Plasma mortar

The 'Plasma Mortar' is the primary weapon of the Wraith and the Covenant Air Artillery.

Introduction
The Plasma mortar fires huge balls of slowly moving superheated light-blue plasma with a large explosion radius and slow rate of fire. It is extremely powerful and usually kills in a single hit and can destroy just about anything on the battlefield in a minimal amount of shots. It uses indirect fire, like the Fuel Rod Gun, meaning that it can be fired just about anywhere on a battlefield without having to worry about obstructions such as hills.

Tactics
While in Wraiths, the Elites and Brutes that drive them usually use the plasma mortar at far distances. As the plasma is affected by gravity, meaning that it is shot at an arc, the driver always aims higher than the enemy, and always at long distances. In Halo 2 they are equipped with automated plasma cannons that only an AI can use. These are replaced in Halo 3 with a plasma turret that can be opperated by another player. If you are found going head-to-head with a Wraith, it is advised not to openly challenge the driver, that is unless you have heavy weapons to back your confrontation. (I.E. Rocket Launcher, Fuel Rod Cannon, Missile Pod) Get close to the Wraith but watch the arching plasma bolt, board the Wraith, stick with a grenade, or just punch the driver out.

Covenant Artillery
A giant stationary plasma mortar was seen destroying buildings in the Halo 2 E3 Demo video. Sergeant Banks called in an airstrike and a group of Longsword fighters flew in and destroyed it.