M655 machine gun

The M655 Heavy Machine Gun/Anti-Matériel is a 20mm heavy machine gun used by the UNSC. Some versions of the Mark IX "Mantis" powered exoskeleton are armed with an M655 as well as an M5920 surface-to-ground missile launcher.

Trivia

 * Under modern military conventions, the M655's 20mm caliber would actually classify it as an autocannon.
 * In gameplay, the M655's barrels do not spin when the weapon is fired.

List of appearances

 * Halo 4
 * Spartan Ops
 * Halo: Escalation
 * Halo 5: Guardians