M370 autocannon

The 70mm chain gun is an anti-personnel/anti-vehicle weapon mounted below the nose of some D77-TC Pelican dropships.

Overview
The gun is linked to the movements of the pilot's head, which allows for very short delays between spotting enemies and firing, the turret will rotate up to 120 degrees to wherever the pilot is looking. However, the turret can also be operated by a copilot, or manually by a gunner.

This weapon fires very large 70mm shells. The rate of fire is most likely lower than most UNSC automatic weapons, though the shells certainly have heavy stopping power.

Trivia

 * While the weapon is said to be a chain gun (single barrel, few moving parts) the older older 40mm chin-mounted turret was said to be a rotary cannon (multiple rotating barrels, one barrel firing, higher rate of fire). This change is likely to compensate for the increased size of the projectile fired and the decrease in carried ammunition.
 * Though never seen in game, it is possible that this armament is used on Marine Corps Pelicans, while UNSC Air Force Pelicans are seen sporting the same chin-mounted M638 20mm cannon as the Falcon tiltrotors.

List of appearances

 * Halo: The Flood (Mentioned only)