During World War II, the basic weapons of the U.S. infantryman were the rifle, light machine gun and fragmentation grenades. Hand and rifle grenades were used for short-range area targets. Hand-thrown grenades have a realistic range of 30 to 50 yards. The maximum range of rifle-launched grenades was approximately 100 yards; both were ill-suited for engaging targets with accurate indirect fire. Light mortars were used for ranges from 300 to 900 yards. The same weapons and limitations were fielded during the Korean Conflict by U.S. infantryman.

The Rifle Grenade Launcher

During the late 1950s, the M7A3 grenade launcher adapter was being issued for use on the M1 rifle. After the M14 rifle replaced the M1, the M76 grenade launcher was adopted. For accuracy, the M15 tilting-bar sight, designed to be attached to the M14 rifle’s stock, was issued for use with the M76 launcher. Special “grenade launching cartridges” were used. Rifle grenades could also be launched from the M16 rifle, but no special adapter was needed; grenades could be slipped over the NATO standard 22mm diameter flash suppressor. Disadvantages of launching grenades from rifle barrels included: short range, inaccuracy and heavy recoil that would sometimes break buttstocks.

Clearly, a new weapon was needed, one that could provide accurate direct and indirect fire to fill the gap between the rifle, hand grenades and the light mortar. During the 1950s the United States Ordnance Department began development of a weapon that could fire high explosive munitions, multiple projectile anti-personnel rounds and smoke and illumination rounds.

40mm Ammunition

During the early 1950s the Ballistic Research Laboratories at the Aberdeen Proving Ground developed a 40mm high-explosive, fragmentation projectile. The goal was a range of 400 meters at the relatively low velocity of 250 feet per second, with a recoil force no more than that of a 12-gauge shotgun. The new projectile used a high-low pressure system, which was developed by the German firm of Rheinmetall-Borsig during World War II for their 8cm 8H63 anti-tank gun. The advantage of the high-low system was that a lightweight barrel could be used, reducing the overall weight of the weapon.

The M79 Grenade Launcher

The concept of a lightweight weapon capable of projecting a grenade further than could be thrown by hand and could exceed the range of rifle-launched grenades was coordinated by the Small Arms Development Branch, headed by Colonel Studler. Jack Bird, a deputy to Colonel Studler, took an interest in the project; he built a crude launcher and brought it to the Pentagon to demonstrate. The device was comprised of a short length of tubing with the same inside diameter as a golf ball. To operate the “launcher,” a golf ball would be placed inside the tube and compressed against a spring. The golf ball was secured in place with a nail. Upon removing the nail, the golf ball would be launched. Bird, an avid golfer, suggested the name “Project Niblick” after the number nine iron, a high lofting golf club.

During 1953, the Project Niblick grenade launcher was under development at the Springfield Armory under the guidance of Cy Moore, with Dave Katz, a design engineer. The Picatinny Arsenal provided 40mm practice grenades for firing in the prototype launchers. There were three types of launchers being developed: a crude shoulder fired test fixture, a pistol and a three-shot semiautomatic launcher. The fixture was primarily a means of testing the ammunition to get an idea of the range and accuracy. The weight of the projectile was approximately 5.3 ounces. When launched with a quadrant elevation of 35 degrees, it had a range of 400 meters. Development commenced at the Springfield Armory. Proposed designs were identified by a letter “S” representing the Springfield Armory. Many of the designs never made it any further than the drawing board.

The Infantry Board at Fort Benning stated that they preferred a three-shot grenade launcher. A barrel length of 14 inches evolved as the length to make it unlikely that the gunner could get his fingers in front of the muzzle while firing. The three-shot launcher achieved semiautomatic operation through the use of a clip made up of three side-by-side chambers, each long enough to house a cartridge about 3.5 inches long. The clips would move to the left after firing by a constant force of a negator spring. As each round was fired, a latch detected the launching of the projectile and allowed the clip to move over until stopped by the next projectile, lining up that cartridge with the barrel. Although the basic concept was simple, the mechanism proved to be complex and unreliable. Continued misalignment between the projectile on the bore created gas leakage and a loss of accuracy. Special purpose rounds, such as CS gas or signal flares with a longer overall length, could not be used. The simplest design, designated as the “S-5,” was a single-shot, break-open type weapon. The S-5 evolved into the XM79 in 1959 after the three-shot S-6, T148E1 project was canceled.

After the idea of a multi-shot, semiautomatic launcher was scrapped, it was replaced by a simple, single-shot weapon, patterned after a break-open type shotgun. One launcher was ordered from Dave Mathewson, who operated a local fabrication shop, often used by the Springfield Armory. To keep the weight at a minimum, the weapon featured a hard-coated aluminum barrel. The odd shape of the stock was designed so that the bottom edge would be aligned with the line of recoil; the top or comb is contoured to keep the grenadier’s head upright owing to the line of sight relief when firing at low angles. To reduce the effects of the recoil on the shooter, a rubber recoil pad was fitted to the butt of the stock. The Infantry Board suggested a folding leaf sight mounted on the barrel with a bead front sight just above the muzzle. The XM79 launcher was sent to the Infantry Board in 1956 and was recommended for type classification in 1957.

To load the weapon, the operator simply moves the barrel-locking latch counter-clockwise to open the breech. Moving the release latch automatically puts the weapon into a safe position; opening the breech cocks the weapon. After closing the barrel, the safety must be pushed forward to fire. The weapon is easily field stripped by removing the front sling swivel screw and removing the forend. The barrel can then be disengaged from the fulcrum pin and separated from the receiver group.

The weight of the loaded launcher is 6.45 pounds; overall length is 28.78 inches. The stock and forearm are made of walnut. The rest of the weapon, except for the aluminum barrel, uses steel parts phosphated for corrosion protection. The original contract price for the M79 was $318.00 each. The M79 was issued with a small arms accessory case, which included a bore brush, plastic oil tube, combination tool and cleaning brush. Early carrying cases for the kit were made of canvas, later changed to vinyl.

During testing by the Infantry Board in June 1960, it was recommended that a new rear sight for the M79 launcher be designed and fabricated. The new sight was completed in October 1960. The early ladder-type sight was replaced with an adjustable, single crosspiece-type sight with a correction for azimuth. All launchers produced up to June 1960 had to be retrofitted. Confirmatory tests in December 1960 revealed requirements for additional windage adjustment on the rear sight. The additional sight modification was incorporated in the first production run. R&D continued in order to improve the reliability and function of the weapon. The launcher was considered acceptable by the Continental Army Command (CONARC) and was subsequently type-classified as the Launcher, Grenade, 40mm, M79 on December 15, 1960. By the first quarter of 1961, the new adjustable rear leaf sight was in full production, and several mandatory changes were implemented on the barrel locking lug, trigger spring and front sight.

The heat and humidity being experienced in Vietnam were causing problems with the warping and swelling of the wooden stocks of the M79. As a result, work began on designing a plastic buttstock and foregrip for the weapon. By 1964, a suitable plastic buttstock was available; General Tire was the primary contractor. There were no plastic foregrips adopted.

Although the M79 grenade launcher was designed and developed at the Springfield Armory, the majority were manufactured by civilian companies. Contracts awarded to private industry included: Action Manufacturing Company, Philadelphia, Pennsylvania, Contract DA-11-1199-ORD-736 and Exotic Metal Products, Pasadena, California, Contract DA-11-199-ORD-730. Other contracts were subsequently awarded to the Kanarr Corporation of Kingston, Pennsylvania, and Thompson Ramo Wooldridge (TRW) of Lyndhurst, Ohio. The decision to have private companies manufacture the M79, resulted in a lot of resentment with the civilian employees of the Springfield Armory. Series production ran from 1961 to 1971 with an estimated 350,000 M79 launchers produced.

Despite being replaced by modern grenade launchers, like the M320A1 and the M32A1, the M79 is still being fielded by the U.S. military.

The China Lake Grenade Launcher

Developed for the U.S. Navy SEAL teams was a limited production, pump-action 40mm grenade launcher, fed from an under-barrel tubular three-round magazine. The launcher was fitted with M79 front and rear sights and a shotgun-style stock. There was no official designation other than “The China Lake Grenade Launcher.” The weapon was developed at the Naval Weapons Center, China Lake, California, during 1967-1968.

The XM148 Grenade Launcher

While the adoption of the M79 grenade launcher solved one problem, it created another; it reduced the number of riflemen in a squad, the man carrying the single-shot M79 was usually armed with only a pistol for self-defense. To address the problem, the concept of the rifle-mounted launcher was studied. The 40mm XM148 launcher, first issued in 1967, was designed for mounting under the barrel of an M16 rifle. The weapon was developed by Colt Firearms to allow each rifleman in an infantry squad the ability to launch 40mm grenades, rather than one man equipped with an M79. During field testing in Vietnam, a number of problems were encountered. The XM148 launcher was not considered reliable or safe enough for type classification, and the launchers were pulled from service; most were destroyed.

The M203 Grenade Launcher

After the XM148 grenade launcher was scrapped, the concept of a rifle-mounted launcher was not. The Army initiated a competitive program for a new 40mm rifle-mounted grenade launcher. Designs were submitted by Aircraft Armaments Inc., Ford Aerospace and Communications Corporation and Aerojet Ordnance and Manufacturing Company. During August 1968, the Aircraft Armaments (AAI) design was type-classified as the XM203 grenade launcher. A small lot was manufactured and shipped to Vietnam for field testing. AAI’s XM203 40mm grenade launcher was found to be simple, safe and reliable. After successful testing and evaluation, the Aircraft Armaments design was type-classified as the Launcher, Grenade 40mm, M203 in 1969. Ironically, Aircraft Armaments, who developed the weapon, did not have the capacity to produce the number required by the Army, and a contract to manufacture the M203 was awarded to Colt Firearms. The U.S. M4 Carbine version of the M16 was adopted in 1994. The M203 launcher would not fit on the shorter M4. The M203 GL was modified into the M203A1, which is functionally the same as the M203 but is designed to fit on the M4 and M4A1 carbines. The quick-release M203A2 was designed for M4 carbines with a rail system and with M16A4 rifles that have the M5 adapter rail. Currently, there are at least seven U.S. companies manufacturing the M203 grenade launchers and its variants.

The M320 Grenade Launcher

During 2004, the U.S. Army issued a requirement for a new technically advanced grenade launcher with improved accuracy, ergonomics, safety and function as a stand-alone weapon. Development of the XM320 single-shot launcher, based on the HK AG36, began at the Picatinny Arsenal. The 40mm M320, which can also be attached under the barrel of a host weapon, was adopted in 2016 to replace the M203 under-barrel launcher.

The M32A1 Multi-Shot Grenade Launcher

While fighting in Iraq, the U.S. Marines requested a grenade launcher with a rapid rate of fire. An off-the-shelf, multi-shot revolver type, semiautomatic launcher was submitted by Milkor USA based in Arizona. The weapon was tested in 2006 and was eventually adopted by the U.S. Marine Corps as the M32A1 Multi-shot Grenade Launcher, and by the USSOCOM as the Mk 14 Mod 0.

Working with outside companies such as Honeywell Incorporated, Picatinny came up with a fuze system for the new grenade that was considered a marvel of miniaturization at the time. Even with the small size of the fuze, it was as large as the fragmentation body itself and made up over 50% of the complete projectile. Further studies of the new projectile centered on determining which would be the best way to launch and stabilize it in flight.

Colonel Rene R. Stutler, Chief of Small Arms Research and Development for US Army Ordnance, at his office in the Pentagon had decided that a shoulder fired launcher dedicated to launching the new grenade would be the way the project would go forward. A deputy to Colonel Stutler, Jack Bird, became interested in the grenade launcher project and investigated the idea on his own time.

Taking a piece of pipe that would accept a golf ball, Bird capped off one end and drilled several small holes through the tube’s side. With a spring placed in the tube and a golf ball dropped down over the spring, a stick was used to push the ball down against the pressure of the spring. A nail slipped through one of the holes in the side of the tube held the ball in place on the compressed spring.

Demonstrations of Bird’s “launcher” took place in the central courtyard of the Pentagon. The high arcing trajectory of the golf ball when the cross nail was pulled out demonstrated remarkable accuracy for such a crude device. The high lobbing arc of the ball reminded a number of the onlookers of a nine-iron stroke on a golf course. Jack Bird suggested the program for the new weapon be named after the popular term for a nine-iron at the time, a Niblick. Stutler agreed and Project Niblick was so named.

Once the basic projectile had been established, both a launcher and a means of propelling the grenade were needed. Springfield Armory received funds in June 1952 for its Research and Development Division to conduct a study of various devices to launch the new grenade design. A number of designs were established, built, and tested at Springfield Armory using the various forms of ammunition, now known as the Niblick projectile, coming from Picatinny.

Launchers for the Niblick projectile at Springfield Armory from 1952 into 1955 concentrated on muzzle attachments for the M1 Garand service rifle. These launchers used a blank cartridge to propel a Niblick projectile much like a standard rifle grenade. Designs ranged from a simple tube to a complex 8-round semiautomatic launcher attachment that had a circular magazine holding the projectiles. None of the designs had much advantage over the standard rifle grenade and did not show enough promise for further development.

The Niblick projectile used in most of the muzzle launcher attachments was a drag-stabilized round with an extending skirt that spread out behind the fired projectile. A spin-stabilized Niblick projectile, resembling a fat bullet, was found to have much more promise in terms of accuracy. A cartridge design with a self-contained propellant was needed to further develop the potential of the Niblick projectile.

To fire the very large Niblick projectile from a cartridge case, the standard method of simply filling the case with propellant would not fit the needs of the project. When a standard small arms cartridge is fired, the projectile receives a very violent push from the rapidly burning propellant that gradually lowers in pressure as the projectile moves up the barrel. Using the standard cartridge system with the Niblick projectile would create several recoil problems, eliminating the possibility of a shoulder-launched weapon. Lowering the velocity of the Niblick projectile to allow a shoulder-fired weapon would cause most propellant powders to burn erratically at best, ruining accuracy from round to round, and badly cut back on the effective range of such a system.

During World War II, the Germans had faced a similar question, but for different reasons. The German question was how to build a worthwhile antitank weapon that would be lightweight, use few critical materials, and still have range, accuracy, and lethality. The use of a rocket projectile was ruled out due to an inherent lack of accuracy at long range and a very high consumption of fuel when compared to projectile weight.

A new internal ballistics principle, the “Niederdruck” or high-low pressure system was developed in Germany during WWII and was used by Rheinmetall-Borsig to solve the antitank weapon question. In the high-low pressure system, a relatively small amount of propellant is burned in a high pressure chamber until it reaches a threshold pressure and ruptures a seal. With the seal ruptured, propellant gases bleed through small holes in a metal plate into the low pressure chamber where they bear on the projectile. When fired, pressures in the high pressure chamber reach the 30-40,000 psi range while the low pressure chamber maintains a reasonably steady 3,000 psi. The high pressure chamber allows the propellant to burn completely and efficiently. The low pressure chamber gives the projectile a steady push with the pressure curve having a flat, almost optimal, line.

The steady push of the low pressure portion of the high-low system gives a useful velocity to the projectile but also allows for a more fragile projectile to be used than that of a regular cannon. The low pressure also gives a low recoil impulse but is very consistent for accuracy. The major stress of firing is in the high-pressure chamber so the barrel and resulting support equipment for the weapon can be made much lighter.

The German weapon that fielded the high-low pressure system was the Rheinmetall 8cm Panzerabwehrwerfer 600, or PAW 600. The PAW 600 fired a fin-stabilized, hollow-charge round that would penetrate 5.5 inches (14 cm) of steel, out to an effective range of 600 meters. the smoothbore weapon had a light barrel with only the breech section requiring heavy walls to withstand firing. Set up for action the PAW 600 only weighed some 1,389 pounds (630 kilograms) while a conventional 5-cm Pak 38 cannon weighed 2,205 pounds (1000 kilograms) and only had some 400 meters additional range with much less penetration.

Though considered revolutionary in concept and the only major ballistics advance of the war, the high-low pressure principle was not developed further in the years following World War II. In the 1952-53 time period, Picatinny Arsenal revived the high-low pressure system to propel the Niblick projectile in a self-contained round of ammunition.

The high-low pressure cartridge case was made of aluminum and was unique in its design. The center of the cartridge case was the high pressure chamber, a thick walled extrusion in the center base of the case. Spaced around the side of the high pressure chamber are six precise vent holes. The inside of the high pressure chamber is sealed with a thin brass cup that contains the powder charge and closes off the vent holes. The bottom of the cartridge is closed off with a thick base plug that holds a percussion primer.

When the 330 milligram (5 grain) propellant charge of M9 smokeless powder is ignited by the percussion primer, it builds up a pressure of 35,000 psi while burning. When the 35,000 psi point is reached in the high pressure chamber, the brass seal ruptures and the propellant gases bleed out into the low pressure chamber where they are reduced to a pressure of 3,000 psi. The 3,000 psi pressure moves the projectile up the barrel at a relatively slow rate, maintaining close to full pressure throughout a 14-inch barrel length. The Niblick projectile left a 14-inch barrel with a muzzle velocity of 250 feet per second and a right-hand spin of 3,700 rpm due to the rifled barrel.

The self-contained Niblick round kept a relatively low bore pressure in the launchers when compared to standard ammunition. The only point of high pressure stress when firing the round was taken up by the high-pressure chamber itself. These facts allowed the barrels of the various Project Niblick launchers to be made of aluminum. The low muzzle velocity also prevented any of the launchers from having excessive recoil even though a very large and heavy projectile was being launched for a hand-held weapon.

A number of launchers for Project Niblick were produced at Springfield Armory in 1953 under the direction of the project director, Cyril Moore. Two specific designs of launchers for the Niblick round showed considerable promise. One device was a simple shotgun-like fixture for determining ballistic data for the complete Niblick round. The other launcher was designed to fire six rounds semiautomatically. This was the first of the Project Niblick weapons that was a dedicated, shoulder-fired system. With a large rotating cylinder, the device acted much like a shoulder-fired revolver. Though the idea of semiautomatic fire held promise, the first device was found to be unsuitable for military use.

In the 1954-55 time period, the focus at Springfield Armory was on utilizing the complete Niblick round, though there was still some experimentation with the earlier types of projectiles. At this time, the S-3 launcher, a single-shot, break open, shoulder fired device with a rifled barrel was produced. This device greatly resembled the Federal Laboratories tear gas gun that was popular with police departments at the time but with a more complex sight and a forward hand grip.

A more complicated launcher that had semiautomatic capability was developed and under study by 1955. Identified as the S-6 strip-type shotgun, this was the first weapon to use a semiautomatic capability built into a conventional shotgun format. The S-6 used a harmonica-like strip of three Niblick rounds, each held in its own firing chamber, and feeding through the side of the receiver to give a semiautomatic fire capability. As each round was fired, a spring would drive the strip clip through the receiver until it indexed on the next loaded chamber. This form of launcher met with high approval in the conferences between Springfield Armory and Army Ordnance personnel and effort was put into refining the design.

A second generation semiautomatic S-6 launcher was available within a few months of the first model being accepted for development. Shortcomings from the first S-6 were eliminated in the second generation design. Further work was needed to meet the military needs of such a weapon system and study continued on the design. Other launchers were examined, including large flare-gun like pistols, to use the Niblick round, but none of the designs met with much success.

Later in 1955, the experimental Project Niblick weapons were due to be tested by the Army Infantry Board. Lieutenant Colonel Roy E. Rayle, the Small Arms R&D Chief at Springfield Armory, suggested further development go into another single shot launcher like the earlier S-3 design. Instead of developing a new design, Rayle suggested an already existing pattern, such as the Stevens Model 220 hammerless shotgun with a top-mounted safety and release lever, be modified to fire the Niblick round. The advantages of such a design would be the simplicity of operation and ease of training to recruits.

Lieutenant Colonel Rayle’s suggestion was followed and a second launcher was developed along the lines of the S-3, this one identified as the S-5 shotgun. The S-5 was the first attempt to build a Niblick launcher that followed the lines of a conventional, single-shot, sporting shotgun. The lines of the S-5 remained simple and the mechanism straightforward. Further development continued on the design especially on the shoulder stock and sight configurations. An immediate drawback to the S-5 that limited its appeal to the Army personnel was that the system was single-shot only.

During testing, the S-6 repeating grenade launcher was found to have problems with accuracy and was considered awkward to handle and operate. These problems were quickly traced to the harmonica magazine. A lack of a positive seal between the mouth of the magazine and the rear of the barrel caused propellant gases to slip though the gap. This caused irregular muzzle velocity in the S-6 weapon and greatly limited the firing accuracy of the system. The much simpler S-5 launcher was favored by the Infantry Board testers. A decision was made to try and correct the problems with the S-6 launcher in order to retain the semiautomatic capability while retaining the S-5 design in reserve.

By 1958, the S-6 design had evolved into the T148E1 and T148E2 launchers. The T148E2 design was more complicated than the E1 as it incorporated a break-open design to help seal off the barrel/magazine gap. The greater number of components in the T148E2 design eliminated it from further development in favor of the simpler T148E1 pattern. A limited pilot-line production of 200 T148E1 launchers was conducted between 1 January and 30 June 1958 to supply a number of the weapons for field testing and further evaluation. The gas bleed-off at the chamber/barrel gap still caused an unacceptable loss of accuracy and the T148 project was terminated after 1 July 1960.

A conference of Army and Springfield Armory personnel decided the S-5 design, now known as the XM79, should be reactivated. US Army Infantry Board testing determined that a new sighting system should be designed and a few shortcomings of the XM79 be corrected before acceptance. The new sight design was ready by October 1959 and all XM79 launchers produced up to that point refitted with the correction. On 15 December, 1960, the M79 was officially type-classified and adopted by the US Army. Further production difficulties in producing the complicated rear sight limited weapon availability for some years after adoption.

By 1965, the M79 grenade launcher was in full production and available for issue to all of the services.

Initially with the Teams, the primary round of ammunition used with the M79 was the M406 high explosive round. The large, heavy, projectile of any of the 40 mm rounds could be easily seen by the gunner as they lobbed through the air. Being able to actually see the projectile in flight was a bit disconcerting at first, as the projectile’s large size and low muzzle velocity made it appear the wobble through the air without the ability to hit anything accurately. Confidence with the new weapon came with training. SEALs during pre-deployment training would practice extensively with their weapons, M79s among them. Even with its high, arcing trajectory and apparently slow travel, grenadiers soon learned that the 40mm grenade could be almost amazingly accurate.

Experience with the weapon is what developed skill in an M79 grenadier, and the Teams made certain some of that experience was with their men right from the start. As part of their combat preparation, SEALs would spend hours on the range practicing with their chosen weapons. A skilled M79 grenadier could often drop a grenade right onto a target that was 150 meters away by simply pointing his weapon and looking along the barrel. This kind of shooting was considered instinctive, very quick, and didn’t employ the fairly complex rear sight of the M79 at all. When using the sights and aimed carefully, the accuracy of the M79 was such that a good operator could consistently drop grenades into a garbage can at 150 meters.

Working against the accuracy and effectiveness of the M79 was the fact that it was a dedicated, single-shot weapon. Any SEAL who carried an M79 was very limited in what he could do with the weapon during a close-in encounter of less than 15 meters. The minimum arming range of the grenade, combined with its bursting radius, made the round ineffective and dangerous when used close-in during a sudden eyeball-to-eyeball encounter with the enemy.

becomes a non-issue and the SEAL would open fire with whatever he had in his hands. When a 40mm grenade struck a target in an unarmed condition, it would still act as a very large bullet. A dead VC struck with an unexploded 40mm grenade might become a problem for explosive ordnance disposal, but the SEAL would still be around to report the incident.

Prior to the SEALs sending direct action platoons to Vietnam, Marine and Army units had been in combat in Southeast Asia and had reported the drawbacks of the M79 for close-in combat. New rounds were developed for the M79 and sent over to Vietnam for combat testing. The first of the close-combat rounds for the M79 was a flechette round loaded with 45 finned steel flechettes carried in a plastic sabot. The 10-grain flechettes resembled sharp finishing nails with fins stamped into the head and were effective immediately after leaving the muzzle of the launcher.

When fired, the plastic sabot holding the bundle of fletchettes would break away soon after the projectile left the muzzle of the weapon and the flechettes themselves would spread into a widening pattern. But, as with most of the small-arms flechette loads used in Vietnam, the little finned needles were not stable at the muzzle of the weapon and usually weren’t flying straight and point first until they had traveled about 15 to 30 meters through the air. Close-in, as many as half the flechettes would hit a target sideways or backwards as point on, severely limiting the effectiveness of the round.

Two types of buckshot round were developed for the M79 in the 1965-66 time period to replace the fletchette load. The XM576E1 and XM576E2 rounds were both loaded with #4 (0.24 inch) hardened buckshot. The two cartridges differed in the plastic sabots that were used to launch the buckshot payloads. These rounds began arriving in Vietnam during the SEAL’s first deployments but were not widely available.

Higher command thought the new rounds for the M79 may have too short a range and be ineffective because of that. SEALs in the field did not hold such an opinion and thought highly of the new ammunition. The XM576E1 round was not as effective as the E2 design, which was later adopted as the M576 Multiple-projectile round, but both rounds turned the M79 into a very large shotgun. One of the reasons shotguns were so popular among the SEALs was that the buckshot loads had a great deal of stopping power, especially at close range. Flechette loads, though lethal, didn’t transfer their energy into the target efficiently and never had the knock-down power of buckshot.

With the new multiple-projectile rounds, the M79 became effective at close range. But the basic weapon was still a single-shot design. Once the M79 had fired its round, the grenadier was out of the action until he had reloaded. In the sudden combat environment of the SEALs, this situation could easily lead to men being killed because they had an empty weapon. Without there being any way to speed up the reloading of an M79, SEAL grenadiers simply took to carrying more than one weapon. In the US Army and Marine Corps, grenadiers were normally armed with an M1911A1 pistol in addition to their M79, SEALs preferred considerably more firepower.

Ammunition counts were always high when SEALs went into combat. The larger the SEAL, the more ammunition he would carry. Though the individual round count for 40mm ammunition might be low, the rounds themselves were fairly large and each weighed about half a pound. Depending on the mission, a SEAL grenadier might carry a very heavy load of 40mm grenades along with his additional equipment.

Development of new ammunition types was considered a primary means of increasing the usefulness of the M79 in general. Literally dozens of new rounds were experimented with during the course of the Vietnam war. Some of the rounds, such as the XM576E2, eventually reached standardization, others never went to combat and were only produced in small number for testing. From the very earliest operations of the SEALs in Vietnam, new types of 40mm ammunition was desired and obtained whenever possible.

•Excerpt from SEAL Team Two, 2nd Platoon’s Vietnam operations, 30 January to 30 May 1967

Weapons and Equipment

6. If flare rounds and canister rounds were available for the M-79, the weapon’s versatility would be increased tremendously.

7. Mk 8 Very pistol rounds can be fired from the M-79.

The primary mark against the M79 was still the fact that the weapon was single shot. That had been a concern back in the mid-1950s when the design was first considered. The relatively low recoil of the 40mm ammunition family, combined with its low firing pressure, allowed another approach to solving the single-shot problem.

In September, 1964, Karl Lewis and Robert E. Roy applied for a patent on a grenade launcher attachment they had designed for Colt Firearms. By October 1966, the patent was granted but Colt had already been marketing the new weapon since 1965 as the CGL-4 (Colt Grenade Launcher), part of their CAR-15 weapons system. The CGL-4 could be mounted underneath the barrel of an AR-15 (M16E1) and operated independently of the rifle. The CGL-4 had its own controls and sighting system and used the rifle solely as a support and to supply a buttstock for firing.

To mount the CGL-4 on a rifle, the standard handguards would be removed and the CGL-4 clamped in place on the barrel. A new handguard would be placed on the barrel of the rifle to protect the operator and the grenade launcher would be ready for use. As long as there was sufficient barrel length, a CGL-4 could be mounted on any of the AR-15/M16 weapons including the short CAR-15.

A small pistol grip underneath the CGL-4 allowed an operator to unlock and slide the 40mm barrel forward, automatically extracting and ejecting any fired casing that might be in the chamber. Slipping a loaded round into the barrel and using the pistol grip to pull the barrel shut and lock it in place was all that was necessary to load the CGL-4.

A large knob on the rear of the CGL-4 receiver would be drawn back with the fingers to cock the weapon. A trigger bar extended down the right side of the supporting rifle and ended just in front of the trigger guard. Extending the end of the trigger and rotating it in place put the trigger of the CGL-4 just below the trigger of the supporting rifle. The dual trigger allowed the operator to fire either the M16 or the CGL-4 by simply moving his finger to the proper trigger.

The US Army found the CGL-4 a possible “off-the-shelf” answer to the limited firepower of the M79 in 1966. With minor modifications, the CGL-4 went into limited production in November 1966 as the XM148. Both the US Army units in Vietnam and the Navy SEALs received the new launchers in early 1967. Now for the first time, a weapon was available that had both a point target effect (the rifle) and an area target effect (the grenade launcher). The concept was new and reactions from the men in the field were carefully examined. For the SEALs, this reaction was enthusiastic.

Though the XM148 was well received by the SEALs, they were not blind to the drawbacks of the weapon. The XM148 was a lot more fragile than the simple M79, and had a great deal more parts to get out of order. There was no guard for the XM148’s trigger bar that extended down the right side of the carrying rifle. Any piece of brush, equipment, or even a finger that got between the trigger bar and the receiver of the rifle would push the bar out and jam the XM148 so that it couldn’t be cocked. In addition, the bare trigger bar could hang up on some material during a crawl and fire the XM148 if the weapon was cocked and the safety off. It was this drawback that caused the recommendation to go out that the XM148 could be carried with a round in the chamber, but that the weapon should not be cocked until just before use.

The final Army report on the XM148 was written in May, 1967. A number of the Army users liked the XM148 but the weapon was found to be too fragile and unsafe for general issue. The reporting team concluded that “the XM-148 in its present configuration is unsatisfactory for further operational use in Vietnam.” Recommendations were that the XM148 be removed from service until another design was available. By the fall of 1967, all of the Army’s XM148s had been turned in. The SEALs found the effectiveness of the weapon offset the bad parts of the design and retained theirs until the end of the Team’s involvement in Vietnam.

The XM148 had some unusual aspects to its action that were discovered and used by many of its operators. The sear lever of the XM148 was exposed at the rear of the receiver to the weapon. Operators in both the Army and the SEAL Teams found that you could fire the cocked launcher by pressing on the upper part of the sear lever with the thumb of the left hand without letting go of the pistol grip to the M16 with the right hand. Though not officially recommended, gunners found they could move through the undergrowth with one finger on the trigger of the rifle and the thumb of the other hand on the sear bar of the grenade launcher. Either weapon could be fired immediately without changing hands.

The Teams liked the XM148, but still wanted the firepower of the grenade launcher system increased. SEAL Team One examined at least one of the Springfield Armory produced T148E1 repeating grenade launchers for possible adoption early during their Vietnam war commitment.

•SEAL TEAM ONE – COMMAND AND CONTROL HISTORY – 1967

NWC ORD TASKS…. A listing of special procurement actions completed is summarized below:
[item 9] 40 M Grenade Launcher T148[E]1

It has not been reported that the T148E1 launcher examined by SEAL Team One was ever tested in combat in Vietnam. Though an interesting approach to the semiautomatic grenade launcher problem, the action of the T148E1 was too open and vulnerable to dirt to operate well in the jungle/mud environment of Vietnam. The sliding harmonica magazine has several open chambers that would pick up dirt and debris like scoops as the weapon was moved through the jungle. The sliding operation of the magazine, along with its coil-type driving spring, would also be easily put out of action from dirt and debris. Lastly, the accuracy problem from the shot-to-shot difference in muzzle velocity had never been completely corrected and varied not only from weapon to weapon in the T148E1, but also from magazine to magazine in the same launcher.

The Navy Special Warfare Groups (Pacific and Atlantic), which included the SEAL Teams and UDTs, had been recognized as having unique problems in the field of weapons and equipment by the Navy command. The Special Operations Branch of the Naval Weapons Center at China Lake, California, was structured to address the equipment needs of the SEALs and UDTs on a very rapid basis. Non-standard ordnance and hardware required by the Teams would be acquired by China Lake, modified if necessary, and shipped out to the users as quickly as possible. When a necessary item was not available in any form “off-the-shelf”, China Lake was set up to design, develop, and put into limited production, such items as necessary. In three years of operations during the Vietnam War, China Lake put out some 375 items on a quick-reaction basis for the Teams.

China Lake looked into the question of increasing the firepower of the 40mm grenade launcher. Taking the direct approach, the China Lake engineers applied the pump-action operating principles from civilian sporting shotguns to the problem. Production of a tool-room prototype weapon was completed rapidly and the design was ready for testing and examination. The general design was considered acceptable and a small production quantity was produced at the China Lake facilities. Development of the pump-action grenade launcher was so rapid that it reportedly took longer to make a set of production drawings from the tool-room gun than it did to produce the first weapon.

The China Lake pump-action grenade launcher resembled a very large, short-barreled shotgun and retained the same range and accuracy of the M79. Considered one of the most significant small arms produced as part of the Naval Special Warfare Projects at China Lake, the pump-action grenade launcher was ready to be issued to the SEAL Teams for combat in Vietnam by mid-1968.

•SEAL TEAM ONE – COMMAND AND CONTROL HISTORIES – 1968,

Enclosure 3, SPECIAL TOPICS, (a) Performance of Weapons Systems

The 40MM grenade pump weapon has proven to be a good weapon and is being used by SEAL detachments in Vietnam…

Though a fairly large weapon, the 40mm pump-action grenade launcher was very well received by some of the SEALs in the Teams. Reports on the actual number of China Lake pump-action grenade launchers made are difficult to confirm. Between 20 and 30 weapons were put into SEAL hands during the Vietnam War with only one or two additional launchers going to the Marine Corps Force Recon units and Army 5th Special Forces Group. A receiver with the serial number “50” has been located but it was found in a stripped condition and may never have been assembled as a complete weapon.

The pump-action grenade launcher was one of the most successful of the shoulder-fired 40mm designs, but it was not the only one to come out of China Lake. During the calendar year 1966-1967, NWC China Lake designed and built several prototypes of a 3-barrel 40mm grenade launcher. Instead of developing a multi-shot grenade launcher that would be a dedicated weapon such as the M79, China Lake went with a much smaller design that could be mounted underneath an M16 in the same manner as an XM148. To minimize the size of the 40mm repeater, each round was given its own barrel.

The double-action firing mechanism has a trigger that fits underneath the trigger guard of the M16 in a sliding mount. The trigger bar extends along the right side of the M16 receiver in the same manner as the XM148 but with the trigger in a firm mount, there is much less probability of jamming up the bar with brush as could happen with the XM148. The fairly complex firing mechanism cocks, advances the hammer in a circular motion to the next barrel, and fires the round when the trigger is pulled once. This allows the operator to fire up to three grenades as fast as he can pull the trigger.

To keep the 3-barrel compact enough to fit underneath a CAR-15, the barrels are only six inches long. The short barrels are long enough for the fired grenade to pick up enough velocity and spin to arm and stabilize in flight. But the short barrels also reduced the effective range of the 3-barrel at least 15% less than that of an M79. A large housing covered the rear of the 3-barrel to protect the firing mechanism with the entire package ending up being about 4.25 inches wide.

At least one of the two or three prototype 3-barrel 40mm launchers was sent to the Marines to be tested by the Force Recon units in Vietnam. All of the other examples were sent on to the SEAL Teams for field testing. One grenadier from SEAL Team One carried an M16 with the 3-barrel launcher to test and evaluate it under combat conditions. The one operation where the SEAL carried the weapon took place on 13 April 1968 and was the only operation where this individual carried the weapon. To put it simply, the SEAL reported that the weapon was heavy, unbalanced the rifle badly, and simply did not work.

The complex firing mechanism of the 3-barrel could not stand up to the dirt and mud of the Vietnam environment. When the trigger was pulled, the weapon had as good a chance of not firing as of going off. The wide open muzzle of the three barrels were also very hard to keep free of debris when crawling through the jungle. The weapon was not adopted by the Teams and only the few prototypes were ever made.

The failure of the Colt and China Lake underbarrel grenade launcher attachments did not eliminate the idea for combining the point fire of a rifle with the area effect of the 40mm grenade launcher. The US Army put out the information to the firearms industry that they were interested in another underbarrel grenade launcher design. Seventeen different firms were spoken to during a conference on 18 July, 1967. Seven of the contacted firms reported a serious interest in the project.

AAI (Aircraft Armaments Inc.) had experience in developing a number of underbarrel grenade launchers as part of the Special Purpose Individual Weapon (SPIW) Program. AAI already had an idea in the mockup stage for a new grenade launcher in July of 1967 but the Army felt their estimated production schedules may not be possible to meet. By September, three companies, AAI, Philco-Ford’s Aeronutronics Division, and Aero Jet General had all received contracts to develop grenade launchers as part of the Army’s new Grenade Launcher Attachment Development (GLAD) Program.

The Aero-Jet design for a delayed blowback operated grenade launcher was declined by the Army and dropped from the competition. Twenty each of the Philco-Ford and AAI designs were set for testing on 1 May 1968. “Unanimously selected based on superior performance and predicted lower cost in production,” the AAI design was awarded a contract for further development on 2 August 1968. By early November of that same year, the AAI design was officially identified as the XM203 40mm Grenade Launcher.

A contract for 500 XM203 grenade launchers was awarded almost immediately after AAI received the designation for their design. By December, the XM203 launcher itself was considered complete by the US Army, though further work had to go forward on a selection of sight designs. This work was quickly completed and the construction of the first 600 XM203’s finished by AAI. In April 1969, 500 XM203 grenade launchers were sent to Army units in Southeast Asia for a 3-month combat evaluation.

The XM203 grenade launcher is a single-shot, manually operated, pump-action grenade launcher intended to be installed underneath the barrel of an M16 rifle. The barrel of the XM203 does not extend much past the front sight assembly on a standard M16 and so can be mounted underneath the barrel of any of the CAR-15/XM177 versions of the same weapon. A flip-up ladder-type leaf sight in attached to the handguard of the M16 so that the normal front sight of the rifle can be used to aim the grenade launcher. In addition, a complex quadrant sight is attached to the carrying handle of the mounting weapon for more precise long-range use of the grenade launcher.

To load the XM203, the unlocking lever above the barrel on the left side of the weapon is pressed in with the thumb and the barrel slid forward. Any empty cartridge case will be automatically ejected and the operator can load a single round of any of the standard 40mm grenades. Pulling the barrel shut locks the breech and completes loading the grenade launcher. There is no pistol grip for the XM203, the operator grabs the magazine of the M16 with his firing hand and pulls the trigger of the grenade launcher just in front of the magazine well.

The safety of the M203 is a curved metal flap that will extend in front of the trigger when on. The operator can easily move the safety forward with his trigger finger when ready to fire. One drawback of the M203 is that the spring metal trigger guard, which locks against the front of the magazine well of the carrying weapon, can be slipped up excessively during assembly and block the trigger so that the weapon cannot be fired. This is a minor, but common, error that can be corrected quickly by the operator.

The XM203 was well received by all of the units who used it. AAI was unable to build production quantities of the XM203 and Colt received the contract to produce the accepted M203 grenade launcher for all of the US services. By 1986 Colt had manufactured over 250,000 M203 grenade launchers. The SEALs began receiving the M203 grenade launcher by 1970 and have continued using the weapon to this day. After the end of the Teams involvement in Vietnam, the XM148 grenade launcher was phased out of use and replaced with the M203. In the Teams the M203 was usually mounted underneath the barrel of an XM177E2, replaced today with the M4A1 carbine.

•SEAL TEAM TWO COMMAND AND CONTROL HISTORY, 1970

Enclosure 1, VI. NEW EQUIPMENT, pg 12

1. (U) During the year, SEAL Team TWO received ten new XM203 grenade launcher attachments for the M16 rifle. The XM203 replaces the XM148.

In some combat situations today, whole 16-man SEAL platoons, less automatic weapons men and snipers, have been armed with M4/M203 grenade launchers. The flexibility of the weapon, combined with its firepower, has made it one of the most successful weapons developments to come out of the Vietnam war.

Due to its greater inherent accuracy, the M79 is still found in the SEAL Teams today. The M79 is issued primarily for backup use by a SEAL who is armed with another primary weapon that cannot accept an M203 launcher.

Instead of developing a fully-automatic grenade launcher, the Honeywell engineers suggested that a mechanical repeater be done instead. Instead of trying to adapt a standard automatic weapons design to the characteristics of the 40mm grenade, a hand-cranked repeater would be much simpler to produce in a very short time. The idea was moved forward as an in-house development with no government contract pending. By 1965, the first launcher was ready for demonstration.

In place of a normal chamber, the new launcher had two rotors the length of the cartridge case. Each rotor had six semicircular grooves cut in its length, each half the circumference of a 40mm round. The two rotors were geared together so that a 40mm round would be held in a complete chamber made up from the two rotor halves. Since the chamber formed around the cartridge, the normal functions of chambering and extracting didn’t have to happen. This gave the Honeywell a very simple operating system with relatively few parts.

The two rotors were driven by a side-mounted crank handle, much the same as an old Gatling gun. The rotors were locked into place by a cam driven rod as the firing pin was cocked and dropped by another cam. Rotating the crank handle fired the Honeywell when the handle was at the top or bottom of a rotation, launching two grenades for each full revolution. Depending on how fast the operator turned the handle, the Honeywell would fire at rates of 1 to 250 rounds per minute.

Ammunition for the Honeywell was placed in a plastic belt, spaced out at proper intervals. The initial belts were nothing more than fiberglass-reinforced sticky tape, with the rounds stuck between two lengths of the tape. Spacing of the rounds in the tape belt was done with two tape clinching wheels (large gears) in a special loading machine. The tape belt gave a great deal of trouble when the weapon was introduced and were quickly replaced by a stronger system.

The new belts for the Honeywell were made of Mylar-backed Dacron fabric with pockets between heat-sealed sections of the belt. The fabric belts were supplied in 24 or 48 round lengths and could be reloaded about five times before they wouldn’t hold the 40mm round firmly enough. Old fabric belts sometimes were seen in Vietnamese and other hands being used as 40mm bandoleers.

The Honeywell was examined by the Navy in 1965 for possible adoption as a small boat weapon. Testing proved the system and the Honeywell received the nomenclature assignment of Gun, Rapid Fire, 40mm Mark 18 Mod 0 on 10 December 1965. Between 1965 and 1968, when production ceased, about 1,200 Mk 18 launchers were produced, almost all production going to the US Navy.

Though the Mk 18 could produce a good deal of firepower, it was considered a temporary, stopgap weapon until a self-powered design could be developed. There wasn’t a secure seal between the cartridge case and the barrel so propellant gases leaked out, limiting the muzzle velocity. Accuracy suffered as a result. Volume of fire was considered the Mark 18’s main advantage.

The Mk 18 was able to fire an entire belt of 48 rounds as fast as a man could turn the handle. By carefully sweeping the weapon back and forth, starting at the longest range (400 meters) and working back, a football-field sized area could be covered with one 48-round belt of ammunition. Properly done, all of the grenades would impact at roughly the same time due to the high lobbing arc of the 40mm grenade.

•SEAL TEAM ONE – COMMAND AND CONTROL HISTORY – 1967

The performance of the MK 18 Honeywell has proved unreliable. The quality control must have been lacking since the engineering of certain vital parts is sub-standard. At the present time the MK 18 is unsuitable for SEAL Team operations.

Further testing and development of the Mk 18 continued on a limited basis. The introduction of the Dacron fabric belts helped eliminate many of the earlier complaints about the weapon.

The SEALs used the Mk 18 primarily from PBRs and other river boats. The Mk 18 could be fitted to the standard .30 caliber machine gun tripod for ground use, but the weapon was difficult to operate in such a manner. The SEALs only used the ground mount tripod when introducing trainees to the Mk 18 for familiarization.

Probably one of the most unusual mounts for the Mk 18 was also its most common one. The Mark 46 Mod 0 gun mount would cradle an M2 HB .50 caliber machine gun on a tall, tripod-like Mk 16 stand. This mount was often seen at the stern of the Mk II PBRs as they patrolled the rivers of Southeast Asia. The Mk 46 mount would also hold a Mk 18, or later Mk 20, grenade launcher above the rear of the .50 caliber. A gunner could switch from the point fire of the .50 caliber to the area fire of the grenade launcher by simply changing which grips he held.

THE MARK 20

The Mk 18 grenade launcher was still a manually operated weapon and considered not completely satisfactory by the US Navy. In August 1966, the naval Ordnance Station in Louisville, Kentucky was ordered to develop a 40mm machine gun, capable of semi automatic and full automatic fire, as quickly as possible. Henry Watson, the Engineer in Charge, Colonel George Chinn, and William Schnatter attacked the problem of the new design vigorously. By May, 1967, only nine months later, the first three weapons of the new design were ready for testing.

On August 6, 1968, the new grenade launcher received the nomenclature assignment of Gun, Machine, 40MM (Grenade) Mark 20 Mod 0. The item description on the assignment request read;

This is a lightweight, automatic, low-velocity, reciprocating barrel-operated 40mm weapon. It is 31” long, 9” wide and 9” high and fires M381, M382, M387, M406, or M407 40mm grenades belted with the M16 metallic links, at a rate of 200 -250 rounds per minute in either full or semi-automatic modes. It was designed for pedestal mounting, however, because of its recoilless action, it is adaptable for multiple mounting systems such as tripods and bipods.

The Mk 20 has a sheet metal receiver over a framework that holds the operating parts, A set of twin spade grips are at the rear of the weapon with a push-button trigger that can be depressed with the thumb of the right hand. A sliding safety switch is to the left of the trigger button. The cycling of the weapon is so slow that the trigger button is just quickly released for semi-automatic fire.

The operation of the Mk 20 is a unique combination of blow-forward and recoil. To cock the weapon prior to firing or loading, the cocking knob at the top rear of the receiver is pushed forward. Pushing the cocking handle forward moves the barrel forward, extending it out from the front of the receiver, where it locks into place. When the trigger is pushed, the barrel slides back over the 40mm round in the feed tray. The rifling in the barrel presses back on the rotating band of the grenade, driving the round back onto the firing pin which sets off the propellant charge.

The force of the grenade going down the barrel drives the barrel forward against the barrel spring. A lug on the barrel engages a ratchet cam underneath the barrel that rotates the feed mechanism to move the ammunition belt forward one round. The bolt also recoils from the force of firing, moving against several springs. As the bolt reaches the end of its travel, it moves forward under the power of the bolt springs and a mechanical connections helps the barrel rotate the ratchet cam.

The balance of forces in firing the Mk 20 results in the weapon having very little felt recoil. Though designed to be fired from mounts, the Mk 20 can be hand-held and fired for short bursts with no real difficulty. Accepted by the Navy and in limited production by 1970, the Mk 20 replaced the Mk 18 grenade launchers still in service. The Mk 20 could be mounted on any standard pintle mount or piggyback above a .50 caliber machine gun on the Mk 46 mount. Some 1080 Mk 20 launchers were reported as being made before production was suspended in April 1971.