With the M203, the U.S. Finally Got a Decent Grenade-Launcher
The AAI design replaced Colt's disappointing XM148
In May 1963, the U.S. military asked industry to supply an underslung grenade launcher to complement the new AR-15 assault rifle that was then in early testing. The grenade-launcher program had its roots in the ultimately unsuccessful Special Purpose Individual Weapon program that had begun in 1951.
In May 1964 Colt offered its design — the CGL-4. The Army tested the CGL-4 alongside competing designs from Springfield Armory and Ford. A fourth design from AAI was promising but couldn’t chamber the Army’s standard 40-by-46-millimeter round, so the Ordnance Corps rejected it.
The CGL-4 underwent extensive testing between 1965 and 1967 under the designation XM148. Colt manufactured a startling 27,400 XM148s — many wound up in Vietnam for field testing. Despite Colt’s efforts to rectify a growing list of problems, the Army concept team in Vietnam ultimately deemed the XM148 unsatisfactory and recommended removing it from service.
Shortly thereafter, the Army launched development of a new and improved launcher.
While the XM148 proved to be a failure, it did at least prove the operational viability of an underslung, rifle-mounted grenade launcher.
The Army launched the new Grenade Launcher Attachment Development program in the summer of 1967. Several manufacturers submitted designs. Colt offered Henry Into’s CGL-5. The Army turned down Colt’s offer of 20 free CGL-5s and outright rejected the design.
A Colt CGL-4/XM148 in Vietnam. Source
The earlier AAI design came roaring back, now designated XM203 and chambering the 40-by-46-millimeter shell. Among the competing GLAD designs, the XM203 quickly proved to be the best-performing and most cost-effective. The Army selected the XM203 for field trials in August 1968 and, in November, placed an initial order for 500 copies.
The first XM203s reached U.S. units in Vietnam in April 1969. Troops liked it for its robustness — and because it was less prone to snagging on kit and brush than the XM148 had been. Following a three-month combat evaluation, the Army formally adopted the M203 in July 1969.
The 15-inch M203 weighs three pounds. It’s a single-shot, pump-action launcher. The operator unlocks the breech and pushes the barrel forward to open the action. It chambers a variety of 40-millimeter rounds, ranging from high explosive and buckshot to illumination rounds and smoke grenades.
The M203 is much simpler than the XM148 was. Its front ladder sight can be used in conjunction with an M16′s iron sights — or the operator can attach a more complex quadrant sight.
Ironically, as AAI was predominantly a research-and-development company, in 1971 the Army contracted with Colt to build the M203. Since then, various companies have produced more than half a million M203s. A number of countries have fitted the launcher to a wide variety of rifles including the Steyr AUG and Daewoo K2.
As of mid-2017, the United States plans to phase out the M203 in favor of Heckler & Koch’s new M320.