The M512 90mm SBHVC is the primary weapon of the M808B Main Battle Tank, and is mounted on the rear of the tank's chassis. The 90mm cannon is mounted in a fully-traversing turret mount, which allows the cannon to traverse 360 degrees horizontally and to depress from -10 to approximately +60 degrees vertically. 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 90mm High Velocity Cannon is fitted with an insulating thermal jacket to reduce gun-barrel warping caused by uneven thermal expansion. Unlike modern tanks however, the 90mm Cannon is mounted on the aft section of the Scorpion's chassis and contains no crew compartment, as the loading is done automatically and the targeting and firing is performed from the cockpit electronically.
The M512 uses a wide variety of 90mm ammunition, the most commonly employed of which is the 90mm tungsten Armor Piercing Ballistic Capped Round. This shell sacrifices armor penetration for larger amounts of high explosive filler. It is accelerated to a high velocity and can strike a target at extremely long ranges.[note 2] Another type of ammunition employed is the S1 Canister Shell, which provides increased 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.
The M512 can effectively destroy any light vehicle with only one shot. The cannon has very little recoil, which may be attributed to an added muzzle brake or to other aspects of its design. Even heavier vehicles like the Covenant Wraith can only withstand two to three rounds before being destroyed. Because of its large area-of-effect and high velocity, the cannon is a very useful anti-infantry weapon as well, able to kill even the toughest enemies (like Hunters) with a single blast.
In Gameplay the M512 is unable to fire at anything too close to the Scorpion, as the cannon cannot depress to that shallow an angle. The cannon's large area-of-effect means that precision kills are next to impossible - friendly infantry or vehicles near the target are as likely to feel the force of the blast as the intended target. The 90mm cannon must be reloaded after every shot and the process takes between three to four seconds. In the time it takes for the cannon to reload, the enemy may be able to take action against the tank, and the smoke trail the round leaves behind when fired announces the tank's location, making it easy for anti-armor units to target the Scorpion.
- Using the M512 in the level Delta Halo in Halo 2 will be tricky when the player moves into tight corners and when going up against Ghosts because of the steep angles. It is best for players to remain in one spot and let the Ghosts come to them.
- In Halo 3, the 90mm Cannon requires players to lead their target when engaging a mobile enemy like a Ghost or Banshee (move the reticle just slightly ahead of the target and fire). The speed at which the target is moving will inform the player as to how much of a lead is necessary.
- ↑ The 30 rounds per minute rate of fire is based off a calculation of 1 round fired every 2 seconds, 1 round fired every 2 seconds would come out to 30 rounds in 60 seconds. 30 × 2 = 60. This is based off of the reload time of the 90mm Cannon in Halo 3.
- ↑ In the Halo Universe, it appears that traditional shells have replaced the Armor Piercing Fin Stabilized Discarding Sabot Round used during the later half of the twentieth century. Whether this has to do with advances in ballistic performance, newer explosive materials, or different firing mechanisms is not known.
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