M410 flank gun
From Halopedia, the Halo wiki
The M410 40mm dual heavy machine gun/flank mounted, shorter form M410 heavy machine gun, and colloquially referred to as the flank gun, is a heavy machine gun in service with the UNSC Armed Forces during the conflicts in the years following the Human-Covenant War.
The M410 is commonly fixed to the main fuselage of the Gunship 79 Heavy Troop Carrier/Mobile Armory, the gunship variant of the D79-TC Pelican. It fires 40mm gas-jacketed, depleted uranium rounds. These can be used to tear through enemy infantry and vehicles alike, no matter the environmental conditions.
The operator sits in a bucket-seat and they generally provide ground support cover during deployment and exfiltration of military personnel. The weapon is also useful for flanking lines of fire from the Pelican's blind spots. Controlled by a Spartan, the flank gun may be used to combat enemy aircraft high above a planet's surface, and can even be used in rare exoatmospheric scenarios. However manning an M410 is always risky, as the operator is exposed to enemy fire and there is no formal way to return to the vehicle's bay.
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