Type-27 Anti-Aircraft Cannon

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"They're setting up an AA battery. That thing'll tear the Dawn apart..."

- ODST

The Anti-Aircraft Battery is a Covenant ground-based stationary anti-aircraft emplacement. It fires bolts of plasma that are extremely damaging. A single round can destroy a C709 Longsword-class Interceptor, or even a UNSC Frigate.

Background
The bolts fired by the Anti-Aircraft Battery are in a teardrop shape, similar to normal plasma rounds and fly in a straight trajectory. The plasma bolts are extremely powerful, since even their wake is able to take down a Longsword. It is unclear about how powerful these weapons are; during the Battle of Installation 00, an it was reported that one AA gun could "tear the Dawn apart", implying that an AA battery would be powerful enough to destroy a UNSC Frigate.

However, the battery must cool off and release its excess heat after every shot, exposing the its weak point; the interior is vulnerable through a vent on the underside the gun. A certain amount of damage to the interior will destroy the AA battery, making it vulnerable to infantry and ground vehicle attacks. Troops are often stationed on and around AA guns to safeguard them from ground forces.

An AA battery can be quickly assembled using modules transported by Phantoms. This makes them easy to deploy in the field. AA batteries are also often supplemented by deploying multiple Anti-Air Wraiths nearby.

History
The AA battery saw use during the Battle of Voi on November 17th, 2552, when one battery had been deployed in the town of Voi in order to keep the UNSC forces away from the Portal excavation. The UNSC planned a low-level strike, using Frigates and Longswords, to attack the Prophet of Truth's Forerunner Dreadnought which was resting on the Portal, which was thought to be the Ark by the UNSC at the time. Throughout the battle, the AA battery fired continuously, and managed to destroy at least one Longsword. Marines and SPARTAN-117 eventually breached the Covenant resistance in Voi and destroyed the AA gun, allowing Lord Hood's ships to assault the Forerunner Dreadnought.

AA guns were also used during the Battle of Installation 00, when the Covenant tried to construct them on the surface of the Ark to keep the UNSC ships above from reinforcing their troops on the ground. However, these batteries remained incomplete, as SPARTAN-117 with the assistance of several Orbital Drop Shock Troopers stopped their construction, allowing the to land nearby.

Appearances
Anti-Aircraft batteries appear only in Halo 3. In the level The Storm, the main objective is to destroy the AA gun in Voi so that Lord Hood can start attacking the Prophet of Truth's Dreadnought. Two AA Batteries under construction also appear in the level The Ark.

The AA battery shares some features with to the Covenant Artillery, which was introduced in the Halo 2 E3 Demo and later seen in Halo 2, though inactive. Though a certain resemblance can be seen between the Artillery piece and the AA battery, their roles differ greatly; while the former fires large Plasma Mortar bolts in arced trajectories, the latter serves exclusively as an anti-air weapon.