By: Warren Gray

“Always mystify, mislead, and surprise the enemy, if possible.”

— Lieutenant General Thomas J. “Stonewall” Jackson, 1824-1863.

In 1973, the French arms firm of GIAT (Army Industries Group, in English) was founded, and one of their very first products was the lightweight, low-recoil, M621 20mm cannon, currently in use by the French armed forces and 25 more countries. Their most successful application was on the SA341F Gazelle scout helicopter, of which 166 examples were manufactured, and 62 were designated as the SA341F2 Gazelle Canon (“Cannon”), with a fixed, forward-firing, M621 cannon in 20x102mm mounted on the right side of the aircraft, with 100 rounds of ammunition inside the rear cabin.

The rate of fire was selectable at either 300 or 740 rounds per minute (five or 12.3 rounds per second.) This was a very effective, scout helicopter, which remained in active service until 2014, when it was replaced in the close air support role by the EC665 Tigre (“Tiger”) helicopter gunship, with a more-powerful, 30mm anti-tank cannon.

Nexter Systems of Roanne, Loire, France, was founded in 2006, taking over the production of all previous, GIAT products, and adding new products of their own. The venerable, M621 cannon continued to be manufactured in a number of different variants, including the basic cannon itself, the SH 20 (System for Helicopters, 20mm), CP 20 (Cannon, Pintle-mounted, 20mm), THL 20 (Turreted, Helicopter, Light, 20mm), and 15ANarwahl (“Narwhale”) application for naval vessels. The vehicle-mounted, CP 20 model has been renamed the P20 (Pintle-mounted, 20mm) for simplicity.

The M621 has recently been marketed as an upgraded replacement for the Browning M2HB (HB means “heavy barrel”) heavy machine gun on helicopters and ground vehicles, so a direct comparison is certainly in order. The battle-proven M2HB, or newer M2A1, has been around for a very long time, and is the current, world standard for heavy machine guns. It fires the .50 BMG (12.7x99mm) round, typically 750 grains at 2,820 feet per second, out to an effective range of 1,800 meters (1,980 yards, or 1.125 miles.) The weapon itself is 65 inches long, with a 45-inch (almost four feet) barrel, and overall weight is 84 pounds. The rate of fire ranges from 450 to 600 rounds per minute (7.5 to 10 rounds per second.)

Then, there’s the newer, faster-firing, FN M3M model (GAU-21/Ain U.S. service), with a lighter barrel, capable of firing twice as fast, up to 1,200 rpm (20 rps.) This Belgian-designed weapon is in limited service with Canada, Denmark, Germany, Poland, South Korea, Spain, the United Kingdom, and the United States in various capacities, being externally almost identical to the M2HB, except for improvements allowing for a much higher rate of fire.

By comparison, the Nexter M621 revolver cannon, also being offered as a hand-held weapon for helicopter aircrews and ground troops, fires the standard, 20x102mm cannon round, exactly the same ammunition used in the American M61A1 Vulcan cannon on jet fighters, the M197 three-barrel Gatling gun mounted on AH-1Z Viper naval attack helicopters, and the Pontiac M39A2 cannon on F-5E Tiger II fighters, some of which are still in service as aggressor aircraft with the U.S. Navy and Marine Corps.

The M621 weapon is 87 inches long, with a 57.5-inch (4.8-foot) barrel, and it weighs 100 pounds. This makes it almost two feet longer than an M2HB, with a barrel about one foot longer, but weighing only 16 extra pounds, a modest, 19-percent weight increase. Its 20mm ammunition fires at 3,283 fps velocity, out to an effective range of 2,000 meters (2,200 yards, or 1.25 miles) at a fixed rate of 750 rpm (12.5 rps), with a projectile weight of slightly more than double that of the .50 BMG round, and it has a highly-effective muzzle brake to reduce recoil forces, so it’s quite controllable.

So, the Nexter M621 cannon, for only 16 extra pounds, offers 220 yards (or 11-percent) greater effective range than any version of the M2 or M3 machine gun, a higher rate of fire than the ever-popular, M2HB, and at least 30-percent greater “throw weight” of high-explosive projectiles than even the very fast-firing, M3M/GAU-21/A machine gun. And, when compared to the widely-used, M197 helicopter Gatling gun, the M621 is 32 pounds lighter, still has a higher rate of fire (750 rpm vs. 730 rpm), and has significantly greater range.

The M621’s most-recent application has been with the 4th Special Forces Helicopter Regiment (4e RHFS, with the motto of “Nowhere Without Us”), formed in 1997, of the French Army Light Aviation (ALAT) service at Pau, France, near the beautiful, Pyrenees Mountains. This elite unit is officially part of the French Army Special Forces, equipped with six squadrons of helicopters, including 10 AS532UL Cougar utility transports, 12 SA342M Gazelle light scouts (armed with either four HOT anti-tank missiles, or one M134D-H 7.62m Gatling gun on the right side), eight EC725AP Caracal (H225M) army transports, two EC725R2 Caracal air force rescue transports, nine SA330Ba Puma transports (seven army, and two air force, together forming the Joint Helicopter Group, which supports two police, counterterrorist units), and six EC665 Tigre (“Tiger”) HAD attack helicopters, armed with 30mm anti-tank cannon and 68mm rockets.

In addition, the French Air Force’s 1/67 Helicopter Squadron, with the motto of “Fight and Rescue,” also based at Pau, directly supports the Special Forces, and operates nine more EC725R2Caracal transports. By 2025, all 19 French Caracals in army and air force service are expected to be replaced by brand-new, NH90 Caïman (“Cayman”) helicopters.

First of all, it’s noteworthy to mention that 4e RHFS helicopter pilots and aircrews are the most heavily-armed in the world, each equipped with an HK416F short-barrel carbine (reportedly upgraded to the Swiss, folding-stock, B&T APC556 personal-defense weapon, or PDW, last year), an H&K MP7A1 PDW in 4.6mm, and a brand-new, as of last year, Glock-17 Gen. 5 Tactical service pistol.

But more important is the regiment’s use of the hand-fired, M621 cannon in two different applications. Some of the SA330Ba Pumas are in the Puma “Pirate” configuration, with a pintle-mounted (fixed, bulky, 19A floor-mount system) M621 gun firing out the right side of the aircraft. It’s non-retractable, however, so the side door must remain open at all times, clearly identifying these orbiting Pumas as aggressive “gunships,” likely to draw enemy fire.

So, in February 2016, the 4e RHFS and 1/67 Squadron began flying with the newer, SH 20 cannon system, mounting an M621 gun on a swiveling, retracting, hand-fired, pintle mount just inside the right door of 15 of their Cougars and Caracals. This new mounting technique is 334 pounds lighter overall than the older, 19A, “Pirate” system on the Pumas.

The entire, SH 20 gun system weighs 363 pounds empty, or 546 pounds fully loaded with 240 rounds of ammunition. Because it’s fully retractable inside the right door, the SH 20 can be tucked away out of sight inside the helicopter for a non-aggressive appearance until needed, and then rapidly deployed in only 10 seconds. They call this special arrangement the Paquet Surprise (“Surprise Package”), which is especially desirable on the EC725 combat-search-and-rescue (CSAR) choppers, presenting the initial appearance of an innocent, rescue/medical evacuation helicopter until they began drawing hostile fire, and then they can shoot back with speed and total surprise.

The SH 20 system typically fires in eight-round bursts to conserve ammunition, and comes with a special, “Sniper-Shot” function, firing a single,precisely-aimed round, when desired. Its super-accurate, Sagem ODIN (made in Paris. Odin was the powerful, one-eyed king of the Norse gods), quick-detachable, computerized sighting system uses thermal imaging for daytime/nighttime operations, has a lead-computing, illuminated, aiming reticle, a laser rangefinder, and it weighs less than three pounds overall. Brazil has also apparently received and tested at least a few SH 20 gun systems for their EC725s.

In addition, Nexter produces a very sleek, streamlined, NC621 (Nexter Cannon, M621) gun pod, with an M621 cannon and 180 rounds of ammunition. This is available for the AS532AL Cougar helicopter, EC635P2 helicopter (16 made so far for Iraq), Romanian IAR-330L/M, and the A-29A/B Super Tucano light attack aircraft.

The Colombian Air Force operates at least five AC-47T Fantasma (“Ghost”) aerial gunships, actually Basler Turbo BT-67 conversions, with HiTech FLIR sensors for night attacks against roving, FARC guerillas and drug smugglers, each armed with a pair of fixed, side-firing, three-barrel, GAU-19/AGatling guns in .50-caliber. These aircraft were vividly described in my 2008 book, Tequila Moon, about a two-week-long, border confrontation between Colombia and neighboring Venezuela. At least one of these nocturnal gunships, tail number 1658, has been openly photographed mounting a fixed, M621 20mm cannon in place of the rear Gatling gun, adding another element of “surprise” from the night skies for the elusive guerillas on the ground.

There is also a THL 20 turreted version for helicopters, currently employed on the Romanian Air Force’s 35 IAR-330L/M SOCAT (Electro-Optical System for Reconnaissance and Anti-Tank) attack helicopters (Puma variants), with 750 rounds of ammunition loaded. This entire, lightweight, single-barrel system weighs only 361 pounds, and has the same available, “Sniper-Shot” mode as the SH 20 system for high-precision, single shots, when required. It was also selected for India’s new Advanced, Light Helicopter (ALH) and Light, Combat Helicopter (LCH) since 2010. The THL 20 system is lighter, simpler, and faster-firing than the American, M197 helicopter gun.

Finally, there is the new, P20, pintle-mounted, M621 cannon for ground vehicles, recently selected by Poland’s elite, Grom (“Thunder”) counterterrorist force in 2019, with just two orders, followed by seven new orders last year by the German Special Operations Command (KSK) for their light attack vehicles. Nexter also produces a P20 version for ground vehicles in 20x82mm Mauser, but it’s lighter and less powerful, and has an effective range of only 1,500 meters. This may be desirable for some customers, but the harder-hitting, 20x102mm version remains the preferred choice.

In conclusion, Nexter’s versatile, M621 cannon offers a viable, more-powerful, hand-fired alternative to the Browning M2HB, which is especially useful in today’s long-range, desert-warfare environments, and the swiveling, SH 20 version, in particular, may be hidden away as a deadly “Surprise Package” until approaching enemy troops on the ground, and then employed with great, highly-accurate effect only when needed, with much greater range and firepower than a traditional, M2 machine gun. It’s truly an advanced, Special Forces weapon.

Warren Gray is a retired, U.S. Air Force intelligence officer with experience in joint special operations and counterterrorism. He served in Europe and the Middle East, earned Air Force and Navy parachutist wings, and four college degrees, including a Master of Aeronautical Science degree, and was a distinguished graduate of the Air Force Intelligence Operations Specialist Course, and the USAF Combat Targeting School. He is currently a published author and historian. You may visit his web site at: