The Ordnance Department gave its permission to produce the British QF 6-pounder under license in February of 1941 in order to supply them through Lend Lease. At that point, only prototypes of the gun had been built. Even though the 6-pounder was ready for production in the summer of 1940, the British decided to postpone it for mass production of 40 mm QF 2-pounder guns. This was a logical decision. The British needed to rapidly compensate for the armament lost in France, and six 2-pounders could be made for the cost of one 6-pounder.
Production of the QF 6-pounder in Britain began only in November of 1941, and even then, in a simplified form. The Mk.II gun had a 43 caliber barrel instead of 50 caliber. This restriction was imposed by British industrial capabilities. The Americans, on the other hand, had no such issues, and so they decided to produce the Mk.I with a 50 caliber barrel. This gun was standardized as the Limited Standard 57 mm Gun M1 on Carriage M1. Soon after, the carriage was improved with wheels and suspension of the American type. This carriage received the index M1A1. The index of the gun did not change. The M1A2 carriage with free traverse was produced after September 1942, on British initiative. This carriage allowed the gunner to disconnect the regular traverse mechanism and aim the gun using a shoulder stock, which made it easier to track moving targets.
For the US Army
Having agreed to produce the weapon for foreign needs, the Ordnance Department proposed that a similar weapon should be developed for the American army. The Infantry Department was not a fan of the idea, as they considered that a 57 mm gun would be too heavy to push around the battlefield using only the crew's power. Development of a domestic 57 mm gun, the T2, began anyway in May of 1942. Four prototypes were built. They had a similar barrel and breech to the British weapon, used the same ammunition, but had a different carriage. Two of the guns received hydropneumatic recoil mechanisms from the 75 mm infantry howitzer, two others received springs. The American T1 carriage was wider and more stable than the British one. However, comparative trials performed in 1942 didn't show any noticeable advantage over the M1, which was already in production: 3877 of these guns were produced in 1942. The only thing left to do was to convince the infantry.
The 57 mm Gun M1.
The ill-fated 57 mm Gun T1.
The infantry insisted on keeping the 37 mm M3 gun, considering mobility on the battlefield more important than penetration. The M1 weighed three times as much: 1239 kg vs 414 kg. Only the encounters with German tanks in Tunisia convinced the Infantry Department to change their minds. Shipments of M1 guns on M1A3 carriages began in the spring of 1943. These guns had an American type tow hook, which was tougher and more suitable for towing the guns off-road. Production of guns on the M1A2 carriage for Lend Lease proceeded in parallel. The M2 carriage that made transporting the gun easier entered production in 1944. This carriage had a deployable wheel on the right trail. Finally, the M2A1 carriage was introduced towards the end of production in 1945. It had an improved elevation mechanism. The index of the gun on all of these carriages remained M1.
M1 gun on the M2 carriage.
Only AP ammunition was produced until the end of the summer of 1944. This was the M70 shot with a core of high toughness steel, without an explosive charge (mass 2.85 kg, muzzle velocity 853 m/s) and the M85 shell with a ballistic cap and 42 g of explosives (3.3 kg, 823 m/s). Shipments of British HE ammunition were rare. This made it hard to use the 57 mm guns in support of infantry. Delivery of M303 HE ammunition (2.99 kg, 703 g of explosive, 823 m/s muzzle velocity) began in late summer of 1944. Finally, the M305 canister shot was introduced in January of 1945, which was quite effective against personnel at short range.
The penetration characteristics of the gun weren't bad. At 90 degrees, the M70 penetrated 135 mm of armour from 100 meters, 112 from 500 meters, 89 mm from 1000 meters, and 70 mm at 1500 meters. At two kilometers it could penetrate 55 mm of armour. The M85 had poorer penetration at short range, but better at long range: 73 mm at 1500 meters and 64 mm at 2000 meters.
In total, the USA produced 15,637 M1 guns (3877 in 1942, 5856 in 1943, 3902 in 1944, 2002 in 1945). More than a third (5352) were sent as a part of Lend Lease aid: 4242 to Great Britain, 653 to France, 400 to the USSR, 57 to Brazil. The gun was also installed on the GMC T48 (known as the SU-57 in the USSR). The history of these SPGs is best saved for another article.
Service and combat
The introduction of the M1 gun in the US Army started with some difficulty. While the infantry agreed reluctantly, the cavalry absolutely refused, considering them too heavy. The Airborne tested these guns in the summer of 1943 and also rejected them.
The M1 guns were introduced into the TO&E on May 26th, 1943. Each regiment's anti-tank gun company had 9 M1 guns instead of 12 37 mm M3 guns, arranged into three platoons of three guns each. The company also had a mine platoon with a bazooka in the HQ section. 1.5 ton Dodge WC62 or WC63 trucks were used as tractors. The infantry battalion had an anti-tank platoon in its HQ, consisting of three M1 guns. Like in the anti-tank company, each platoon had three Bazookas and three 12.7 mm machineguns. Instead of 24 M3 guns, each regiment now had 18 M1 guns, and each division had 54 guns.
M1 guns from the 34th Infantry Division on parade. July 4th, 1943, Rabat, Morocco. Since the Dodges hadn't arrived yet, the guns are towed by M3 APCs.
The guns made their debut in 1943, during the Sicilian campaign. Since the 37 mm guns had not yet been entirely replaced, the Americans could compare how the two guns fared in combat. The results were mixed. General Patton wrote:
"If a more powerful round can be produced for the 37 mm gun, then it would be preferable to the 57 mm gun on the offensive. It can be towed by a low 1/4 ton truck, while the 57 mm gun needs a halftrack or a 3/4 ton truck with a high silhouette. Unlike the 37 mm gun, the 57 mm gun can't be moved by the crew off-road."
The greatest complaint about the M1 was still the same: excess weight. The crew was the same as for the M3 gun, five men (commander, gunner, loader, two ammunition carriers). On the other hand, the only armour that was impenetrable for the 57 mm gun was the front of the Tiger and Panther tanks. Their sides could be penetrated from 1000-1200 meters. The first 76.2 mm M5 anti-tank guns weighing 2 tons appeared in Italy in October of 1943, and the M1 suddenly didn't seem so heavy. However, the M5 wasn't used by infantry divisions, but separate anti-tank battalions.
Field manual FM-7-35 " Infantry: Antitank Company, Infantry Regiment And Antitank Platoon, Infantry Battalion" was issued on March 15th, 1944, based on the results of combat in Italy. It prescribed opening fire at tanks with the M1 gun from 750 meters. It also stated that tanks rarely fire on the move and try to find a place to stop where at least the hull was covered. When taking up positions, the commander of the platoon had to pick a place where these dead zones were eliminated. It was advised that the guns should fire as soon as the tanks stop. Knowing of American tactics, the enemy would be motivated to resume movement as fast as possible, which would no doubt reflect on their shooting.
The 57 mm guns had not forced out the 37 mm guns entirely in Italy, but the M1 was the most numerous. 37 mm guns in this region were only preserved above authorized strength. Many commanders kept them around "just in case" when they re-armed.
In the first month of fighting in Normandy, tank encounters were rare. The M1 was usually used as infantry support. Their effectiveness was limited due to a lack of proper shells. One battalion commander wrote:
"We desperately needed HE-frag ammunition for our 57 mm. They were the only weapon the infantry regiment had with a flat trajectory, but the British were the only source of ammunition. Due to a lack of tanks and commonly encountered bunkers, the 57 mm gun was not used frequently."
The first effective use of the M1 in its primary role was recorded on July 11-12th, near Sainte-Mère-Église and Carentan, where the American positions were attacked by the Panzer Lehr division. The anti-tank platoon of the 2nd Battalion of the 39th Infantry Regiment managed to hold the enemy back with the help of some bazooka teams until the 899th Tank Destroyer Battalion armed with M10 tank destroyers arrived. The Americans destroyed 16 PzIV and Panther tanks. The effectiveness of the M1 supported by bazookas was confirmed in August at Avranches, where the 9th and 30th Infantry Divisions were subjected to large scale tank attacks.
M1 crew from the 41st Motorized Infantry Regiment, 2nd Armored Division. Normandy, late July 1944. This unit received camouflage uniforms, but they were retracted in August because of their similarity to SS uniforms.
An M1 gun concealed using field expedient means. 9th Infantry Division, August 1944.
M1 gun in a French town. September 1944.
Further combat in Normandy showed that the complaints about the M1's weight were overstated. The crew could move the gun on their own for short distances if the ground was not too soaked with rain. It was easy to hide the 57 mm guns in bocage country, and transporting the guns was not as hard as 76.2 mm guns.
M1 gun in bocage country.
A gun crew is unhooking their M1 gun from an M2A1 halftrack. Aachen, October 15th, 1944.
Supplies of 57 mm HE began to reach units in August of 1944. According to reports, these rounds only made up 20% of ammunition issued to gun crews until February of 1945, the rest were armour piercing. A small amount of British APCR ammunition was included along with the standard M70 and M85. These rounds could penetrate 160 mm of armour at 500 meters. However, this didn't help in the Ardennes, where the guns received the reputation of "tank bait". Lieutenant Colonel McKinley, the commander of the 1st Battalion of the 9th Infantry Regiment, lost half of his men in these battles, and declared that:
"The 57 mm gun has no place in an infantry battalion. They cannot be delivered to where they are needed. In the last operation, they could not be moved on muddied roads."
A crew from the 26th Infantry Regiment, 1st Infantry Division, in the mud of the Ardennes. December 17th, 1944.
Losses of M1 guns in the American 1st Army reached 26% in December of 1944 (compared to monthly losses of 6-8% in Normandy). There was a direct correlation with mobility: the heavier 76.2 mm M5 gun suffered 35% losses.
The 57 mm guns were chiefly used as infantry support guns in the final months of the war in Europe, as the Germans only used tanks episodically. Some regiments turned their anti-tank gun companies into ordinary infantry companies, others sent the 57 mm guns into storage, replacing them with bazookas. The finale of the was in Europe was not kind to 57 mm guns. In February of 1945 the decision was made to replace these guns in regimental companies with 17 T26E1 tanks per company.
The M1 was used in homeopathic doses in the Pacific. Only 250 guns were sent here, a tiny drop compared to the thousands sent to Europe. The ability to move guns by hand was even more valuable here, and the 37 mm guns were just fine at dealing with thinly armoured Japanese tanks.
M1 crew from the 152nd Infantry Regiment, 38th Infantry Division, in combat at Luson, May 11th, 1945.
The guns left the scene quickly after WWII. The 75 mm M20 recoilless gun replaced them as the battalion level anti-tank gun. The new regimental anti-tank company TO&E, established on June 1st, 1945, allowed for 9 tanks or SPGs: M36, M4 with a 76 mm gun, or M18. The introduction of heavy tanks into regiments was cancelled, instead they were gathered into a battalion at the divisional level. Nevertheless, some amount of M1 guns still took part in the Korean War.
Both American and South Korean forces used 57 mm guns in the Korean War.