M71 Scythe

Were you looking for the M41 Light Anti-Aircraft Gun, which is sometimes called the Vulcan?

The Vulcan anti-aircraft turret is a weapons emplacement used by the United Nations Space Command. It was produced by Misriah Armory on Reach and was fed by a 1,000-round Galilean ammunition drum. It also features an M41 "SPNKr" rocket launcher.

Multiple such turrets were placed around the Office of Naval Intelligence's Sword Base on Reach. One such turret was located at Airview Base. On July 26th, 2552, Catherine-B320 and SPARTAN-B312 were ordered to Airview Base to reactivate the turret. These turrets were also seen defending the Sabre Program Launch/Research Range from Seraphs and Spirits, capable of taking them out effectively.

Trivia

 * The turret is ostensibly named after the M61 Vulcan, a modern-day Gatling-style weapon.
 * There are several inconsistencies in the appearance of the gun. Because the gun is designed like a Gatling gun, with multiple barrels, its purpose is most likely to attain extremely high rates of fire from 4,000 to 10,000 rounds per minute. However, the gun depicted in the game shoots several individual rounds with deep booms, then immediately begins spinning at an extremely high rate without firing. The design should spin at the high rate and make a loud, deep buzzing sound, due to dozens of rounds being fired per second. This is either an oversight by Bungie or a gameplay factor not fully corrected. Since it is described as being fed by a 1,000 round drum, it was most likely not intended to be a gatling gun in the final version of the game, but earlier concepts may have had it being one and a last minute change was made to it's mechanics, but not to its appearance.
 * In rare instances, the rotating turret can fall from the rest of the weapon and continue to fire at enemy aircraft. When detached, it rolls around and can be pushed with a vehicle.

List of appearances

 * Halo: Reach