Skar'wa-pattern Mantis

You may be looking for the related article: Covenant Air Artillery The Anti-Aircraft Battery is a Covenant Loyalist ground-based stationary anti-aircraft emplacement.

It fires bolts of plasma that is extremely damaging. A single bolt can destroy an entire aircraft.

Halo 2 E3 Demo
The Covenant Artillery was first seen in the Halo 2 E3 Demo. When the Covenant invaded Mombasa, they stationed a handful of artillery pieces on the ground, which demolished UNSC buildings. Eventually, SPARTAN-117 and his group of Marines encountered one, and Sergeant Banks called in a Longsword air strike to destroy the stationary mortar. They fired plasma bolts similar to that of Wraiths, and in indirect parabolic trajectories.

Halo 2
The roles of the Covenant Artillery pieces as an active part of the Covenant assault were greatly downgraded in Halo 2, as the entire First Battle of Earth was downgraded. The Covenant apparently placed several artillery pieces on the beachheads of New Mombasa, but did not fire them.

Halo 3
The Covenant Artillery can be seen in the level The Storm, and is the main objective of the level, which is to destroy it so that Lord Hood can start attacking Truth's ships. This time, the bolts that it fires are in a teardrop shape similar to shade and plasma rounds, and in an almost straight trajectory. One in construction can be seen in the level The Ark.