“TheCeļotājs”
"Latvia" Former Soviet Union Military Bases
 
Bell P-39 Airacobra Armament 
 
              
 
Armament
  • Guns:
    • 1 x 37mm M4 Cannon with 30 Rounds of HE Ammo 
    • 2 x .50 cal "12.7mm" Machine Guns, 200 Rounds per Nose-Gun 
    • 4 x .30 cal Machine Guns, Wing Mounted. 300 Rounds per Wing-Pod 
  • Bombs: Up to 500 pounds "230kg" of bombs externally
37mm Automatic Gun, M4 
 
    
                                                                 37mm M4 Cannon
 
37mm Automatic Gun, M4
  • Type: Auto-Cannon 
  • Place of Origin: United States
Service History
  • In Service: 1939
  • Used by: United States
  • Wars: World War II
Production History
  • Designer: John Browning
  • Designed: 1921-1938
  • Manufacturer: Colt
  • Produced: 1939
Specifications
  • Weight: 213 pounds "97kg
  • Length: 89.5 inches "2.27m"
  • Caliber: 37mm "1.46 inches"
  • Action: Recoil Operation
  • Recoil: 9⅝ inches "245mm"
  • Rate of Fire: 150 rpm 
  • Muzzle Velocity: 2,000 ft/s "610 m/s"
  • Feed System: 30 Round Magazine
The 37mm Automatic Gun, M4, known as the T9 during development, was a 37mm "1.46 inches" auto-cannon designed by John Browning and used in the Bell P-39 Airacobra and P-63 Kingcobra fighters, as well as experimentally on other designs. It provided interceptors with a weapon that could shoot down any bomber with as little as one hit. It was a compact design with a relatively low muzzle velocity and rate of fire.
 
Design
 
Designed primarily as an anti-aircraft weapon, the gun had a muzzle velocity of 2,000 ft/s "610 m/s" and a cyclic rate of 150 rounds per minute. It was normally loaded with high-explosive shells, but could also be loaded with the M80 armor-piercing shell, which could penetrate 1 inches "25mm" of armor plate at 500 yards "460m". It was magazine-fed and could be fired manually or by remote control through a solenoid mounted on the rear of the gun.
 
Recoil and counter-recoil were controlled hydraulically by means of a piston and spring combination connected to the recoiling parts and operating in an oil-filled recuperator cylinder mounted to the stationary trunnion block assembly. The recoiling parts of the gun included the tube and tube extension, the recuperator piston and piston rod, the lock frame assembly, the driving spring assemblies, and the breechblock assembly. The non-recoiling parts included the trunnion block group, the feed box and feeding mechanism, the recuperator cylinder and bushing, the back plate group, and the manual charger assembly.
 
Feeding Mechanism
 
As the gun was originally designed, ammunition could be fed by a 5 round clip, a 15 round link belt, or a non-disintegrating 30 round endless belt magazine. The 30 round endless belt version was used exclusively in production. The M4 gun fed only from the left.
 
    
   37mm M4 Cannon Rounds and 30 Round Magazine
 
The 30-round Endless Belt Magazine, M6, was an oval-shaped framework nicknamed a "Horsecollar Magazine", from its shape providing a track for the endless belt. The articulated link belt actually contained 33 rounds: consisting of 30 HE and/or AP shells and three tracer rounds "one at the end of each 10 shell section" to improve accuracy.
 
Firing Cycle
 
Initial loading and cocking of the gun were accomplished manually. A safety feature incorporated in the design of the trigger mechanism prevented firing the round until the breech-block assembly was in the battery position.
 
The breech was locked and unlocked by recoil action which brings the operating level guide pins against cams to raise and lower the breechblock. The function of the breechblock was to assist in the final chambering of the round, close the breech, and actuate the trigger trip. It also provided a mounting for the firing pin.
 
The lock frame, during automatic firing, was retracted by recoil action and is forced forward by the driving springs. The major function of the lock frame assembly was to force the cartridge into the chamber, actuate the breechblock, fire the round by means of the hammer striking the firing pin, extract the cartridge case from the chamber, and operate the ejector.
 
The back plate assembly, by absorbing the energy of the lock frame, reduced the shock against the carrier pin as the lock frame was hatched to the rear.
 
The driving spring assemblies held the lock frame against the carrier dog until the carrier was released by carrier catch which was pivoted by the incoming round. The springs then drove the lock frame assembly forward to operate the ejector, chamber the round and raise the breechblock.
 
Initial extraction occurred during recoil. Extraction, ejection, feeding and loading were accomplished during counter-recoil. If the trigger was held in the firing position, the gun would continue to fire automatically until the magazine was empty.
 
Ammunition
 
Ammunition was issued in the form of fixed rounds, consisting of H.E. shell, M54, with P.D. fuse, M56; practice shell, M55A1, with dummy fuse, M50; and A.P. shot, M80.
 
The rapid strides in aircraft protection made it necessary to develop an aircraft weapon that would fire projectiles with greater explosive and armor-piercing qualities than smaller caliber weapons. As a result, the 37mm "1.46 inches" automatic gun, M4, was developed and standardized for aircraft use.
 
The 37mm gun "1.46 inches", M4, used the same high-explosive "M54" and practice "M55A1" projectiles as the 37mm "1.46 inches" antiaircraft gun, M1A2, but different cartridge cases are necessary due to the larger chamber of the M4 gun.
 
However, the overall length of the armor-piercing projectiles, M51 and M74, which were used in the M3A1, M5A1 and M6 tank and antitank guns, was too great to permit their use in the M4 gun and the 37mm "1.46 inches" armor-piercing shot, M80, was developed and standardized.
 
    
                      "HE" High-Explosive Shell, 37mm, M54 standard
 
This shell used the M56 point detonating fuse. The complete round weighs 1.99 pounds "900g"; as fired, the projectile weighs 1.34 pounds "608g". The 0.16 pounds "70g" charge of M2 powder is a Hercules NG formula of single perforated grains with 0.030 inches "0.76mm" web and gives the projectile the prescribed muzzle velocity of 2,000 ft/s "610m/s".
 
The M54 used a shell-destroying tracer in addition to the point-detonating fuze. The tracer had a burning time of three seconds at the end of which it set off an igniting relay charge of 1.68gr "0.109g" of Grade A-5 Army Black Powder which ignited a relay pellet that detonated the charge, destroying the shell before ground impact.
 
The bursting charge of tetryl weighed 0.10 pounds "45g", and the alternate Composition "A" charge weighs 0.105 pounds "48g". The tetryl loading consisted of a 200gr "13g" tetryl pellet pressed into the shell cavity under 9,000-10,000 psi "60-70 MPa" pressure and the remainder of the charge of two equal increments pressed under approximately 9,000 psi "60 MPa" pressure. The Composition "A" bursting charge is loaded in the same manner as the tetryl charge, except that the relay pellet with the Composition "A" weighs 36gr "2.3g" as against 23gr "1.5g" for the pellet used with the tetryl load.
 
Practice Shell, 37mm, M55A1 standard
 
This shell was the high-explosive shell modified slightly for practice purposes. It contained a red tracer and a dummy fuse "M50, M50B1, M50B2 or M50B3". The M50 dummy fuze was made from a plastic composition and the M50B1, M50B2 and M50B3 fuses were made from low carbon steel machined to give the same contour and weight as the point-detonating fuse, M56, used with the M54 projectile.
 
As used in the M4, the complete round weighed 1.99 pounds "900g", and as fired the shell weighed 1.34 pounds "610g". The 0.16 pounds "70g" charge of M2 powder was Hercules NG formula of single perforated grains with a 0.030 inches "0.76mm" web and gave the prescribed muzzle velocity of 2,000 ft/s "610 m/s".
 
Armor-Piercing Shot, 37mm, M80 standard
 
The AP shot was a mono-block projectile with a tracer element of three seconds burning time. It did not need a fuse or bursting charge. The weight of the complete round was 2.31 pounds "1.05kg", the weight of the AP shot was 1.66 pounds "750g". The propelling charge was 0.15 pounds "78g" of M2 powder of a Hercules NG formula with a single-perforated grain and 0.030 inches "0.76mm" web.
 
Use
 
The only aircraft to see service use of the M4 were the Bell P-39 Airacobra and the derivative P-63 Kingcobra, both of which saw action with the Soviet Air Forces on the Eastern Front. The U.S did not supply M80 armor-piercing rounds for the auto-cannons of Soviet P-39s, instead, the Soviets received 1,232,991 M54 high-explosive rounds which the Soviets sometimes used against soft ground targets but primarily for air-to-air combat. The Soviets did not use the P-39 for tank-busting.
 
The M4 37mm "1.46 inches" automatic cannon was mounted on numerous U.S. Navy PT boats as deck guns, beginning with the Solomon Islands campaign. At first, they were cannibalized from crashed P-39s at Henderson field, and due
to their success as an anti-barge weapon were used for the rest of the war. Beginning in 1944, the M9 model 37mm "1.46 inches" cannon was installed at the builders' boatyard as standard equipment. The M4s were initially mounted on a simple pedestal mount "often built at the front lines" with the standard horseshoe endless-belt feed being used. Later, an improved pedestal mount was designed for original equipment mountings on the boats. Handgrips of several figurations were used with various sights being tried. Most PT boat gunners used tracers to sight the fall of their shot. Primary targets were the landing barges being used to move supplies down the island chain at night.
 
The M2 Machine Gun / Browning .50 Caliber Machine Gun
 
    
                                 .50 cal "12.7 mm" Machine Guns, 200 rounds per nose-gun
 
Browning Machine Gun, Cal. .50, M2, HB
 
    
 
The M2 Machine Gun / Browning .50 Caliber Machine Gun, is a heavy machine gun designed towards the end of World War I by John Browning. It is very similar in design to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge. The M2 uses the much larger and much more powerful .50 BMG cartridge, which was developed alongside and takes its name from the gun itself "BMG standing for Browning Machine Gun". The M2
has been referred to as "Ma Deuce", or "the fifty" in reference to its caliber. The design has had many specific designations; the official designation for the current infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible. It is effective against infantry, unarmored or lightly armored vehicles and boats, light fortifications and low-flying aircraft.
 
The Browning .50 caliber machine gun has been used extensively as a vehicle weapon and for aircraft armament by the United States from the 1920s to the present. It was heavily used during World War II, the Korean War, the Vietnam War, and during operations in Iraq and Afghanistan in the 2000s "decade". It is the primary heavy machine gun of NATO countries, and has been used by many other countries. The M2 has been in use longer than any other small arm in
U.S. inventory except the .45 ACP M1911 pistol, also designed by John Browning.
 
The M2HB is manufactured in the United States by General Dynamics and U.S. Ordnance  for use by the United States government, and for US Foreign Allies via FMS sales. FN Herstal has manufactured the M2 machine gun since the 1930s. U.S. Ordnance developed their M2 Quick Change Barrel system after years of manufacturing machine guns for the U.S. Department of Defense and U.S. allies. 
 
History
 
The United States did not have many machine guns when it entered World War I, and most were old technology. The machine gun was heavily used in World War I, and weapons of larger than rifle caliber were appearing. Both the British and French had large caliber machine guns. The larger rounds were needed to defeat the armor that was being introduced to the battlefield. Armor was also appearing in the skies. During World War I, the Germans introduced a heavily armored airplane, the Junkers J.I. The armor made aircraft machine guns using conventional rifle ammunition "such as the .30-06" ineffective. The United States became keenly aware of this problem when Quentin Roosevelt's aircraft was shot down.
 
Consequently, American Expeditionary Force's commander General John J. Pershing asked for a larger caliber machine gun. Pershing asked the Army Ordnance Department to develop a machine gun with a caliber of at least 0.50 inches "12.7mm" and a muzzle velocity of at least 2,700 feet per second "820 m/s". U.S. Col. John Henry Parker, commanding a machine gun school in France, observed the effectiveness of a French 11 mm "0.43 inches" incendiary armor-piercing round. The Army Ordnance Department ordered eight experimental Colt machine guns re-chambered for the French 11mm cartridge. The French had developed a prototype machine gun for an even larger caliber.
 
The French 11mm round was not suitable because its velocity was too low. Pershing wanted a bullet of at least 670gr "43 g" and a muzzle velocity of 2,700 ft/s "820 m/s". Development with the French round was dropped. 
 
Around July 1917, John M. Browning started redesigning his .30 caliber machine for a larger caliber. Winchester worked on the cartridge, which was a scaled up version of the .30/06. Winchester initially added a rim to the cartridge because it wanted to use the cartridge in an anti-tank rifle, but Pershing insisted the cartridge be rimless. The first .50 machine gun underwent trials on 15 October 1918. It fired at less than 500 rounds per minute, and the muzzle velocity was only 2,300 ft/s "700 m/s". Cartridge improvements were promised. The gun was heavy, difficult to control, fired too slowly for anti-personnel, and was not powerful enough against armor.
 
While the .50 was being developed, some German anti-tank rifles and ammunition were seized. The German rounds had a muzzle velocity of 2,700 ft/s "820 m/s", an 800gr "52 g" bullet, and could pierce 1 inch "25mm" at 250 yards "230 m". Winchester made the .50 caliber round have similar performance. Ultimately, the muzzle velocity was 2,750 ft/s "840 m/s". 
 
Efforts by John M. Browning and Fred T. Moore resulted in the water-cooled Browning machine gun, caliber .50, M1921. An aircraft version was termed the Browning aircraft machine gun, caliber .50, M1921. These guns were used experimentally from 1921 until 1937. They had light-weight barrels and the ammunition only fed from the left side. Service trials raised doubts whether the guns would be suitable for aircraft or for anti-aircraft use. A heavy barrel M1921 was considered for ground vehicles.
 
John M. Browning died in 1926. Between 1927 and 1932, Dr. S. H. Green studied the design issues and service needs. The result was a single receiver design that could be turned into seven types of .50 caliber machine guns by using different jackets, barrels, and other components. The new receiver allowed right or left hand feed. In 1933, Colt manufactured several prototype Browning machine guns "including what would be known as the M1921A1 and M1921E2". With support from the Navy, Colt started manufacturing the M2 in 1933.
 
A variant without a water jacket, but with a thicker-walled, air-cooled barrel was designated the M2 HB "HB for Heavy Barrel". The added mass and surface area of the heavy barrel compensated somewhat for the loss of water-cooling, while reducing bulk and weight: the M2 weighs 121 pounds "55kg" with a water jacket, but the M2 HB weighs 84 pounds "38kg". Due to the long procedure for changing the barrel, an improved system was developed called QCB "quick change barrel". The lightweight AN/M2 "light-barrel" version of the Browning M2 weighing 60 pounds "27kg" was also developed, and became the standard aviation machine gun of the World War II-era For American military aircraft of nearly every type.
 
Design Details
 
The Browning M2 is an air-cooled, belt-fed machine gun. The M2 fires from a closed bolt, operated on the short recoil principle. The M2 fires the .50 BMG cartridge, which offers long range, accuracy and immense stopping power. The closed bolt firing cycle made the M2 usable as a synchronized machine gun on aircraft before and during World War II, as on the early versions of the Curtiss P-40 fighter.
 
The M2 is a scaled-up version of John Browning's M1917 .30 caliber machine gun "even using the same timing gauges".
 
Features
 
The M2 has varying cyclic rates of fire, depending upon the model. The M2HB "heavy barrel" air-cooled ground gun has a cyclic rate of 450-575 rounds per minute. The early M2 water-cooled AA guns had a cyclic rate of around 450–600 rpm. The AN/M2 aircraft gun has a cyclic rate of 750–850 rpm; this increases to 1,200 rpm or more for AN/M3 aircraft guns fitted with electric or mechanical feed boost mechanisms. These maximum rates of fire are generally not achieved in use, as sustained fire at that rate will wear out the bore within a few thousand rounds, necessitating replacement. For the M2HB, slow fire is less than 40 rounds per minute and rapid fire more than 40 rounds per minute. 
 
The M2 has an effective range of 1,830 meters "2,000 yards" and a maximum effective range of 2,000 meters "2,200 yards" when fired from the M3 tripod. In its ground-portable, crew-served role as the M2HB, the gun itself weighs in at a hefty 84 pounds "38kg", and the assembled M3 tripod another 44 pounds "20kg". In this configuration, the V-shaped "butterfly" trigger is located at the very rear of the weapon, with a "spade handle" hand-grip on either side of it and the
bolt release the center. The spade handles are gripped and the butterfly trigger is depressed with one or both thumbs. Recently new rear buffer assemblies have used squeeze triggers mounted to the hand grips, doing away with the butterfly triggers.
 
When the bolt release is locked down by the bolt latch release lock on the buffer tube sleeve, the gun functions in fully automatic mode. Conversely, the bolt release can be unlocked into the up position resulting in single-shot firing "the gunner must press the bolt latch release to send the bolt forward". Unlike virtually all other modern machine guns, it has no safety "although a sliding safety switch has recently been fielded to USMC armories for installation on their weapons". Troops in the field have been known to add an improvised safety measure against accidental firing by slipping an expended shell casing under the butterfly trigger.
 
Because the M2 was intentionally designed to operate in many configurations, it can be adapted to feed from the left or right side of the weapon by exchanging the belt-holding pawls, and the front and rear cartridge stops "three-piece set to include link stripper", then reversing the bolt switch. The operator must also convert the top-cover belt feed slide assembly from left to right hand feed as well as the spring and plunger in the feed arm. This will take a well trained individual less than two minutes to perform.
 
The charging assembly may be changed from left to right hand charge. A right hand charging handle spring, lock wire and a little know how are all that are required to accomplish this. The M2 can be battle ready and easily interchanged if it is preemptively fitted with a retracting slide assembly on both sides of the weapon system. This eliminates the need to have the weapon removed from service to accomplish this task.
 
Ammunition
 
There are several different types of ammunition used in the M2HB and AN aircraft guns. From World War II through the Vietnam War, the big Browning was used with standard ball, armor-piercing "AP", armor-piercing incendiary "API", and armor-piercing incendiary tracer "APIT" rounds. All .50 ammunition designated "armor-piercing" was required to completely perforate 0.875 inches "22.2mm" of hardened steel armor plate at a distance of 100 yards "91mm" and
0.75 inches "19 mm" at 547 yards "500 m". The API and APIT rounds left a flash, report, and smoke on contact, useful in detecting strikes on enemy targets; they were primarily intended to incapacitate thin-skinned and lightly armored vehicles and aircraft, while igniting their fuel tanks.
 
Current ammunition types include: M33 Ball "706.7 grain" for personnel and light material targets, M17 tracer, M8 API "622.5 grain", M20 API-T "619 grain", and M962 SLAP-T. The latter ammunition along with the M903 SLAP "Saboted Light Armor Penetrator" round can perforate 1.34 inches "34 mm" of HHA "face-hardened steel plate" at 500 meters "550 yards", 0.91 inches "23mm" at 1,200 meters "1,300 yards", and 0.75 inches "19 mm" at 1,500 meters "1,600 yards". This is achieved by using a 0.30-inch-diameter "7.6mm" tungsten penetrator. The SLAP-T adds a tracer charge to the base of the ammunition. This ammunition was type classified in 1993. 
 
When firing blanks, a large blank-firing adapter "BFA" must be used to keep the gas pressure high enough to allow the action to cycle. The adapter is very distinctive, attaching to the muzzle with three rods extending back to the base. The BFA can often be seen on M2s during peacetime operations.
 
Deployment
 
The M2 .50 Browning machine gun has been used for various roles:
  • A medium infantry support weapon
  • As an anti-aircraft "AA" gun in some ships; up to six M2 guns could be mounted on the same turret.
  • As an anti-aircraft gun on the ground. The original water-cooled version of the M2 was used on a tall AA tripod or vehicle-mounted anti-aircraft weapon on a sturdy pedestal mount. In later variants, twin and quadruple M2HB Browning's were used, such as the M45 Quadmount used on the US M16 half-track carrier. Twin or quad-mount .50 M2 guns normally used alternating left-hand and right-hand feed.
  • Primary or secondary weapon on an armored fighting vehicle.
  • Primary or secondary weapon on a naval patrol boat.
  • Spotting for the primary weapon on some armored fighting vehicles.
  • Secondary weapon for anti-boat defense on large naval vessels "corvettes, frigates, destroyers, cruisers, etc.".
  • Coaxial gun or independent mounting in some tanks.
  • Fixed-mounted primary armament, with the AN/M2 light-barrel version only, in World War II-era U.S. aircraft such as the P-47 Thunderbolt, P-51 Mustang, and the Korean-era U.S. F-86 Saber, sometimes synchronized to fire through the propeller arc in a twin mount atop the engine, as on the P-40B Tomahawk fighter.
  • Turret-mount or flexible-mounted defensive armament, again only with the AN/M2 light-barrel version, in World War II-era bombers such as the B-17 Flying Fortress, and B-24 Liberator.
United States
 
At the outbreak of the Second World War the United States had versions of the M2 in service as fixed aircraft guns, anti-aircraft defensive guns "on aircraft, ships, or boats", infantry "tripod-mounted" guns, and as dual purpose anti-aircraft and anti-vehicular weapons on vehicles.
 
The .50 AN/M2 light-barrel aircraft Browning used in planes had a rate of fire of approximately 800 rounds per minute, and was used singly or in groups of up to eight guns for aircraft ranging from the P-47 Thunderbolt to the B-25 Mitchell bomber, which in the last J-version of the Mitchell could have upwards of fourteen M2s firing forward for ground attack missions - eight in a solid metal-structure nose, four more mounted in a pair of conformal twin-gunned gun pods on the lower cockpit sides, and two more if the forward dorsal turret's pair of M2 guns were also aimed straight forward.
 
In the dual-purpose vehicle mount, the M2HB "heavy barrel" proved extremely effective in U.S. service: the Browning's .50 caliber AP and API rounds could easily penetrate the engine block or fuel tanks of a German Bf 109 fighter attacking at low altitude, or perforate the hull plates and fuel tanks of a German half-track or light armored car. While the dual-purpose mounting was undeniably useful, it did normally require the operator to stand when using the M2 in a ground role, exposing him to return fire. Units in the field often modified the mountings on their vehicles, especially tanks and tank destroyers, to provide more operator protection in the anti-vehicular and anti-personnel role. The weapon was particularly hated by the Germans, whose attacks and ambushes against otherwise helpless stalled motor convoys were frequently broken up by .50 caliber machine gun fire. Vehicles would frequently "recon by fire" with the M2 Browning i.e. firing continuously at suspected points of ambush while moving through areas still containing enemy forces. One vehicle would fire exclusively to the right, the following vehicle to the left, the next one to the right, and so on in
order to cover both flanks of the advancing convoy.
 
Besides vehicle-mounted weapons, the heavy weapons companies in a World War II U.S. Army infantry battalion or regiment were each issued one M2 Browning with tripod "ground" mount. Mounted on a heavily sandbagged tripod, the M2HB proved very useful in either a defensive role or to interdict or block road intersections from use by German infantry and motorized forces. The hammering of a heavy Browning could usually be relied upon to put a German infantry company face-down in the dirt. There are numerous instances of the M2 Browning being used against enemy personnel, particularly infantry assaults  or for interdiction or elimination of enemy artillery observers or snipers at distances too great for ordinary infantry weapons. 
 
The M2HB was not widely used in the Pacific campaign, due to several factors, including weight, the inherent nature of infantry jungle combat, and because road intersections were usually easily outflanked. However, it was used by fast-moving motorized forces in the Philippines to destroy Japanese blocking units on the advance to Manila. The quad mount .50 was also used to destroy Japanese emplacements.
 
Aircraft Guns AN/M2
 
The M2 machine gun was widely used during World War II and in later postwar conflicts as a remote or flexible aircraft gun. For fixed "offensive" or flexible "defensive" guns used in aircraft, a dedicated M2 version was developed called the .50 Browning AN/M2. The "AN" stands for "Army/Navy", since the gun was developed jointly for use by both services "unusual for the time, when the delineations between the Army and Navy were much stricter, and relations between armed services were often cool, if not outright hostile". The AN/M2 had a cyclic rate of 750–850 rounds per minute, with the ability to be fired from an electrically operated remote-mount solenoid trigger when installed as a fixed gun. Cooled by the aircraft's slip-stream, the air-cooled AN/M2 was fitted with a substantially lighter barrel, which also had the effect of increasing the rate of fire. The official designation for this weapon was Browning Machine Gun, Aircraft, Cal. .50, AN/M2 "Fixed" or "Flexible".
 
The XM296/M296 is a further development of the AN/M2 machine gun for the OH-58 Kiowa Warrior helicopter. The M296 differs from previous remote firing variants in that it has adjustable firing rate "500–850 rpm", while lacking a bolt latch "allowing single-shot operation".  As an air-cooled gun used aboard a relatively slow rotary-wing aircraft, the M296 has a burst restriction rate of 50 rounds per minute sustained fire or 150 rounds per minute maximum while  conducting peacetime training requirements; the combat firing rate is unrestricted but does mandate a ten-minute cooling period after prolonged firing to avoid stoppages due to overheating.
 
AN/M3, GAU-21/A, and M3P
 
During World War II, a faster-firing Browning was developed for aircraft use. The AN/M3 features a mechanical or electrically boosted feed mechanism to increase the rate of fire to around 1,200 rounds per minute. The AN/M3 was used in Korea on the F-86 Saber, and in Vietnam in the XM14/SUU-12/A gun pod. Today, it can be found on the Embracer EMB 314 Super Tucano.
 
The FN Herstal license-produced M3-series is used by the U.S. military in two versions; the M3M and M3P. The fixed, remote-firing version, the FN M3P, is employed on the Avenger Air Defense System, and is currently being used on the OH-58D; augmenting the XM296 .50 cal. machine gun. The M3M flexible machine gun has been adopted by USN under the designation GAU-21/A for use on helicopters. The GAU-21/A is also being used by the United States Marine
Corps to upgrade from the XM-218/GAU-16 .50 cal. machine gun for the CH-53E, on the UH-1Y Venom, and on the Canadian Forces' CH-146 Griffon via the INGRESS upgrade.
 
M1919 Browning Machine Gun
 
    
 
Gun, Machine, Caliber .30, Browning, M1919A4
 
    
 
The M1919 Browning is a .30 caliber medium machine gun that was widely used during the 20th century. It was used as a light infantry, coaxial, mounted, aircraft, and anti-aircraft machine gun by the U.S. and many other countries, especially during World War II, the Korean War, and the Vietnam War. Although it began to be superseded by newer designs in the later half of the century "such as by the M60 machine gun", it remained in use in many North Atlantic Treaty Organization [NATO] countries and elsewhere for much longer. It is very similar in design to the larger .50 caliber "12.7mm" M2 Machine Gun, which is also a Browning-designed weapon and is still in [NATO] service.
 
Many M1919s were re-chambered for the new 7.62×51mm [NATO] round and served into the 1990s, as well as up to the present day in some countries. The United States Navy also converted many to 7.62mm [NATO], and designated them Mk 21 Mod 0; they were commonly used on river craft in the 1960s and 1970s in Vietnam.
 
The M1919 was an air-cooled development of the standard US machine gun of World War I, the Browning M1917, as designed by John M. Browning.
 
Operation
 
Loading
 
The M1919 originally fired the .30 cal M1906 "30-06" ball cartridge, and later the .30 caliber M2 ball cartridge, contained in a woven cloth belt, feeding from left to right. A metallic link was later adopted, forming a "disintegrating" belt.
 
Loading was accomplished by inserting the pull tab on the ammunition belt from the left side of the gun "either metal links or metal tab on cloth belts", until the belt- holding pawl at the entrance of feed way grabbed the belt and held it in place. The cocking handle was then pulled back "hand palm-up, to avoid thumb dislocation from a potential 'hot-barrel-cooked-off' round, *see below for explanation", and released. This advanced the first round of the belt in front of the bolt for the extractor/ejector on the bolt to grab the first cartridge. The cocking handle was pulled and released a second time. This removed the first cartridge from the belt, advanced the next round into position to be grabbed and moved the first round down into the chamber of the barrel ready for firing.
 
As the bolt went into battery "ready to fire" position the extractor grabbed the next round on the belt that was advanced and was resting in the feed way waiting to be loaded. Every time the gun fired, the gun performed the simultaneous operations of ejecting the spent round, loading the next round to be fired into the barrel, advancing the belt, and grabbing the next round in preparation for loading again.
 
The gun's original design was as a water cooled machine gun. When it was decided to try to lighten the gun and make it an air cooled gun, its design as a gun that fires from the closed bolt created a potentially dangerous situation. If the gun was very hot from prolonged firing, the cartridge ready to be fired could be resting in a red hot barrel, causing the propellant in the round to "cook off" firing from the intense heat without any warning.
 
Firing
 
When the rear of the trigger was pivoted upwards by the operator, the front of the trigger tipped downward, releasing the sear, and the sear, in turn, released the firing pin allowing it to strike the primer of the cartridge.
 
As the assembly of bolt, barrel and barrel extension recoiled to the rear of the gun, following the firing of the cartridge, the locking block which locked the bolt to the barrel and barrel extension was drawn out of engagement by a cam in the bottom of the gun's receiver. The recoiling barrel extension struck the "accelerator" assembly, a half-moon shaped piece pivoting from the front of the lock frame. The tips of the accelerator's two curving fingers engaged the bottom of the bolt and caused it to move rapidly to the rear, extracting the fired cartridge casing from the barrel. A track in the top of the bolt caused the feed mechanism to advance, providing a new cartridge to be chambered as the bolt moved forward under pressure from the recoil spring. If the trigger was still being pressed, the cycle then repeated itself.
 
Operational use
 
Infantry
 
As a company or battalion support weapon, the M1919 required at least a two-man machine gun team. But in practice, four men were normally involved: the gunner "who fired the gun and when advancing carried the tripod and box of ammo", the assistant gunner "who helped feed the gun and carried the gun, and box of spare parts and tools", and two ammunition carriers. The original idea was to allow the gun to be more easily packed for transport, and featured a light barrel and bipod when first introduced as the M1919A1. Unfortunately, it quickly became clear that the gun was too heavy to be easily moved, while at the same time too light for sustained fire. This led to the M1919A2, which included a heavier barrel and tripod, and could be continuously fired for longer durations.
 
The M1919A4 weighed about 31 pounds "14kg", and was ordinarily mounted on a lightweight, low-slung tripod for infantry use. Fixed vehicle mounts were also employed. It saw wide use in World War II mounted on jeeps, armored personnel carriers, tanks, and amphibious vehicles. The M1919A4 played a key role in the firepower of the World War II US Army infantry company normally had a weapons platoon in addition to its other organic units. The presence of M1919A4 weapons in the weapons platoon gave company commanders additional automatic fire support at the company level, whether in the assault or on defense. 
 
The A5 was an adaptation of the A4 with a forward mounting point to allow it to be mounted in tanks and armored cars. This, along with the M37 and the Browning M2 machine gun, was the most common secondary armament during World War II for the Allies.
 
Another version of the M1919A4, the M1919A6, was an attempt to make the weapon into a light machine gun by attaching a butt stock and lighter barrel 4 pounds "1.8kg" instead of 7 pounds "3.2kg". The A6 version was in fact heavier than the A4 without its tripod, at 32 pounds "15kg", though its bipod made for faster deployment and enabled the machine gun team to dispense with one man "the tripod bearer". The A6 version saw increasing service in the latter days of World War II and was used extensively in Korea. The A6 variant had a folding bipod mounted on the front of the gun, a sheet-metal butt stock, carrying handle, and a tapered barrel. While the modifications were intended to make the weapon more useful as a squad light machine gun, it was a stopgap solution, as the M1919A6 was heavier than the old Lewis gun of World War I, let alone the contemporary light machine guns of other nations.
 
During the Second World War, two additional variants of the M1919 were adopted by the US military. One version was the coaxial M37 variant, with the ability to feed from either the left or the right of the weapon. The M37 also featured an extended charging handle similar to those on the M1919A4E1 and A5. A trial variant fitted with special sighting equipment was designated M37F.
 
In the late 1950s, a M1919 designed for remote firing via a solenoid trigger was developed for use in the XM1/E1 armament subsystem was designated M37C. The US Navy later converted a number of M1919A4s to 7.62mm [NATO]
chambering and designated them Mk 21 Mod 0; some of these weapons were employed in Vietnam in riverine warfare patrols.
 
From the 1960s until the 1990s, the Israel Defense Forces "IDF" used ground tripod and vehicle-mounted M1919A4 guns converted to 7.62mm NATO on many of their armored vehicles and M3 personnel carriers. Israel developed a modified link for these guns due to feeding problems with the original US M1 link design. The improved Israeli link worked with .30 caliber, 7.62mm [NATO] and 8×57mm cartridges.
 
Aircraft
 
With assistance from firearms engineers at Fabrique Nationale de Herstal, Belgium, the Model 1919 was completely re-engineered into the .30 caliber M2 AN "Army-Navy" aircraft machine gun. The .30 in M2 AN Browning was widely adopted as both a fixed "offensive" and flexible "defensive" weapon on aircraft. Aircraft machine guns required light weight, firepower, and reliability, and achieving all three goals proved a difficult challenge. The receiver walls and operating components of the M2 were made thinner and lighter, and with air cooling provided by the speed of the aircraft, designers were able to reduce the barrel's weight and profile. As a result, the M2 weighed two-thirds that of the 1919A4, and the lightened mechanism gave it a rate of fire approaching 1,200 rpm "some variants could achieve 1,500 rpm", a necessity for engaging fast-moving aircraft. The M2's feed mechanism had to lift its own loaded belt out of the ammunition box and feed it into the gun, equivalent to a weight of 11 pounds "5kg". In Ordnance circles, the .30 M2 AN Browning had the reputation of being the most difficult-to-repair weapon in the entire US small arms inventory. 
 
The M2 also appeared in a twin-mount version which paired two M2 guns with opposing feed chutes in one unit for operation by a single gunner, with a combined rate of fire of 2,400 rpm. All of the various M2 models saw service in the early stages of World War II, but were phased out beginning in 1943, as hand-trained defensive machine guns became obsolete for air warfare "the .50in/12.7mm M2 Browning and 20mm automatic cannon had replaced the .30 in as offensive air armament as well". The .30 in M2 aircraft gun was widely distributed to other US allies during and after World War II, and in British and Commonwealth service saw limited use as a vehicle-mounted anti-aircraft or anti-personnel machine gun. 
 
On Soviet Aircraft
 
The .303 variant equipped the Hawker Hurricanes delivered to Soviet Air Forces, during the Great Patriotic War. Soviet airmen compared them to Soviet ShKAS in terms of reliability: "But they often failed due to dust," recalled pilot Nikolai G. Golodnikov. "We tackled the problem by gluing percale on all the machine-gun holes, and when you opened fire, bullets went right through. The machine guns became reliable then. They were of low efficiency when fired from  distances of 150-300m." 
 
 
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Revised: 01/29/2013 – 09:12:25