M4 cannon
Encyclopedia
The 37 mm Automatic Gun, M4, known as the T9 during development, was a 37 mm (1.46 in) autocannon
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 interceptor
s 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.
of 2000 ft/s (609.6 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 in (25 mm) of armor plate
at 500 yd (457.2 m). 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 nonrecoiling 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.
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.
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 3 tracer rounds (one at the end of each 10-shell section) to improve accuracy.
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The lock frame, during automatic firing, was retracted by recoil action and is forced forward by the driving springs.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.
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 37 mm (1.46 in) automatic gun, M4, was developed and standardized for aircraft use.
The 37 mm gun (1.46 in), M4, used the same high-explosive (M54) and practice (M55A1) projectiles as the 37 mm (1.46 in) 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 37 mm (1.46 in) armor-piercing shot, M80, was developed and standardized.
High-explosive shell, 37 mm, M54 standard
This shell used the M56 point detonating fuse. The complete round weighs 1.99 lb (900 g); as fired, the projectile weighs 1.34 lb (608 g). The 0.16 lb (70 g) charge of M2 powder is a Hercules NG formula of single perforated grains with 0.030 in (0.76 mm) web and gives the projectile the prescribed muzzle velocity of 2000 ft/s (609.6 m/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 1.68 gr 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 lb (45 g), and the alternate Composition "A" charge weighs 0.105 lb (48 g). The tetryl loading consisted of a 200 gr (13 g) 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 36 gr as against 23 gr for the pellet used with the tetryl load.
Practice shell, 37 mm, 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 lb (900 g), and as fired the shell weighed 1.34 lb (610 g). The 0.16 lb (70 g) charge of M2 powder was Hercules NG formula of single perforated grains with a 0.030 in (0.76 mm) web and gave the prescribed muzzle velocity of 2000 ft/s (609.6 m/s).
Armor-piercing shot, 37 mm, M80 standard
The AP shot was a monoblock 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 lb (1.05 kg), the weight of the AP shot was 1.66 lb (750 g). The propelling charge was 0.15 lb (78 g) of M2 powder of a Hercules NG formula with a single-perforated grain and 0.030 in (0.76 mm) web.
, 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 autocannons 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 37 mm (1.46 in) automatic cannon was mounted on numerous US Navy
PT boat
s 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 37 mm (1.46 in) 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 configurations 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.
Autocannon
An autocannon or automatic cannon is a rapid-fire projectile weapon firing a shell as opposed to the bullet fired by a machine gun. Autocannons often have a larger caliber than a machine gun . Usually, autocannons are smaller than a field gun or other artillery, and are mechanically loaded for a...
designed by John Browning
John Browning
John Moses Browning , born in Ogden, Utah, was an American firearms designer who developed many varieties of military and civilian firearms, cartridges, and gun mechanisms, many of which are still in use around the world...
and used in the Bell P-39 Airacobra and P-63 Kingcobra
P-63 Kingcobra
The Bell P-63 Kingcobra was a United States fighter aircraft developed in World War II from the Bell P-39 Airacobra in an attempt to correct that aircraft's deficiencies...
fighters, as well as experimentally on other designs. It provided interceptor
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...
s with a weapon that could shoot down any bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
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 velocityMuzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
of 2000 ft/s (609.6 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 in (25 mm) of armor plate
Vehicle armour
Military vehicles are commonly armoured to withstand the impact of shrapnel, bullets, missiles, or shells, protecting the personnel inside from enemy fire. Such vehicles include tanks, aircraft, and ships....
at 500 yd (457.2 m). It was magazine-fed and could be fired manually or by remote control through a solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
mounted on the rear of the gun.
Recoil
Recoil
Recoil is the backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile and exhaust gasses, according to Newton's third law...
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
Breechblock
A breechblock is the part of the firearm action that closes the breech of a weapon at the moment of firing....
assembly. The nonrecoiling 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, ammunitionAmmunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
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.
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 3 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
AmmunitionAmmunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
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 37 mm (1.46 in) automatic gun, M4, was developed and standardized for aircraft use.
The 37 mm gun (1.46 in), M4, used the same high-explosive (M54) and practice (M55A1) projectiles as the 37 mm (1.46 in) 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 37 mm (1.46 in) armor-piercing shot, M80, was developed and standardized.
High-explosive shell, 37 mm, M54 standard
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 1.68 gr 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
Tetryl
2,4,6-Trinitrophenylmethylnitramine commonly referred to as tetryl is a sensitive explosive compound used to make detonators and explosive booster charges....
weighed 0.10 lb (45 g), and the alternate Composition "A" charge weighs 0.105 lb (48 g). The tetryl loading consisted of a 200 gr (13 g) 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 36 gr as against 23 gr for the pellet used with the tetryl load.
Practice shell, 37 mm, 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 lb (900 g), and as fired the shell weighed 1.34 lb (610 g). The 0.16 lb (70 g) charge of M2 powder was Hercules NG formula of single perforated grains with a 0.030 in (0.76 mm) web and gave the prescribed muzzle velocity of 2000 ft/s (609.6 m/s).
Armor-piercing shot, 37 mm, M80 standard
The AP shot was a monoblock 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 lb (1.05 kg), the weight of the AP shot was 1.66 lb (750 g). The propelling charge was 0.15 lb (78 g) of M2 powder of a Hercules NG formula with a single-perforated grain and 0.030 in (0.76 mm) web.
Use
The only aircraft to see service use of the M4 were the Bell P-39 Airacobra and the derivative P-63 KingcobraP-63 Kingcobra
The Bell P-63 Kingcobra was a United States fighter aircraft developed in World War II from the Bell P-39 Airacobra in an attempt to correct that aircraft's deficiencies...
, both of which saw action with the Soviet Air Forces on the Eastern Front
Eastern Front (World War II)
The Eastern Front of World War II was a theatre of World War II between the European Axis powers and co-belligerent Finland against the Soviet Union, Poland, and some other Allies which encompassed Northern, Southern and Eastern Europe from 22 June 1941 to 9 May 1945...
. The U.S did not supply M80 armor-piercing rounds for the autocannons 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 37 mm (1.46 in) automatic cannon was mounted on numerous US Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
PT boat
PT boat
PT Boats were a variety of motor torpedo boat , a small, fast vessel used by the United States Navy in World War II to attack larger surface ships. The PT boat squadrons were nicknamed "the mosquito fleet". The Japanese called them "Devil Boats".The original pre–World War I torpedo boats were...
s as deck guns, beginning with the Solomon Islands campaign
Solomon Islands campaign
The Solomon Islands campaign was a major campaign of the Pacific War of World War II. The campaign began with Japanese landings and occupation of several areas in the British Solomon Islands and Bougainville, in the Territory of New Guinea, during the first six months of 1942...
. 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 37 mm (1.46 in) 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 configurations 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.
See also
- List of U.S. Army weapons by supply catalog designation
- Nudelman-Suranov NS-37Nudelman-Suranov NS-37The Nudelman-Suranov NS-37 was a aircraft cannon, which replaced the unreliable Shpitalny Sh-37 gun. Large caliber was planned to allow destruction of both ground targets and planes .Developed by A. E. Nudelman and A...
, (Nudelman N-37Nudelman N-37The N-37 was a powerful, 37 mm aircraft cannon used by the Soviet Union. It was designed by V. Ya. Nemenov of A.E. Nudelman's OKB-16 to replace the wartime Nudelman-Suranov NS-37, entering service in 1946...
) - Vickers S gunVickers SThe Vickers Class "S" was a 40 mm cannon used to arm British aircraft for attacking ground targets in the Second World War.-History:...
- COW 37 mm gunCOW 37 mm gunThe COW 37 mm gun was a British automatic cannon that was developed as a heavy-calibre aircraft weapon.It was trialled in several installations and specified for the Westland C.O.W. Gun Fighter...
- QF 2-pounder Mark XIV
- MK 108 cannonMK 108 cannonThe MK 108 was a 30 mm caliber autocannon manufactured in Germany during World War II by Rheinmetall-Borsig for use in aircraft.-Development:...
- Bordkanone BK 37BK 37The Bordkanone BK 3,7 was a 37mm anti-tank/bomber autocannon based on the earlier 37 mm Flak 18 made by Rheinmetall. It was mounted on World War II Luftwaffe aircraft such as the anti-tank or bomber-destroyer versions of the Junkers Ju 87D-3 and G-2, Henschel Hs 129B-2/R3, Messerschmitt Bf...