This article will focus on crew-served gunnery. The concept of the door gunner originated during the United States' involvement during the Vietnam War between 1965 and 1975, when helicopters were first used to support combat in large numbers. For the majority of that war, the principal weapon of the door gunner was a medium Machine Gun (MG), initially the 7.62mm M1919A4, a variant of the M1919 Browning machine gun produced since 1919 by numerous manufacturers, and soon thereafter the US Ordnance/General Dynamics M60 7.62mm MG became the standard helicopter door armament. The mission for door gunners has largely remained the same throughout the years, but with more emphasis on airspace surveillance; and passenger and cargo support. In the US Army today, door gunners double-up as Sikorsky UH-60 medium-lift utility helicopter family or Boeing CH-47D/F heavy-lift helicopter crew chiefs.
The primary weapon for the US Army helicopter door gunner is FN Herstal's M240H machine gun. The M240H is a modified version of the M240B, and is a fully-automatic weapon that fires 7.62mm ammunition. UH-60 family aircraft are mounted with two door gun positions; and CH-47D/F aircraft can be mounted with three door gunner positions, the third mount being on the aft ramp. For night operations, door gunners use night vision goggles with gun-mounted lasers for more accurate aiming. During combat, door gunners have the ability to transform the M240H into a ground weapon in the event that the crew needs to egress following an incident requiring the crew to land outside a secure area. In addition to the M240H, the US Army uses the US Ordnance/General Dynamics M3-series 12.7mm machine gun, and the Dillon Aero M134D 7.62mm Minigun on its Special Operations helicopters.
Today's United States Marine Corps (USMC) utilises this capability on the CH-53E Super Stallion heavy-lift helicopters and the UH-lY Venom light utility helicopter, and will soon introduce the capability on the new CH-53K King Stallion. The USMC employs the Defensive Armament Subsystem (DAS) which serves as a platform interface for which crew-served weapons, external tanks and rocket pods are fitted to the UH-1Y. Adapters to the DAS facilitate different types of USMC crew-served guns, of which the most common types in service today are the FN Herstal GAU-21A 12.7mm machine gun, the GAU-17 (Dillon Aero M134) Minigun, and the FN Herstal M-240H machine gun.
Major Scott Roland is a USMC aviation ordnance officer and is currently the deputy programme manager for aircraft gun systems at the US Navy's Naval Air Systems command and Patuxent River, Maryland. He said, "When I first came into the Marine Corps we were using the old Vietnam-era M60 machine gun (see above), but somewhere around 2000 we replaced that with the M240. We also used the Dillon Aero GAU-2B 7.62mm weapon, which was later modified by changing the declutching feed mechanism which re-designated it as the GAU-17. In 2004 we started transitioning from the XM-218 and GAU-16, which are basically Second World-era M2 Browning machine guns, to the GAU-21A which gives a greater rate-of-fire and greater reliability than previous types, particularly in the desert environment. Right now we are in the middle of integrating the GAU-21A with almost all our platforms."
The Marine Corps refers to the GAU21A as the Common Defensive Weapon System (CDWS), although each aircraft has its own specific crew-served weapon mount. As the CDWS, the USMC has just finished the operational evaluation of the GAU-21A positioned on the ramp of the Bell/Boeing MV-22B Osprey tilt-rotor, and it will certify the GAU-21A on the window, door and ramp positions on the new CH-53K.
Maj. Roland also noted the increased utilisation by the US Navy. "When I began my service, crew-served gunnery was basically 'Marine only', but in recent years the navy has been playing a much larger role with crew-served weapons on their Sikorsky MH-60S/R maritime support helicopters. That is partly due to reduced aircraft types which means each aircraft needs to do more, but it's also a function of the areas where we deploy and operate. These aircraft can carry the M240 and also the GAU-21A, and operating either will depend on the mission at hand and aircraft weight considerations since the GAU-21A weighs more than the M240."
To the north of the USA, the Royal Canadian Air Force (RCAF) has always trained for crew-served air-to-ground gunnery, primarily on their CH-146 Griffon (the local designation for the Bell 412) light utility helicopters. Crews train on both sides of the aircraft with the FN Herstal C6 7.62mm medium machine gun, which is a fully-automatic, air-cooled, gas- and spring-operated machine gun.
The Canadian Armed Forces (CAF) deployed from 2001 as part of the US-led multinational effort to combat Taliban and Al Qaeda insurgents in Afghanistan. This deployment saw an increase in troop injuries and deaths for all of the protagonists primarily due the proliferation of insurgent bombs, so the Royal Canadian Air Force (RCAF) elected to re-introduce the CH-47D for troop and equipment transport. Once this decision was made, it was a natural evolution to have CH-146S provide armed escort.
Lieutenant-Colonel Chris Morrison is the senior staff officer for Tactical Aviation at the 1 Canadian Air Division Headquarters in Winnipeg, Manitoba. He spoke to Armada about the detailed process which the RCAF went through in refining its air-to-ground gunnery capability for combat operations. "As soon as we realised we were going to deploy the CH-146 into theatre, the Directorate of Air Requirements took a very hard look at the C6 door gun that we had been using, and evaluated all of the known limitations ... Once we knew we were deploying we knew we could not bring a 'knife' to a gunfight, both to minimize the risk to the helicopter and crews, as well as being able to more effectively support troops on the ground."
Concurrent to this effort, the RCAF was in the midst of the Interoperable Griffon Reconnaissance Escort Surveillance System (INGRESS) programme which was aimed to install surveillance and targeting turrets in the CH-146 Griffons, and other equipment that would allow for escort missions, namely the acquisition of the FN Herstal GAU-21A/B, which has a range and rate-of-fire (1800 metres/5905 feet and 1200 rounds-per-minute/rpm) that is greater than the C6 (800m/2624.6ft and 800rpm). "The advantage of a GAU-21A/B is the ability to engage at a standoff distance greater than many of the small arms or Rocket Propelled Grenades that our foes were using. The GAU-21A/B also had better stopping power (and) it could penetrate better," said Lt. Col. Morrison.
To start the gunnery refinement process, the RCAF began looking at the offensive tactical employment of door-mounted gunnery through an overall approach consisting of Tactics, Techniques and Procedures (TTPs) for close combat attack. The RCAF was cognisant of two specific combat roles for the CH-146: to provide a force protection capability for the CH47Ds, and to provide force protection for troops on the ground; this could be in the form of airborne convoy escort, or the support of dismounted soldiers. In order to evaluate options, the RCAF looked at allied forces and what they used to fulfil these roles. This included the US Marine Corps UH-IH/Y, the US Army UH-60 family and British Army Air Corps Agusta-Westland AH.1/7 Lynx light-utility helicopters.
According to the RCAF, there are four types of battlefield effects with regards to firepower: harassing fire, suppression fire, neutralising fire and destructive fire. Upon completion of the "allied review" the RCAF drafted a statement of requirements in 2008 with regard to the effects they wanted to deliver in the battlespace, as well as weapons kinetic effects of range and penetrating power, and the quantity of ammunition that the CH-146 could carry.
"One also has to look at the operational employment limitations of a weapon. In the case of door guns, how long can you fire the weapon, what sort of cooling cycles are required, what maintenance cycles are required for the weapon, what maintenance factors are involved with the weapon mounts and magazines, and what effects does using the weapon impart to the helicopter itself. In general, a small calibre Gatling gun usually does not impart too much stress or vibration back into the airframe. For the GAU-21A/B, we had to do some upgrades to hardware components like the lugs for the pintle mount so we could safely fire that weapon from the aircraft to mitigate any risk to the airframe," said Lt. Col. Morrison. "We also looked at retractable weapons mounts for our guns, but hard mounts were the preferred option because we knew that in Afghanistan we could encounter the enemy at any moment; it was a very nonlinear and non-contiguous battlespace. This also allowed us to remove the doors with the added advantage of weight savings." Upon evaluation of the all the options, the RCAF elected to acquire the M134D Gatling gun under Urgent Operational Requirements in three batches: 2008 (three weapons), 2009 (nine weapons), and 2010 (two weapons). The M134D was chosen for its proven reliability and its rate of fire to provide suppression and neutralising fire.
Lt. Col. Morrison was one of the first pilots in the RCAF trained for the new air-to-ground gunnery combat role. He was on the ground in Afghanistan to bring into service the M134D and the GAU-21A/B, and he also flew operational missions in theatre. As a normal load-out, a CH-146 would be configured with both the M134D and GAU-21A/B. Lt. Col. Morrison explained, "With the GAU we are able to exploit great stand off range to produce harassing effects to get the enemy's heads down so we can close-in and use the high rate-of-fire and pinpoint accuracy of the M134D. We found that having a helicopter with these two weapons systems complimented themselves extremely well."
The RCAF was also very focused on the clearance the door guns would have in relation to the airframe in order to give the greatest arc of fire. "We wanted to have as close to a 360 degree field-of-fire as we could get," said Lt. Col. Morrison. "In fact, our pilots would conduct deliberate uncoordinated flight to give a true 360 degree field-of-fire. This is significant because the Taliban had not seen helicopters that had that degree of rear aspect shooting capability. Their typical tactic was to have a helicopter fly by and then engage from behind. They quickly discovered that was not a wise move with our CH-146S."
The acquisition and fielding of both the M134D and GAU-21A/B weapons was a clear example of improving and enhancing an existing capability. According to reports from soldiers, seeing a pair of armed CH-146S overhead was hugely reassuring, and the effects those crews delivered with their weapons saved many lives, either through suppression of the enemy or through neutralisation. "The crew served air-to-ground gunnery capability we have now is a world-class capability. We continue to evolve our TTPs, and we are retaining this skill-set for the future," said Lt. Col. Morrison.
Countless weapon manufacturers produce guns that are suitable for helicopter-mounted air-to-ground gunnery; however, it is clear that some companies stand out, such as Dillon Aero (DA). In the mid-90s, Mike Dillon, owner of Dillon Aero, purchased several surplus M134 family Miniguns and began work on fixing many of the inherent problems (broken bolts, and feeder jams resulting in stoppages) that the weapon was having. By 2003 DA had re-worked, replaced, or improved nearly every component of the system, which is now known as the M134D Minigun. DA also offers a hybrid option, the M134D-H which uses some titanium components to reduce weight for aviation applications. When it comes to the production of guns, DA only manufactures the M134D and M134D-H.
In the flex-fire mode, i.e. when the weapon is mounted on the door or tail gun of a helicopter, the M134D-H is unmatched in the amount of suppressive fire that it is capable of, firing at a rate of 3000rpm. Due to the precision placement of the gun on the DA mounts, the electrically-driven six-barrelled Gatling-style gun is virtually recoilless, which allows the gunner to place more rounds on the target accurately. The proven reliability of the M134D is now an option for the majority of militarised helicopters, and DA's latest helicopter mount is designed to equip Airbus Helicopters' H-225M, AS-332 and AS-532 medium-lift utility rotorcraft families.
Chris Dillon, the company's chief executive officer, told Armada that "an enemy who has positioned themselves to take advantage of this vulnerability can mass his firepower at very close range. The only way to overcome this is with the instantaneous, overwhelming firepower of the M134D. There are machine guns and Gatling guns chambered in larger calibres; however, in the close range, defensive engagement, the larger cartridge is not an advantage for several reasons. First, 12.7mm machine guns fire at a slower rate, denying the user the shot density necessary to achieve instant suppression. Secondly big guns carry fewer rounds, which limit their ability to remain in the fight. Third, bigger guns are just that; bigger. In cramped crew compartments larger weapons hamper the gunners' ability to fight. That said, the main advantage of the .50 calibre gun is that it has a longer range than the 7.62mm Minigun. Long range is definitely a good thing to have when it is needed and there most certainly is a need for 12.7mm weapons for certain offensive missions, but experience dating all the way back to the US involvement in Vietnam, and reinforced by every conflict since, has shown that the greatest threat to the helicopter is an ambush in the landing zone. In this case the high volume fire provided by the M134D is single best solution available."
Regarding the future, Mr. Dillon notes that the company has "several upgrades" to the M134 family planned for the near future. These do not alter the basic nature of the gun but are intended to make operations more efficient. "Having said that, I think it is useful to remember that there is a tendency to 'over engineer' good products. The central components to the weapon, the rotor and receiver, have a service life of 1.5 million rounds, which for most users is effectively infinite. Due to the low impact nature of its rotary design the weapon rarely suffers from part breakage. Over the life of the system the cumulative savings in spares cost, when compared to traditional gas operated machine guns is staggering. However, there are still some good ideas that we are working on which mostly take the form of accessories and are intended to expand the weapons' operating envelope."
Dillon Aero is joined by Belgium's FN Herstal's with products including crew-served or axially-mounted single-barrel automatic machine guns. The company's airborne mounted weapon systems are fully mechanical and do not require any electrical power, making firing possible even if the carrier faces problems. They can integrate two different weapons; either the 12.7mm FN M3M/GAU-21A/B machine gun for outstanding firepower (1100rpm) or a 7.62mm FN MAG 58M/M240 machine gun. To date, FN Herstal airborne weapon systems have been selected to equip more than 2800 helicopters and subsonic aircraft worldwide.
Alongside FN Herstal, continental Europe is home to France's Nexter which offers the SH20 which is a retractable mount system for the firm's M62120mm cannon. The use of this mounting is particularly suitable for missions such as surveillance as the armament is not visible with the helicopter door closed. The SH20 was developed to support French Special Forces, and can outfit new or retrofitted helicopters. It is soon to be qualified on the H-225M. US Ordnance has also recently developed the new M3D 12.7mm weapon system which has a rate of fire of 950rpm. The company states that this is an alternative to the GAU-21A/B and provides the same target effect standards of suppression, neutralisation, and destruction in a cost-effective and simple-to-maintain package.
The spread of helicopter-mounted weapons underscores the ongoing need for this weapon, not only to support troops in contact, but also for Special Forces missions such as Combat Search and Rescue. Crew-served machine guns will undoubtedly be seen as increasingly necessary for all light- and medium-lift utility helicopters likely to be used in the future.
Caption: The Master Gunner sits in the door-gunner's position in a CH-146 Griffon helicopter and fires the new Dillon Aero M134 7.62mm Minigun during a training exercise at at a firing range [C] RCAF
Caption: A helicopter door gunner fires a.50 calibre machine gun at a Mk.25 smoke target during gunnery practice at sea [C]US DoD
Caption: A door gunner assigned to the US Navy 'Dusty Dogs' Helicopter Anti-Submarine Squadron 7 mans a.50 calibre machine gun aboard an SH 60B Seahawk naval support helicopter [C] US DoD
Caption: A Philippine Air Force UH-1H helicopter door gunner stands by before take off during Operation RENAISSANCE which provided humanitarian support to the Philippines following Typhoon Haiyan in December 2013 [C] RCAF
Caption: Two crew chiefs look over the horizon with their .50-cal machine gun and 7-62 Minigun to scan for any enemy targets that might be endangering their UH-IN helicopter [C]USDoD
Caption: A flight engineer keeps close watch using his C-6 machine gun aboard a CH-146 helicopter during a routine air patrol in Bosnia Herzegovina [C]RCAF
Please note: Illustration(s) are not available due to copyright restrictions.