37mm Gun M3 anti-tank gun

The 37mm Gun M3 anti-tank gun was the first dedicated anti-tank gun to enter service with the US Army, and remained an effective weapon in the Far East throughout the Second World War, although was quickly provided to be obsolete against the Germans after its combat debut in Tunisia in late 1942-early 1943.

For most of the interwar period the US army relied on normal artillery and the 12.7mm Browning MG as anti-tank weapons, both of which could penetrate the thin armour used on most tanks of the period. However by the mid 1930s better armoured tanks were entering service. US liaison officers operating in Spain reported that the new German Rheinmetall 37mm Pak 36 was an effective anti-tank weapon.

37mm Antitank Gun M3A1 on Okinawa

In January 1937 the Ordnance Committee recommended that work should begin on a new 37mm anti-tank gun and an example of the German gun should be purchased. However the Infantry, Cavalry and Artillery all had different ideas about the type of gun required. A conference was held in May 1937 to try and come to some agreement. It was agreed to base the new gun on the PaK 36. The Infantry were placed in charge of the project as they would be using the new weapon. Authority to build pilot models of a 37mm Gun T3 and Gun Carriage T1 was granted on 9 September 1937.

There were still some disagreements between the Infantry and Artillery branches, in particular over the gun carriage. The Infantry wanted the gun to be useable by a single gunner, the Artillery wanted a two-man crew. As a result a second carriage, the T1E1, was also developed, which used a crew of two and could be trained more quickly. Some Ordnance officers wanted a larger gun – the Soviets were already using 45mm anti-tank guns, but the Infantry wanted the gun to be light enough to be moved by a four man crew.

The T3 gun and T1 carriage underwent trials in February-March 1938 and didn’t impress. The carriage was unstable, the gun had a poor breech design and the ammo performed badly. A new T5 carriage was developed, which solved the carriage problems. Four new gun designs were produced. Trials of the new variants were carried out in the summer of 1938 and the T10 gun and T5 carriage was accepted for production. On 15 December 1938 they were approved as the 37mm M3 gun and M4 carriage.

Like the German original the 37mm M3 was a low weapon, about the height of a seated man. The original version had a traversing hand wheel (similar to on field guns), and a traverse-release handle which allowed the gunner to move the gun manually. It used a hydrospring recoil system and a drop block breech.

The M3 entered production in the winter of 1940, with the gun being built at the Watervliet arsenal and carriages at the Rock Island arsenal. 2,000 were built in 1941. After the attack on Pearl Harbor President Roosevelt ordered production of anti-tank guns to reach 18,900 per year by the end of 1943.

A total of 18,702 37mm guns were built, making it the most numerous American towed anti-tank gun of the war. Production peaked in 1942 when 11,812 were built, but that declined to 4,298 in 1943 when production ended.

Variants

Carriage M4A1

The original traversing system was felt to be too slow for use against fast moving targets. To improve the speed the gun could be traversed the Carriage M4A1 was developed. This had a new shoulder guard for the gunner, combined with a clutch to allow free traversing. This allowed the gunner to easily disengage the traversing mechanism and push the gun around with his arm or shoulder. The M4A1 was standardised on 29 January 1942 and became the most numerous version of the gun.

37mm M3A1 Gun

One problem with the very low profile of the gun was that it could thrown up clouds of dust when fired in dry conditions. In an attempt to fix this problem the gun was given a gas deflector based on that developed by the Swiss Solothurn company. Threading was cut into the mouth of the barrel to allow the gas deflector to be screwed in. However it soon became clear that the new deflector couldn’t be used safely with canister ammo, so it was never used in combat. It was approved on 5 March 1942 and its use cancelled on 28 January 1943.

Combat

The 37mm anti-tank gun began to replace the .50in heavy machine guns as the anti-tank weapons in US infantry divisions in 1941. Each battalion was given one anti-tank platoon with three guns, and each infantry regiment had an anti-tank company with nine guns, giving a three battalion strong regiment 18 guns. They were meant to use ¾ ton trucks as prime movers, but many regiments got lighter jeeps instead.

The 37mm gun entered combat in the Pacific. It was first used on the Philippines in December 1941 but little is known about its performance there. Nearly a year later it went to Guadalcanal with the Marines. The Japanese didn’t deploy many tanks to Guadalcanal, and the ones they did send were the Type 97 Chi-ha medium tank. The 37mm gun was more than capable of dealing with this tank. In October 1942 the Japanese 1st Independent Tank Company attempted to attack across the Matanikau river and lost most of its tanks to 37mm fire. When no Japanese tanks were present the 37mm was light enough to move relatively easily through the jungle, making it a useful artillery piece. It could be used as a bunker buster, while its canister ammunition was a useful defensive weapon.

The 37mm M3 remained in use throughout the war in the Pacific. The US Marines continued to use it to the end of the war. Some US Army divisions moved onto the 57mm Gun M1 in 1944 but others retained the lighter 37mm gun. Although the Japanese did develop more heavily armoured tanks most of those vehicles remained on the Home Islands, so the tanks encountered elsewhere in the Pacific tended to be older models that were still vulnerable to the 37mm gun.

Against the Germans the picture was rather different. The 37mm gun made its combat debut during the fighting in Tunisia in late 1942-early 1943. It was quickly shown to be obsolete. Both the Panzer III and Panzer IV had been up-armoured and the 37mm gun could only penetrate their frontal armour at very close range. It was also much smaller than the standard German and British anti-tank guns, the 50mm PaK 38 and 6-pdr respectively. At the Kasserine Pass Rommel claimed to have captured or destroyed 67 anti-tank guns. Observers from the Army Ground Force reported that commanders on the ground condemned the gun as useless and recommended discarding it. Tests against a captured Panzer III carried out in Tunisia in the spring of 1943 showed that it could penetrate the front turret armour at 300 yards and the hull sides at 600 yards, but not the front hull armour. General Thomas Lewis from the Artillery considered it to be a ‘very effective anti-tank weapon’ and blamed the troops for using it wrong. However the same report found that the 57mm gun was effective against all German medium tanks at 1,000 yards. The Army Ground Force realised that the 37mm gun was obsolete and in May 1943 officially replaced the nine regimental guns with nine 57mm guns. However production of the new gun took some time to get up to speed, and large numbers of them didn’t enter combat until the spring of 1944, by which time the US army was fighting in Italy.

The 37mm gun saw combat during the invasion of Sicily. In the early fighting the 37mm proved that it could cope with older tanks, helping fight off an Italian attack using captured Renault R-35 tanks, but was useless against the Tiger. However the Italian campaign had a lower priority for new equipment than the forces being gathered for Normandy, so the 37mm remained in combat well into 1944. It was still the most common type when the Americans landed at Salerno, and it wasn’t until the summer of 1944 that the 57mm gun outnumbered it. A total of 167 37mm guns were lost during the fighting in Italy.

A number of 37mm guns were still in use with infantry divisions on D-Day, but they were quickly withdrawn after the first clashes with German armour proved they were entirely ineffective.

Books,
Zaloga, Steven J., US Anti-tank Artillery 1941-45

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