M203 grenade launcher

The M203 grenade launcher is a single shot 40 mm grenade launcher designed to be attached to an assault rifle, such as the M4 or the M16.

Development/Usage
It was designed between 1968-1969, and was issued into service during the 1970s. It was also the only one of the SPIW (Special Purpose Individual Weapons) to actually be developed and mass-produced. Consequentially, it replaced the M79 grenade launcher as well as the conceptually similar Colt XM148 design.

The rogue FOX member Python utilized a M203 grenade launcher attached to an M16A1 assault rifle. It was specially modified to fire liquid-nitrogen grenades that contain enough of the substance to instantly freeze another soldier's weapons. He later attempted to use this weapon on Big Boss and his resistance, although he was ultimately defeated.

The Militaires Sans Frontieres developed the M203 grenade launcher-equipped versions of the M16A1 and the M653 assault rifles after finding design specs for them. They could fire grenades of frag, smoke, and stun variants.

Post-Peace Walker
Eventually, the M320 grenade launcher was developed so it would in the future replace the aging M203 grenade launchers.

During the Big Shell Incident, the M203 grenade launcher, alongside its successor, the M320, were utilized as attachments to the attack teams' M4 carbine rifles.