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SOG teams were some of the first to use the XM203 under-barrel grenade launcher. The M203 grenade launcher had been developed between 1967 and 1968 by the AAI Corporation of USA on  contract from US Army. This contract had been issued on the basis of the experience gained by the US armed forces in Vietnam with the M79 40mm grenade launcher (which was successful design but required an additional personal defense weapon to be carried by the grenadier) and the unsuccessful XM-148/CG-4 40mm under-barrel grenade launcher, developed in mid-sixties by Colt in an attempt to cure deficiencies of the M79. The new grenade launcher was intended to be used with all available 40mm ammunition, and to be attached to the existing infantry rifle then in service, the M16A1. In late 1968 the AAI design had been type classified as XM203, and in early 1970 the first M203 units were sent to Vietnam for field evaluation. After successful tests the US Army ordered large quantities of the M203, and since AAI had no resources for mass production, the manufacturing contract was issued to Colt. later on, more or less exact copies of the M203 were produced in Egypt, South Korea and Bulgaria (as UBGL-M1, with mounts suitable for Kalashnikov AKM and AK-74 type rifles). During the 1990s, the M203 went into several modifications, such as the shorter barrelled M203A2 (with a 9 inch barrel, as opposed to the standard 12 inch barrel), intended for shorter M4 carbines used by US SOCOM, as well as versions with MIL-STD 1913 (Picatinny rail) compatible mounts. The M203 launcher is still being used by US armed forces, and by many other military’s, including those of Australia, Israel, South Korea, Philippines and Turkey.

The M203 is a single-shot, breech-loading weapon with rifled barrel. The loading is achieved by sliding the aluminium barrel forward, then inserting the round of ammunition into the breech and then sliding the loaded barrel back into the battery. The barrel is held in-battery by the manually controlled lock, which is disengaged by depressing the barrel catch lever on the left side of the launcher, above the middle of the barrel. The loaded cartridge is held at the breech face by the extractor claws, and remains stationary when barrel is opened forward. Once the barrel clears the fired case or unfired round, it is free to fall down from the breech face, so the next round can be loaded if necessary. The self-cocking firing unit with its own trigger is located at the rear of the M203 receiver, also made from aluminium alloy. The manual safety in the form of the swinging flap is located inside the trigger guard, just ahead of the trigger. The rear part of the barrel is covered with a polymer handgrip. The standard M203 easily installs on the M16A1 or M16A2 type rifle, and installation requires about 5 minutes of work and a standard screwdriver for clamping screws. If necessary, the M203 can be mounted on a separate shoulder-stock / pistol grip assembly (available from several companies, such as Colt or Knight’s Armament) to be used as a stand-alone weapon. Standard sights for the M203 are of ladder type, and graduated from 50 to 250 meters in 50 meter increments. The optional quadrant sight can be installed on the left side of the M16A1/A2 carrying handle, and it allows aiming at ranges of up to 400 meters.