37mm Gun M3

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37mm Gun M3 on Carriage M4
M3 on display at Fort Sam Houston, Texas.
Type	anti-tank gun
Place of origin	United States
Service history
Used by	US
Wars	World War II
Production history
Designed	1938
Manufacturer	Gun: Watervliet Arsenal, Carriage: Rock Island Arsenal
Produced	1940-1943
Number built	18,702
Specifications
Weight	413.68 kg
Length	3.92 m
Barrel length	overall: 2.1 m / 56.6 calibers bore: 1.98 m / 53.5 calibers
Width	1.61 m
Height	0.96 m
Crew	4-6
Shell	37x223R (Cartridge case M16)
Caliber	37 mm
Breech	vertical block
Recoil	hydrospring
Carriage	split trail
Elevation	-10° to +15°
Traverse:	60°
Rate of fire	up to 25 rounds per minute
Maximum range	6.9 km
Sights	telescopic, M6

The 37mm Gun M3 was the first dedicated anti-tank gun fielded by the US forces. Introduced in 1940, it became the standard anti-tank gun of the US infantry, until replaced in this role by more powerful 57mm Gun M1 in 1943-44. By that time, the evolution of German tanks rendered the 37 mm piece ineffective. In the Pacific, where the armor threat was less significant, the M3 remained in service until the end of the war. Like many other light anti-tank guns, the M3 was widely used as infantry support and an anti-personnel weapon, firing high-explosive and canister rounds.

In one of the tank-mounted variants (M5 or M6), the gun was used in several models of armored vehicles, most notably the Light Tank M3/M5, the Medium Tank M3 and the Light Armored Car M8. In addition, M3 in its original version was mated to a number of other self-propelled carriages.

[edit] Development history

In mid-1930s the US Army had yet to field a dedicated anti-tank gun; anti-tank companies of infantry regiments were armed with .50-cal machine guns. Although there were some considerations of replacing the MGs with more powerful weapon, only after the outbreak of the Spanish Civil War the situation started to change. The war was characterized by a growth of the tank threat, but the combat experience suggested that light anti-tank gun, such as the German PaK 35/36, gives an adequate solution.^[1]

In January 1937, inspired by reports about successful use of anti-tank guns in Spain, the Ordnance Committee recommended development of a such a weapon;^[1] two PaK 36 guns were acquired for study.^[2] The Infantry branch was chosen to oversee the work as the future main user of the weapon. The Infantry wanted a lightweight gun which could be moved around by the crew, so any ideas of using larger caliber then that of the German gun were brushed aside.^[1]

Development and testing continued until late 1938. Several variants of gun and carriage were proposed until on 15 December a combination of T10 gun and T5 carriage was officially adopted as 37mm Gun M3 and Carriage M4.^[1] Although patterned after PaK 36 and often referred to as a copy of it^[3], the M3 differed significantly from the German design, including different breech mechanism, longer barrel with different rifling, different cartridge etc..

The gun was manufactured by Watervliet Arsenal and the carriage by Rock Island Arsenal. First pieces were delivered early in 1940.^[1] The production continued until 1943.

Some minor changes in the gun construction were introduced during the production period. The carriage received modified shoulder guard and traverse controls (carriage M4A1, standardized on 29 January 1942); although Ordnance requested upgrade of all M4 carriages to M4A1, the process wasn't completed.^[1] Other change was threaded barrel end to accept a big five-port muzzle brake (gun M3A1, adopted on 5 March 1942). According to Zaloga,^[1] the latter was intended to avoid kicking too much dust under dry ground conditions; it turned out to be a safety problem when used with canister ammunition and consequently never saw combat. Other sources mention the muzzle break as intended to soften a recoil and say that it was dropped simply because additional recoil control measures weren't really needed.^[2][4]

In attempt to increase the armor penetration of the M3 several squeeze bore adapters (including the British Littlejohn adaptor) were tested; none were adopted. Experiments with rocket launchers on the M4 carriage (e.g. 4.5in rocket projector T3) also didn't produce anything practical.^[1]

[edit] Description

The barrel was of one-piece forged construction, with uniform rifling (12 grooves, right-hand twist, one turn in 25 calibers). The breech end of the barrel was screwed into a breech ring. The breech mechanism was of vertical sliding block type. The barrel was fitted with a hydrospring recoil system.^[6]

The carriage was of split trail type, with pneumatic tires.^[6] Mounted on the axle next to the wheels were the "wheel segments" - segment-shaped supports that could be lowered to provide more stability in firing position or raised so they wouldn't impede moving the gun.

The telescopic sight M6 and both elevation and traverse controls were located on the left side, so one gunner was able to aim the gun. The traverse gear had release mechanism which allowed free movement of the barrel in case quick traverse was needed.^[6]

[edit] Organization and employment

Manhandling a gun into position during a training at Fort Benning. Note the raised wheel segments.

US 37mm gun crew in combat at Saipan, 1944. From left to right are two ammunition carriers, gunner and assistant gunner. The shield is fitted with some kind of extension plate.

Under the organization active in 1941, each infantry battalion had an anti-tank platoon with three 37 mm guns and each regiment an anti-tank company with nine, totaling 18 pieces per regiment. 3/4 ton trucks were assigned as prime movers, but many units received the 1/4 ton truck (better known as the jeep) instead. Two 37mm companies were also supposed to be a part of the divisional anti-tank battalion (along with eight 75 mm guns); in December 1941 these battalions were reorganized as independent tank destroyer battalions and eventually opted for self-propelled anti-tank guns.^[7] An airborne division had 36 37 mm anti-tank guns under organization of October 1942: four in divisional artillery, eight in glider infantry regiment, 24 in AA/AT battalion.^[8]

In Marine Corps service, prior to 1943 the role of AT weapons was officially entrusted to 20 mm automatic guns in regimental and battalion weapon companies, though in practice units used the 37mm M1916 for training and were equipped with the M3 (four in each battalion and additional 12 in a regiment, in three platoons of four) before being sent to the frontline.^[9] Under the E-series Table of Organization from 15 April 1943, a marine division had a special weapons battalion with 18 37 mm guns in three batteries of six and an infantry regiment had a weapons company with 12, in three platoons of four, totaling 54 pieces per division. The F-series TO (5 May 1944) removed the special weapons battalion from the divisional organization and the G-series TO (officially from 4 September 1945, but in practice implemented late in the war for some units) reduced the weapon company to two platoons, resulting in a total of 36 and 24 pieces per division accordingly.^[10]

The M3 saw action for the first time during the defense of the Philippines in December 1941.^[7] Throughout the war it remained effective against Japanese vehicles (which were thinly armored and, moreover, were rarely committed in large groups) and its weight allowed manhandling with relative ease (e.g. when attacked by Japanese tanks on Betio, marines were able to manually heave the M3 over the five-foot-high seawall^[11]). Because of those factors, the gun remained in service with the Marine Corps until the end of the war, being employed as both an anti-tank and an infantry support piece (though in the latter role the M3 with its small high-explosive projectile was only somewhat effective); firing a canister ammunition proved useful in stopping Japanese infantry attacks. Some Army units in the Pacific also used the gun until the end of the hostilities.^[7] Unhappy with the unusually low shield of the M3, some Marine Corps units extended it to provide better protection. A standard kit was tested in 1945, but was never issued.^[12]

The experience of the North African Campaign was completely different. The gun was soon found out to be not powerful enough to deal with late production Panzer III and Panzer IV. After the nearly disastrous Battle of Kasserine Pass in February 1943, reports from some of the involved units mentioned 37 mm projectiles "bouncing off like marbles" from turret and front armor of German medium tanks and proclaimed the gun "useless unless you have gun crews with the guts to stand and shoot from 100 yards". The Army was initially uncertain if these reports reflected the obsolescence of the weapon rather than unrefined tactics and lack of experience, but on 26 May 1943 a new organization had the M3 replaced by the 57mm Gun M1 (the US-produced version of the British QF 6 pounder), with Dodge 1 1/2 ton trucks as prime movers. But only by spring 1944 did the 57mm gun reach the battlefield in large numbers.^[7]

Meanwhile, the Italian campaign was launched. On the day of the Sicily landing - 10 July 1943 - M3 guns helped to repel an attack by Italian Renault R 35 tanks, but were inefficient in a subsequent encounter with Tigers from the Herman Göring division. The Italian theater had lower priority for reequipment than Northwest Europe, and some M3s were still in use there late in 1944.^[13]

By mid-1944 the M3 fell out of favor even with airborne troops, despite their strong preference for compact and lightweight weapon systems. Although the Airborne Command rejected the 57 mm M1 in summer of 1943 claiming its unfitness for airlifting^[14], and although the organization of February 1944 still had airborne divisions keep their 37 mm guns, before the Normandy airdrops the two divisions involved - the 82nd and the 101st - were reequipped with British-manufactured 6 pounders, of a version designed to fit into the Horsa glider.^[8]

The only major lend lease recipient of the M3 was the Chinese Kuomintang Army (1,669 pieces). The gun was also supplied to Bolivia (4), Canada (3), Chile (198), Colombia (4), Cuba (1), El Salvador (9), France (130), Great Britain (78), USSR (63) and other countries (100).^[15]

While the US forces retired the gun soon after the end of the war, some nations still had the gun in service in early 1970s.^[4]

[edit] Variants

• Gun variants:
  • T3 - the first prototype.^[1]
  • T7 - a prototype with semi-automatic horizontal sliding block breech.^[2]
  • T8 - a prototype with Nordenfelt eccentric screw breech.^[2]
  • T10, standardized as M3 - an adopted version, with manual vertical block breech.^[1][2]
  • M3A1 (1942) - version with threaded barrel end to accept a muzzle break, which was never issued.^[1]
• Carriage variants:
  • T1, T1E1 - prototypes.^[1]
  • T5, standardized as M4 - first adopted version.^[1]
  • M4A1 (1942) - carriage with improved traverse controls.^[1]
  • In 1942 the Airborne Command requested a version with removable trails. A prototype was tested, but in 1943 the project was dropped as unnecessary.^[1]

[edit] Self-propelled mounts

37mm Gun M5, as mounted in Light Tank M2A4.

37mm GMC M6 with improvised machine gun mount.

Soldiers of the US 3rd Infantry on maneuvers, 1942.

Two tank gun variants were developed based on the barrel of the M3. The first, initially designated M3A1 but renamed M5 on 13 October 1939, was shortened by 5.1 inches (3.5 calibers) to avoid damage to the tube in wooden areas. Later a variant with semi-automatic breech (with empty cartridge ejection) was developed. This variant - M5E1, adopted as M6 on 14 November 1940) - received a full length barrel. The tubes were interchangeable, but replacing M5 with M6 and vice versa would result in unbalanced mount and was therefore prohibited.^[16] These guns were mounted on several models of tanks and other armored vehicles:

• Light Tank M2A4: M5 in mount M20. The recoil mechanism, protruding beyond the gun mask, had to be protected by an armored casing.^[17]
• Light Tank M3: M5 in mount M22, in late production vehicles M6 in mount M23. These mounts were fitted with more compact recoil mechanism, eliminating the need for the protective casing.^[18]
• Light Tank M3A1, M5: M6 in mount M23.^[19]
• Light Tank M3A3, M5A1: M6 in mount M44.^[19]
• Light Tank (Airborne) M22: M6 in mount M53.^[20]
• M3 series medium tanks (as a secondary weapon): M5 or M6 in mount M24.^[21]
• Heavy Tank M6 (as a secondary weapon): M6 in mount T49.^[22]
• LVT(A)-1 "amtank": M6 in mount M44.^[19]
• Light Armored Car T22 / M8 and the competing designs T21 and T23: M6.^[4]
• Armored Car M38: M6.^[23]
• Armored Car T17 and T17E1 in the "Staghound Mk I" configuration: M6.^[24]
• British Humber Armoured Car Mk IV: M6.^[25]

Versions of the gun in turret mounts were also used in the Medium Tank T5 Phase III (T3 barrel, mount T1)^[26], in the Medium Tank M2 / M2A1 (M3 barrel, M2A1: mount M19),^[27] and in the 37mm Gun Motor Carriage T42 (mount M22).^[28]

In addition, M3 in its original configuration was mated to a number of other vehicles resulting in an assortment of 37mm gun motor carriages:

• 37mm Gun Motor Carriage T2, T2E1 (Jeep).^[4]
• 37mm Gun Motor Carriage T8, T33, T44 (Ford swamp buggy).^[4]
• 37mm Gun Motor Carriage T13 (6x6 truck).^[4]
• 37mm Gun Motor Carriage T21, M4, M6 (Dodge 3/4 ton 4x4 truck).^[4]
• M29 Weasel based mount.^[4]

[edit] Ammunition

Armor penetration of the M5 was about 3 mm less at all ranges.^[19]

[edit] Gallery

Philippine Scouts at Fort McKinley firing a 37mm gun in training. Note the lowered wheel segments.

Aiming the gun (crew training, Fort Benning).

HE Mk II Shell and APC M51 Shot.

TP M51 Shot and 10-gage adapter M2.

[edit] Notes

[edit] References

• Zaloga, Steven J. and Delf, Brian - US Anti-tank Artillery 1941-45, Osprey Publishing, 2005 (New Vanguard 107), ISBN 1-84176-690-9.
• Hogg, Ian V. - Allied Artillery of World War Two - Crowood Press, Ramsbury, 1998, ISBN 1-86126-165-9.
• Chamberlain, Peter and Gander, Terry - Anti-Tank Weapons, Arco Publishing Company, New York, 1974 (WWII Fact Files), ISBN 0-668-03505-6.
• Rottman, Gordon - US Marine Corps Pacific Theater of Operations 1941-43, Osprey Publishing 2004 (Battle Orders 1), ISBN 1-84176-518-X.
• Rottman, Gordon and Chapell, Mike - The US Marine Corps 1941-45, Osprey Publishing 1995 (Elite 59), ISBN 1-85532-497-0.
• Hunnicutt, R. P. - Stuart: A History of the American Light Tank., Presidio Press 1992, ISBN 0-89141-462-2.
• Hunnicutt, R. P. - Sherman: A History of the American Medium Tank., Presidio Press 1994, ISBN 0-89141-080-5.
• Hunnicutt, R. P. - Firepower: A History of the American Heavy Tank., Presidio Press 1988, ISBN 0-89141-304-9.
• I. Moschanskiy - Armored vehicles of the Great Britain 1939-1945 part 2, Modelist-Konstruktor, Bronekollektsiya 1999-02 (И. Мощанский - Бронетанковая техника Великобритании 1939-1945 часть 2, Моделист-Конструктор, Бронеколлекция 1999-02).
• Technical Manual TM 9-2005 volume 3, Infantry and Cavalry Accompanying Weapons, War Department, 1942.
• Field Manual FM 23-81, 37-mm Gun, Tank, M6, War Department, 1942.
• History of U.S. Marine Corps Operations in World War II at "HyperWar" website
• The Marine Division and M3A1 37mm antitank Gun at "WW2Gyrene" website.
• M38 and T17 armored cars at "WWII vehicles" website.

[edit] External links

Wikimedia Commons has media related to:

M3 37 mm gun

• Photo gallery at Fightingiron.com
• Photo gallery at SVSM.org.