The M638 Autocannon is used as both an anti-personnel and anti-armor weapon, and is exclusively mounted on the UH-144 Falcon. It fires explosive rounds that can wound targets close to their blast radius and cause heavy damage to armored targets as well. It is effective against both infantry and stationary gun emplacements such as the Shade turret, and is powerful enough to allow a Falcon to hold its own in a dogfight against multiple Banshees. Sustained fire from an M638 is even capable of destroying Phantom dropships. The autocannon fires in 5 round bursts, and only needs 3 or 4 to eliminate a Banshee on most difficulties.
Strangely, for a large caliber weapon with a high rate of fire, it does not overheat, even after minutes of continuous firing. This is likely due to the fact that it only fires in bursts, which allows it to dissipate heat in between shots.
- Halo: Reach Official Strategy Guide - page 343