The M79 was one of two 40mm grenade launchers in common use by Allied forces in Vietnam.
November 18, 2024
By Will Dabbs, MD
CWO2 Ryan Arntson slowed his OH6A Loach to a crawl just above the treetops and nudged a little right peddle to put the helicopter into a crab. Arntson and his aerial observer SPC4 Terry Pollard both sat on the right side of the aircraft. They had flown together as a crew for four months now, a literal lifetime in combat, and knew each other better than brothers. Their Loach had not worn doors since it arrived in country. Counterbalancing the crew on the left side of the little machine was an XM27 minigun system along with 2,000 rounds of 7.62x51mm ammunition. Both men searched the tangled jungle underbrush for signs of NVA activity. The AH1G Cobra that made up the other half of their Pink Team orbited at 1,500 feet like some kind of ravenous predator awaiting the chance to strike.
The M79 40mm grenade launcher offered unrivalled versatility to the troops who used it in the 1960’s. Pollard saw it first. The dark gash amidst the otherwise random jumble of brush seemed out of place. Arntson slid the Loach sideways so they could get a better look, and they saw the black void of the firing port of a well-concealed bunker. The chatter was constant between Arntson and Pollard as well as between Arntson and the orbiting Snake. Pollard released his chopped M60 on its bungee cord and lifted the M79 grenade launcher from where it hung by its sling on the back of the pilot’s seat armor. Arntson held the Loach steady as a stone while Pollard sighted the stubby barrel by rote.
The Hughes OH6A Light Observation Helicopter was universally referred to as the Loach by those who flew and serviced it. (Wikipedia photos by Airwolfhound). The Loach was a small, nimble, fast aeroscout helicopter. (DOD photo). The M79 was a popular weapon with both US and Allied troops fighting in Vietnam. (DOD photos) Terry Pollard had long since outgrown the Blooper’s complicated ladder sight. He had tossed enough rounds downrange to be able to gauge proper elevation and windage on the fly, even from a hovering helicopter. He pulled the stubby little howitzer into his shoulder, judged the distance, thumbed off the safety, and squeezed the trigger. The soft report of the M79 was lost in the rotor noise. The little high explosive grenade looked like a gigantic horsefly as it arced into the dark void of the bunker. There was a quick flash from inside the structure, and smoke poured out of half a dozen hidden openings. Then the world exploded.
Green tracers clawed up from the jungle like angry bees. Arntson felt rounds connecting with his aircraft as he laid the nimble little Loach on its side. Pollard tossed the M79 behind him and stood up behind his M60, straining to get a proper angle during the vicious bank. Pollard torqued on the trigger as Arntson pulled the aircraft back level, lighting up his minigun as he turned. The Loach’s hyperactive Gatling gun and Pollard’s M60 synergistically tore the jungle to pieces. In moments they were clear and the hungry Snake rolled hot with 2.75-inch rockets as well as a pair of miniguns of its own. Pollard stowed his grenade launcher, and Arntson made a beeline for nearby Khe Sanh. Their Loach had picked up a nasty shudder, but the old girl would get them home all the same.
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The Tactical Revolution The barrel release and safety are right where you’d expect them to be. The stubby 40x46mm M433 round fired by the M79 employs a surprising lot of technology. The expansive ladder sight on the M79 was effective if a bit cumbersome. The war in Vietnam marked a stark military transition from the brute force strategy of World War 2 to the high-tech world of today. Vietnam saw the widespread introduction of night vision systems, precision-guided munitions, lightweight assault rifles, and helicopter warfare. In many cases, there was no published doctrine. US troops just figured it out as they went along. In no place was this more apparent than in airmobile operations with combat helicopters. Loach crews were the lunatic rock stars of Army Aviation. With a main rotor diameter of a mere 24 feet, their little OH6A Light Observation Helicopters could get into some remarkably tight spaces. Engagement distances were frequently measured in feet, and it was not unknown for Loach crews to return from a mission with blood on their windscreens. Of 1,419 Loaches delivered to the Army, 842 were destroyed in Vietnam. Loach crews were afforded great latitude in personal weapons. While the belt-fed M60 was standard kit for aerial observers, captured AK47s and RPDs along with Thompson submachine guns, M16s, and M79 grenade launchers were common as well. The M79 in particular was respected for its unrivalled versatility.
40mm Grenade Launchers in Country The M203 grenade launcher was introduced into service in April of 1969. This underbarrel design subsequently saw use toward the end of the war in Vietnam. The M79 was first adopted in 1960 as part of Project Niblick. A preternaturally simple design, the M79 was little more than a stubby break-open single-shot shotgun on steroids. The barrel was rifled, and the manual arms couldn’t have been simpler. Thumb the barrel release lever right to open the action, drop in a round, close the action, slide off the safety, and squeeze the trigger. American GIs called the weapon the Thumper, Blooper, Bloop Tube, or Big Ed. Their Australian counterparts affectionately knew the piece as the Wombat Gun. The bulky experimental semiauto T148 repeater fed from a harmonica-like magazine but never saw combat. The SEALs used a few pump-action China Lake grenade launchers in action. The single-shot M79, by contrast, was everywhere.
The M203 grenade launcher mounted underneath the barrel of a standard M16A1 rifle and substantially enhanced its capabilities. The 40x46mm round fired from the M79 was specifically designed to cover the dead space between hand grenades and 60mm mortars. The little gun launched these relatively low velocity projectiles in a high arc such that they could drop in vertically behind cover. The effective casualty radius for today’s standard M433 HEDP (High Explosive Dual Purpose) rounds is five meters. The warhead will also punch through two inches of steel armor plate at a 90-degree angle of incidence. This dual purpose round was fielded in 1971. Earlier versions were not so effective against armor, but this was not critical in the jungle climes of Vietnam.
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The war in Vietnam saw the introduction of unprecedented military capabilities. Jets like this F100 Super Sabre would have been unimaginable a decade before. Loach crews suffered some horrible rates of attrition in the down and dirty world where they flew. (Wikipedia photo by Airwolfhound) The weapon’s maximum effective range was 400 meters against area targets and 150 meters against point targets such as doors or windows. The M79 was equipped with a rather complicated adjustable ladder sight and in the hands of an experienced grenadier was remarkably accurate. Like SPC4 Pollard in our little vignette above, experienced Vietnam-era grenadiers with plenty of trigger time were capable of surgical accuracy. M79 grenade launchers were typically issued at the density of one per Infantry fire team or two per squad. 40mm High Explosive rounds travel at around 245 feet per second and have a rotational velocity of 37,000 rpm to the right. This rotation stabilizes the grenade in flight and also provides the centrifugal force needed to activate the spin arming system. Current-issue rounds do not arm themselves until they have travelled about 30 meters out of the tube. Early Vietnam-era 40mm grenades armed at between 14 and 27 meters.
This is a critical feature. Otherwise close range engagements could be as dangerous to the firer as the target. While the M79 was a radically capable weapon for its day, it did have its drawbacks. There were numerous examples of M79 gunners engaging enemy troops inside of that critical arming distance. Under those circumstances the sheer mass of the 40mm projectile could be debilitating but not reliably thus. As a result, the Army developed two different types of close quarters 40mm rounds for use at bad breath ranges.
Australian diggers like these referred to the M79 as the “Wombat Gun.” (public domain). Though undeniably bulky, the pump-action China Lake 40mm grenade launcher was actually fairly successful. It was fielded in very small numbers with U.S. Navy SEALs. (Wikipedia photo by Remigiusz Wilk) The first fired forty-five 10-grain steel flechettes and was colloquially referred to as a beehive round based upon the buzzing sound it made when fired. However, many times at close ranges the flechettes did not have time to orient point first and would strike sideways. In this configuration they were notoriously ineffective. In 1966, the Army adopted the M576 buckshot round. The M576E1 packed twenty 24-grain pellets, while the M576E2 carried twenty-seven. At close ranges these rounds were indeed devastating. However, as the M79 was a single-shot weapon it could be difficult to ensure that the gun was loaded with the right round for the task at hand. The single-shot nature of the M79 as well as the gunner’s limited capacity to pack its heavy ammunition meant that the M79 operator could easily find himself vulnerable at an inopportune time. As a result M79 grenadiers were usually but not always issued an M1911A1 .45ACP pistol as a backup weapon. However, a handgun can seem awfully inadequate in a proper firefight.
The M79 grenade launcher makes for a mean single-shot improvised handgun. This cut-down example was captured from the Viet Cong. (USMC photo) Many M79 grenadiers in Vietnam made use of M16s, CAR15s when available, or even captured AK47s when circumstances allowed as secondary weapons. However, packing two weapons on a patrol is an undeniably cumbersome undertaking. Colt’s response to this firepower conundrum was the Colt CGL4 or XM148 under-barrel grenade launcher. This single shot launcher mounted underneath the barrel of a standard M16 and was the brainchild of one Karl Lewis. Mr. Lewis was a former Dayton, OH, police officer who answered a Colt challenge to develop a piggyback grenade launcher for the then-revolutionary M16 rifle. Lewis took the project from idea to working prototype in a mere 47 days. Karl Lewis was himself a fascinating guy. He developed the interchangeable barrel revolver produced and marketed by Dan Wesson as well as the Browning BLR lever-action rifle. He also helped design the backpack oxygen system used by Apollo astronauts during their walks on the moon.
M79 grenadiers sometimes carried backup weapons such as these when they could be scrounged. The XM148 incorporated an extended trigger assembly that was accessible without removing the firing hand from the pistol grip. This weapon was field tested in Vietnam but found to be susceptible to accidental discharges when jungle foliage caught in the exposed trigger. Though Air Force security personnel continued using the XM148 in limited applications until 1989, the US Army only employed the weapon less than a year. Some enterprising American grunts cut their M79’s down into oversized handguns. Sporting an abbreviated barrel and a pistol grip in lieu of a stock, these improvised weapons were obviously not as accurate as the original hosts but did offer prodigious mid-range firepower. M79 grenade launchers with the barrels and buttstocks cut down remain in use with certain American Special Operations units even today. Navy SEALs affectionately refer to these massive single-shot pistols as “Pirate Guns.”
There’s an Engineering Solution to Every Problem For engagements out to 100 meters there is a fixed battlesight visible when the ladder sight is folded. The M79 stock is a fairly awkward piece of kit. The under barrel M203 successfully rectified the shortcomings of the flawed XM148. The M203 was the only component of the Special Purpose Individual Weapon (SPIW) program of the 1960s to survive into production. Designed by the AAI Corporation and simplified over the XM148, the M203 weighed three pounds unloaded and has matured into a proven combat weapon. The M203 has seen service all over the world. First issued in 1969, the original M203 mounted underneath a standard M16A1 rifle and incorporated a unique black polymer handguard. This handguard mounted a simple flip up leaf sight graduated out to 250 meters that interfaced with the standard front post on the rifle.
The handguard for the M203 was unique to this weapon. The quadrant sight on the carrying handle was the more precise instrument. The simple flip-up ladder sight on the M203 handguard was graduated out to 250 meters. There was also a more precise pivoting quadrant sight affixed to the left aspect of the rifle’s carrying handle. This sight has a flip-out front post and rear peep and is graduated to 400 meters. To operate the M203 you press the left-sided barrel release latch and slide the barrel forward for loading. Slip in a grenade and pull the barrel back smartly to lock it in place. The safety is an ample pivoting tab located inside the trigger guard. Aim the launcher and squeeze. The extractor holds the spent case in place when the barrel is opened such that it typically falls clear of its own accord. The sliding action restricts the length of the rounds that may be fired through the M203, something that is not an issue with the break-open M79.
Most Curious Ammunition The M203 loads from the bottom once the barrel is released to slide forward. What makes the M79 and M203 grenade launchers practical is their remarkably novel ammunition. The physics behind safely launching such heavy projectiles from shoulder-fired guns is indeed fascinating. Like many revolutionary military concepts, we have the Nazis to thank for the inspiration. Toward the end of World War II the Germans were desperate. Allied bombers pummeled German industry, while their corresponding ground armies clawed ever closer on three fronts. Recoilless weapons like the Panzerfaust and Panzerschreck put unprecedented antiarmor capabilities in the hands of the individual Landser. However, rocket launchers and similar recoilless systems consumed vast quantities of propellent. The German answer was the Hoch-und-Niederdruck System. This impressive mouthful of convoluted kraut-speak translates roughly into High-Low Pressure System.
The M79 and M203 served side by side through the latter years of the Vietnam War. Conventional high-velocity antitank cannon consumed relatively modest volumes of propellant but required heavy barrels and breeches. The Panzerfaust and Panzerschreck were far lighter and easier to produce. However, in addition to their gluttonous propellent consumption they also produced a prodigious backblast signature. The German High-Low Pressure System set out to rectify these issues. The best way to appreciate the Hoch-und-Niederdruck System is to visualize a pressure vessel within a pressure vessel. High-pressure gases from the first chamber blow out a thin metal disk to vent into a second, larger chamber contained within the overall metallic shell. The resulting design produces a relatively modest acceleration in comparison to more conventional weapons. Decreased acceleration equals less perceived recoil and larger potential payloads. By using shaped charge technology warheads launched via this means could defeat impressive quantities of armor plate. An operational weapon built around this principle called the Panzerabwehrwerfer 600 was ready for service at the end of the Second World War. However, only 250 examples were ever produced, and none saw action. This same concept was adapted to drive the 40x46mm rounds fired by the M79 and M203. In the case of the American 40x46mm round the two chambers function at 35,000 and 3,000 psi respectively.
Trigger Time ReloadableShells.com is the reason it is worth the time and trouble to buy your own live M203 grenade launcher. M781 training rounds sport a white nylon case and a fairly fragile blue plastic ogive cap. These rounds nicely mimic the trajectory of M433 HEDP rounds but produce a modest splash of orange powder on impact. We called them Cheetos back in the day. Recoil with M781 rounds is modest, perhaps on the order of a 20-gauge shotgun in my subjective estimation. Live M433 rounds push a heavier projectile and seemed to offer a bit more recoil as I recall. However, neither round is terribly unpleasant. The stock on the M79 seems fairly awkward at first brush. The angular nature of the design is intended to orient the line of recoil with the firer’s shoulder. However, this makes for a fairly weird cheek weld. Running the M79 is as simple as your grandad’s single-barrel shotgun. The ladder sight when folded against the barrel features a simple V-shaped battlesight. To fire the M203 you use the host rifle’s magazine as a pistol grip. This maneuver is itself quite awkward as the subsequent length of pull isn’t compatible with any actual human. However, this is a small price to pay to avail oneself of the capability of a standard infantry rifle in addition to the grenade launcher.
Ruminations Reusable rounds from ReloadableShells.com feature the same High-Low Pressure System used in military rounds. The M79 and M203 grenade launchers were called the “Platoon Leader’s Artillery” back in my day. Having reliable, accurate, and effective indirect fires available immediately on demand added a critical new capability to the infantry unit operating in a close quarters jungle environment. Nowadays the 40mm grenade launcher can be found throughout all branches of the US armed forces. Since 2017, the M203 is being actively replaced by the HK M320, but the M79 remains in use for certain specialized applications even today. The innate range and accuracy capabilities of the standalone gun make it a handy tool for addressing IEDs at a safe distance as well as for non-lethal crowd control. Back during the Age of Aquarius, however, the Bloop Tube was an integral part of the Vietnam experience.
Where Do I Get One? My M79 grenade launcher is an exceptionally realistic dummy gun from Sarco. The furniture as well as several other small parts are original GI, while the receiver and barrel are new-made. The barrel is technically rifled, but the ridges track straight rather than in a spiral. The chassis appears to be aluminum. The M79 Sarco replica will pass for the real deal even up close. My world is littered with cool-guy stuff I have accumulated from Sarco over the past several decades. Though I’ve never seen it I presume their warehouse to be like the one in Raiders of the Lost Ark where the Ark of the Covenant resides only cooler. Amongst literally tens of thousands of other things, Sarco also sells a wide selection of dummy and replica weapons. Considering a live version will set you back about five grand when you can find one, at $385 my M79 wall hanger was a steal. Most defense contractors have no interest in selling anything to little guys like us. Lewis Machine and Tool, however, is a gleaming exception. They build and sell legitimately milspec M203 grenade launchers in a wide variety of configurations and would be more than happy to help you hang one on the wall of your man cave. You have several options.
The M781 training round is shown here on the right alongside an M433 HEDP round (top). Despite the fact that you couldn’t obtain genuine high explosive 40mm rounds for love or money, in the eyes of the government a grenade launcher is still an uber-scary Destructive Device (DD) heavily regulated by the National Firearms Act of 1934. That means it must transfer via a licensed DD dealer and entails the same BATF Form 4, fingerprints, and onerous $200 transfer tax as might a machinegun, short-barreled weapon, or sound suppressor. Actual DD dealers are rarer than virtue in Washington, but the BATF will transfer a DD through a conventional NFA or “Class 3” firearms dealer on a case by case basis. As an alternative LMT will also sell you an M203 either without a barrel or with a 37mm barrel that looks like the real deal on the outside. In this configuration the launcher transfers like any other Title 1 firearm through a regular FFL. You can later file a BATF Form 1 to register the gun as a DD and install the live 40mm barrel at home.
