The Colt CGL-4 grenade launcher was developed by the famous Colt company in the 1963, upon request from the US Army for a rifle-mounted 40 mm grenade launcher. The idea was to replace a relatively new stand-alone 40mm M79 grenade launcher with a combination weapon that would allow a single soldier to operate effectively both as a rifleman and as a grenadier. Similar concept was being developed at the time under the SPIW program, but US army also wanted a simpler and cheaper system as an interim solution.
The first Colt CGL-4 grenade launchers were ready for trials in 1964, and in early 1965 US Army ordered the first batch of 30 new weapons of this type for the field tests. The army assigned the Colt CGL-4 grenade launcher an official index XM148. Following the intensification of the Vietnam war, in early 1966 the US MoD ordered more than 10 thousand of the new weapons to be used along with the Colt XM16E1 and M16A1 rifles.
The new M16 rifle was the primary mounting platform for the Colt CGL-4 / XM148 grenade launcher, but there were other hosts as well. Australian Army units, which operated in Vietnam, acquired some XM148 launchers and mounted them on their 7.62mm L1A1 SLR rifles.
It must be noted that the Colt grenade launcher did not fare well during the jungle war. It was too complex and required extensive maintenance. Its sights and long trigger tended to catch up on clothing, webbing gear and vegetation, and the entire system was not very durable. As such, the US Army declared the Colt CGL-4 / XM148 underbarrel grenade launcher obsolete and withdrew it from the front-line service. It was promptly replaced with the more robust and efficient 40mm M203 grenade launcher, which was developed by the AAI and mass-produced by the Colt.
The Colt CGL-4 / XM148 grenade launcher is a single shot weapon which is normally mounted below the barrel of a host rifle, using special mounting brackets, provided with the launcher. It features a forward-sliding barrel, mounted inside a stationary outer housing. Both the housing and the barrel are made from an aluminum alloy. To load the launcher, user has to disengage the barrel lock, located near the small grip protruding down from the barrel, and push it forward. A large opening at the bottom of the barrel jacket allows for ejection of the fired case and manual loading of the fresh round. Once the new round is chambered into the barrel, it can be slid back and locked to the stationary breech. The trigger is of single action type. Striker must be cocked manually for each shot using a cocking knob that protrudes back from the breech of the gun. The trigger is mounted on a long strut, made from the steel wire, to place it close to the rifle’s trigger for faster transition between rifle and grenade fire. When not in use, the trigger can be rotated up to rest along the upper receiver side of the rifle. Iron sights are mounted on the left side of the weapon.
Colt CGL-4 / XM148 grenade launcher, basic specifications: