UH-1B/UH-1C "Hueys" were used with moderate success as a gun ship with door mounting M60D 7.62 machine guns on the M23 armament subsystem. They could also be armed with a pod or side-mounting six-barrel "Minigun" and seven-tube XM157 or XM158 2.75 inch (70mm) rocket launcher on the Emerson Electric M21 armament subsystem, and the M5 chin-turret mount for a 40mm grenade launcher. The UH-1B was also armed with two fixed-mounting M24A1 20mm cannon on the XM31 armament subsystem. The M60A1 reflex sight was used for sighting guns and rockets on the UH-1B, UH-1C, and UH-1M "Huey". With the fielding of the larger UH-1D as the Army's primary utility helicopter, the smaller UH-1Bs/UH-1Cs assumed the gunship role as their primary mission.