the Scorpion's chassis, as the cannon cannot traverse that close. The cannons high area-of-effect means that precision kills are next to impossible - friendly infantry or vehicles near the target are likely to feel the force of the blast as much as the intended target. The M512 cannon must be reloaded after every shot and takes between three to four seconds, the time it takes for the cannon to reload may give the enemy enough time to react against the tank; and the smoke trail the round leaves behind when fired, compromises the tanks location making it easy for enemy anti-armor personnel to locate the Scorpion.

Campaign

 * In Halo: Combat Evolved, the cannon is quite inaccurate, so targets that are located at the bottom of the reticule would be hit.
 * Using the M512 in the level Delta Halo in Halo 2 will be tricky when the player moves into tight coursers and going up against Type-32 Ghosts because of the steep angles. It is best for players to remain in an open spot and let the Ghosts come to the player. If this option is not available it is recommended that players use the Scorpion's turret machine gun instead.

Multiplayer

 * In Halo 3, the 90mm cannon requires players to lead their shot against moving targets move the reticule just slightly ahead of the target and fire. When going up against aircraft like the AV-14 Hornet or the Type-26 Banshee, players must also aim ahead of their target. Depending on how fast the target is moving, the reticule needs to be slightly ahead of the target or just outside the reticule.
 * In Halo 4, the cannon produces a noticeable vapor trail similar to that of a sniper rifle when fired upon and reveals the tank's location. The cannon's velocity travels a fraction of the speed that it was in Halo: Reach. Also, unlike previous Halo titles, the tank round can be bounced off in several odd occasions and arc over long distances.

List of Appearances

 * Halo: Combat Evolved
 * Halo 2
 * Halo 3
 * Halo Wars
 * Halo 3: ODST
 * Halo: Reach
 * Halo: Combat Evolved Anniversary
 * Halo 4
 * Spartan Ops
 * Halo: Spartan Assault
 * Halo 2 Anniversary