Saturday, 7 October 2017

Medium Tank M3

The American army had only a handful of medium tanks at the start of WWII. That does not mean that American designers ignored vehicles of this class. In the summer of 1939, the Medium Tank M2 entered production. Only 18 units were built, but it turned out to be the start of a new era for American tank building. The layout of its chassis became the foundation of American medium tanks. In 1940, the superior Medium Tank M2A1 was built, although it was already obsolete at the time. Based on that design, American engineers built the Medium Tank M3, the first mass produced American medium tank. The tank and its modifications only lasted in production for a year and a half, but its unusual looks made it a landmark of tank design. There are many opposing opinions about the tank, so let us approach it as neutrally as possible.

On a tight timeline

The history of the Medium Tank M3 began on June 13th, 1940. On that day, the Ordnance Committee developed requirements for a medium tank armed with a 75 mm gun. These requirements were composed after studying the war in France. It turned out that the Medium Tank M2A1 no longer met the requirements of modern war.

As odd as it sounds, the Americans considered the 75 mm L/24 tank gun optimal as a weapon. Its armour piercing characteristics may have been far from ideal, but the PzIV was preferred by German soldiers that had to fight alongside it. It's not surprising that the Americans considered the 75 mm caliber more promising than 37 mm.

An improved full-scale model of the Medium Tank M3. The vehicle already lost its turret with two machineguns.

At the time the requirements were composed, the Americans did not have an equivalent of the 7.5 cm KwK L/24. A satisfactory gun was quickly found. In 1937, requirements were composed for a light 75 mm AA gun. This gun was supposed to be used in places where the 76 mm AA gun was too heavy. The French M1897 field gun was used as the basis for the design. Its length was reduced to 31 calibers, the screw breech replaced with a sliding one, creating the 75 mm T6 AA gun.

Trials of this gun went poorly, and the AA gun remained experimental. In the summer of 1940, it was needed once more, but this time by tank designers. The T7 75 mm tank gun was created on its basis. Its characteristics were far more impressive than those of the German 7.5 cm KwK L/24. The closest analogue would be the Soviet L-11 gun.

Final variant of the model, approved by the start of 1941.

The biggest issue that American engineers faced was the placement of the gun in the tank. The T7 did not fit into the existing turret, but their ability to modify the tank was limited. This was because the American army desperately needed medium tanks, and any delay could mean a failure to meet deadlines.

Then, the designers remembered the Medium Tank T5E2, which was being tested in the spring of 1939. The hull gun made their task easier and reduced the amount of conversion work needed. However, the weapon design of the Medium Tank T5E2 could not be called satisfactory. The gun mount had to be redesigned. Even so, the overall concept was considered promising enough by the American military, that the tank was standardized as the Medium Tank M3 on July 11th, 1940, even before it was built.

The first experimental Medium Tank M3, built by the Rock Island Arsenal. Aberdeen Proving Grounds, late March 1941. You can see that the commander's cupola has no observation device from the left side.

The first model of the tank was presented on August 26th, 1940, at the Aberdeen Proving Grounds. The Medium Tank M3 model was significantly different from the Medium Tank M3 we know today. The chassis of the Medium Tank M2A1 was almost unchanged. The machineguns in turrets in the corners of the hull remained. A hull mount for the 75 mm T7 gun was added in the front right corner of the fighting compartment. Its firing arc was limited, but it was an improvement over the Medium Tank T5E2.

The number of machineguns in the hull did not decrease. A pair of Browning M1919 machineguns was added in the front left part of the fighting compartment. The gun in the turret remained, and a small cupola with an AA gun was added to the top. The front of the hull was now 50 mm thick, and the sides were 38 mm thick.

The same tank, demonstrated to the Ordnance Department.

The reaction of the American military to the model was mixed. The fact that a medium tank could carry a 75 mm gun was good, but the limited aiming arc was a drawback. They wanted the gun to be housed in a fully rotating turret, but there was no such turret at the time. Nevertheless, the Ordnance Committee decided that the tank was an improvement over the M2A1, and was good enough as a temporary measure. A series of 360 of these tans was proposed, during the production of which, a medium tank with a fully rotating turret and a 75 mm main gun could be built.

"Management" inspecting the tank personally.

After inspecting the model, a large number of changes was requested. The machinegun sponsons and turret were removed, limiting the machineguns to a pair fixed in the front of the hull. A radio operator was placed in the front left part of the fighting compartment instead. A large number of changes was made to the fighting compartment. This led to the creation of a second model of the Medium Tank M3. It included all of the requested changes, but was still based on the M2A1. Later, a final version of the model was built, which had a new transmission. Instead of a 5-speed gearbox, it had a 5-speed synchronized gearbox. The transmission elements were also combined into one unit, bolted to the front of the hull. The unit was composed of three parts, which were also bolted together. This layout, designed by Harry Knox, made servicing the tank easier.

The turret was also unusual. Nominally, it housed three crew members, but they occupied the turret basket underneath. It only contained all three when the commander was firing the machinegun in his cupola or when he was sitting in the turret during a march. Many parts of the tank (turret, commander's cupola, gun mount, pistol ports, transmission cover) were cast.

Cutaway diagram of the tank. As you can see, it's not that roomy on the inside.

On August 28th, 1940, an agreement was signed with the Chrysler corporation for production of 1000 Medium Tanks M3. At the same time, the order for 1000 Medium Tanks M2A1 was cancelled. The tanks would be built at the Detroit Arsenal, which Chrysler started building on September 9th, 1940.

The British were interested in the American capacity for building medium tanks. Initially, they wanted to produce Matilda infantry tanks, but it was quickly made clear that the Americans would not cooperate. An idea came up to take the Medium Tank M3 as the base, and built a British tank. This was the birth of the Grant I, or General Grant. British modifications of the Medium Tank M3 and its use in Commonwealth armies will be covered in a separate article. Here, let us only say that turrets for the British and American versions were developed in parallel.

Crew and ammunition placement diagram. The loader of the 75 mm gun was the only member of the crew who felt comfortable.

Technical documentation was mostly ready by late December of 1940. Work on armament and the turret was happening in parallel. The prototype was built by the Rock Island Arsenal. Final changes were made to the documentation in February of 1941, and the first Medium Tank M3 began its first test drive on March 13th. On March 21st, the vehicle arrived at the Aberdeen Proving Grounds, where the turret and armament were installed.

Overall, the prototype, registration number U.S.A. W-304191, was not too different from the final model, with the exception of a missing observation device from the left side of the commander's cupola. The mass of the vehicle was 27.9 tons, 1.5 times that of the Medium Tank M2A1. Many laugh at the shape of the American tank, but the Medium Tank M3 was among the best medium tanks in production at the time. It had armour which reliably protected it from the German 3.7 cm Pak, decent mobility, and powerful armament. What is most important, is that it was ready in time.

Hull and engine mixup

While the Medium Tank M3 prototype was being designed and built, the Ordnance Department corrected the production schedule. 360 or even 1000 units was no longer enough. By the end of 1940, the military's appetites grew: every day, 14.5 tanks were expected from factories, 6.5 of which were meant for the British. As production grew closer, the demands grew too: 1000 tanks per month in April, 2000 in July. The final number was even more impressive: 25,000 tanks were awaited in 1942, and 45,000 in 1943. Recall that, at some point, Tukhachevskiy's plan to build 50,000 tanks was considered madness.

The first production Medium Tank M3 during an official demonstration. Detroit Arsenal, April 24th, 1941.

For obvious reasons, plans and reality diverged. The first mass production Medium Tank M3 was completed at the Detroit Arsenal on April 24th, 1941, at which point it was triumphantly delivered to the customer. The tank confidently crossed an obstacle course and broke a thick log in front of a stunned audience.

Time was needed to set up mass production, and the Arsenal alone could not produce 1000 tanks per month. Officially, production began in June of 1941, but acceptable volumes of production were only reached towards the end of the summer. Another factory had to be pulled into the production: the American Locomotive Company (ALCo). To satisfy British requirements, two more railroad companies were included: the Pressed Steel Car Company and Pullman-Standard Car Manufacturing Company.

Assembly of tanks at the Detroit Arsenal.

Improvements to the tank began almost immediately after it was put into production. This was especially true for its armament. In the spring of 1941, work was underway to equip the tank with vertical stabilizers, and not just the 37 mm turret gun, but also the 75 mm T7, standardized under the index M2. Work on the stabilizer dragged on. Even though the decision to install it it was made in June of 1941, they were only used starting in November. It is easy to distinguish tanks with stabilizers by their counterweights. The M6 gun had a counterweight shaped like a long rod under the barrel, and the M2's counterweight was attached at the muzzle.

The presence of counterweights is a sure sign that the tank is equipped with stabilizers.

Work on an improved gun was also underway. The prospective Medium Tank T6 (later M4) would carry a 75 mm T8 gun with a 40 caliber long barrel. The installation of a more powerful gun coincided with some other changes. It turned out that the hatches on the sides were vulnerable to flanking fire. Early M3 guns were installed with tanks that had these hatches, but they were quickly welded shut. Soon after, the hatches were disposed of altogether, leaving only the pistol ports.

One of the first Medium Tanks M3 equipped with the 75 mm gun M3.

Later, the tank received improved bogeys, since its mass grew from all of these improvements. Towards the end of production, the crew was reduced from 7 to 6 men: the radio operator was removed, and his duties were partially carried out by the driver. In 1942, one of the hull machineguns was removed, and replaced with a plug. A toolbox was attached to the front of the hull. The driver received a periscopic observation device for use in combat.

The last of the Medium Tanks M3. As you can see, the hatches on the sides were removed.

In July, production of the M3 ceased. During this time, the four factories produced 4924 tanks of this type, including the Grant I. Most of these tanks were built at the Detroit Arsenal.

Medium Tank M3A1, with a noticeably different hull.

The Medium Tank M3 was not only the first American tank to be built at different factories, it was the first to be produced in many variants. This is especially true of the hull. Like many other American tanks of the time, the M3's hull was riveted. This kind of assembly was simple enough to be used at many factories, but had its drawbacks. The riveting process took a long time, and the rivets were a danger to the crew. When hit with a shell, the inner part of the rivet could chip off and turn into a deadly projectile.

The cast upper hull allowed for better use of the fighting compartment volume, but increased mass.

In June of 1941, the Ordnance Committee began a program to seek out different hull assembly methods. The first of them was casting. The upper part of the hull was cast as a single component. The side hatches became smaller. In addition to simplifying production, the cast hull allowed for more rational use of the fighting compartment volume, but increased the tank's mass to 28.6 tons.

Late production M3A1. It does not have any side hatches.

On October 9th, 1941, the M3 with a cast hull was standardized as the Medium Tank M3A1. The American Locomotive Company (ALCo) was chosen as the producer. Production began in February of 1942. It did not last long: ALCo built 300 tanks of this type before August. Unlike "regular" M3s, tanks with cast hulls were not exported. All of them were used by the American army.

As with other tanks of the M3 family, the M3A1 was initially produced with M2 guns, later replaced with the long-barrelled M3. Analogous design changes, such as elimination of the side hatches and one of the machineguns were also applied to the tank. The M3A1 also served as a test bed for the Guiberson T-1400-2 diesel engine. This air cooled radial engine achieved an output of 350 hp. The trials were disappointing, but 28 tanks were equipped with engines of this type.

Medium Tank M3A2, with a welded hull.

The second alternative to a cast hull was welding. Welded hulls were more promising than cast ones. The shape of the hull remained unchanged compared to the M3, but there was no need to drill holes in the plates for rivets. The welded connection was also stronger. Finally, the cast hull had its own drawbacks. The cast armour was weaker than the equivalent thickness of rolled steel. It's not surprising that welding became the main method of assembly for American tanks.

The M3A2 series was very small: only 12 tanks.

Development of a new modification of the Medium Tank M3 was initiated in August of 1941. The development was done at the Rock Island Arsenal. Trials showed that the idea was correct: the connections became stronger, and the tank's mass dropped to 27,400 kg. The tank was standardized as Medium Tank M3A2 before trials even began. A new factory was chosen to make it: Baldwin Locomotive Works (BLW). The first M3A2 arrived at the Aberdeen Proving Grounds by January 1st, 1942. The factory was ramping up production slowly, and only 12 tanks were delivered by March. At that point, production ceased, since one important change was made to the design.

Cutaway of the Medium Tank M3A5. The biggest change was a new engine and different rear part of the hull.

One of the most important features of the Matilda tank that the Americans took note of was the pair of diesel engines. The Americans had similar engines to offer, primarily the two-stroke air-cooled 6.98 L GM 6-71. These engines were used on "GM Old Look" busses since 1940.

These engines were important for two reasons. First of all, the issues with Guiberson radial engines demonstrated that this type of engine had no future. Second, William Knudsen, the head of the Office of Production Management, understood that there were not enough Continental R975 engines for all tanks. Finally, the GM 6-71 was a reliable and compact design, which allows a pair of them to be used easily.

The Medium Tank M3A3 had a welded hull, unlike the M3A5.

In August of 1941 work on creating an engine based on the GM 6-71 was approved. The pair of engines received the index General Motors 6046. Its nominal output was 375 hp, and maximum output was 400 hp. Medium Tank M3 with serial number 28 was used as a test bed. The mass of the tank grew to 29 tons as a result of the conversion, but the top speed grew to 48 kph. It's not surprising that the Ordnance Committee approved this engine and standardized the tank as Medium Tank M3A5 in October of 1941. These tanks can be distinguished by the reworked rear plate with a characteristic "pocket", and the addition of exhaust pipes.

Late production M3A5. The gun has a short barrel, but already has a stabilizer. The side hatches are welded shut.

Baldwin Locomotive Works was chosen to produce the M3A5, and production was set up alongside the M3A2. Another interesting fact is that another tank was accepted into service in parallel: the M3A3. This was an M3A5 with a welded hull. The M3A5 entered production earlier, in January of 1942. Overall, 591 tanks of this type were built, 185 were sent to Great Britain. As for the M3A3, these tanks entered production in March of 1942, and 322 tanks were built before December. They were also in demand by the British, who received 49 tanks.

A characteristic rear plate allows one to distinguish diesel tanks.

The introduction of the last variant of the Medium Tank M3 was also connected with the engine. Its story begins in June of 1941, when Knudsen visited Chrysler. The reason for this visit was issues with engine supplies. The required rate of production meant that there would be a shortage of Continental R975 engines. A new power plant was needed, meant primarily for Lend Lease vehicles. The automotive company decided to not reinvent the wheel, and produce an engine based on a light 6-cylinder model. The result was the most unusual tank engine of the war: the Chrysler A57 Multibank. It consisted of five engines, connected into a star shape.

Cutaway of the Medium Tank M3A4. The exhaust pipes, directed out of the upper rear plate, can be seen.

On November 15th, 1941, a tank equipped with this engine entered trials. It turned out that this strange design was more than usable. The fuel expenditure was higher than on the Continental R975, but this was a small price to pay for reliability. It is not surprising that the M3 with this engine was standardized as the Medium Tank M3A4 in December of 1941. The first mass production tank of this type began trials at the Aberdeen Proving Grounds in February of 1942. These tanks can be distinguished by the lengthened engine compartment and the exhaust pipes in the rear. Of course, the engine needed some work, but it was clear by the summer of 1942 that there was an alternative gasoline engine available.

Production Medium Tank M3A4.

The Detroit Arsenal was chosen as the producer of the Medium tank M3A4, but it didn't stay in production long. By this time, the Medium Tank T6 turned into the Medium Tank M4, and most factories changed over to producing it in the summer of 1942. It's not surprising that production of the M3A4 ceased in August. 109 tanks of this type were built, all of which had signs of late production tanks: 75 mm M3 gun, no side hatches, and stabilizers for both guns. Overall, 6258 tanks of the M3 family were built, quite a few for a "temporary measure".

First wave medium tank

The first shipments of Medium Tanks M3 began in the late summer of 1941. The military awaited these tanks with great enthusiasm, since very few American tank units had medium tanks, and even then, these were obsolete M2 and M2A1 models. Thanks to the rapid rates of production, the Medium Tank M3 began appearing frequently in photographs and on film reels. Of course, the American military understood that they need a tank with a "normal" 75 mm gun (in a rotating turret). Nevertheless, this was a sufficiently modern tank, even with the hull gun.

The tank is driving from the factory to its place of service. The armament is not yet installed.

Let us discuss the hotly debated fighting compartment, or rather, its impressive dimensions. The American designers did not intent to install a tennis court in it. The appearance of such a large fighting compartment was due to the tank's layout. A number of the crew (the 75 mm gunner and loader) had to work while standing. The fighting compartment height had to allow them to do this, which made the hull very tall. Additionally, the large fighting compartment didn't mean that there was a lot of free space inside. Only the loader of the 75 mm gun had sufficient room, and the rest of the positions were rather cramped. The rotating floor and turret basket consumed a lot of internal volume.

The turret held three crew members: the commander, gunner, and loader. The driver and radio operator sat up front. Like on the Medium Tank M2 and M2A1, the drive shaft ran between the driver's legs. Of course, the shaft was covered up, but the feeling of 350 hp spinning underneath you is a very uncomfortable one. The radio operator's experience was also far from calm. He sat on the machinegun ammunition, like a yogi. The hull machineguns to his front also didn't add to his comfort. There were some places in the tank with a lot of room, but, overall, the components were very tightly packed.

These photos were hardly a rarity. The increased mass of the new medium tanks caused bridges to break under them.

The medium tanks sat around with no purpose for the first half a year of the American participation in the war. The specifics of the Pacific theater of war mean that the Light Tank M3 was more suited for fighting there, and the medium tank would have been a hindrance. The main mission of the Medium Tank M3 was training. For this reason, the British ended up being the first to use the Medium Tank M3 in combat. The Americans kept a close eye on "their" tanks, and aided the British whenever possible.

It's difficult to overestimate the importance of the tank as a training aid. When the Medium Tank M4 became available, the Americans already had many crews that were experienced in the use of medium tanks. Considering that the M3 and M4 designs were similar in many respects, this experience was put to good use. 

Preparation for fighting in the desert, summer 1942.

By the fall of 1942, the majority of American first line units were rearmed with the Medium Tank M4A1. Nevertheless, the M3 still saw battle. It just so happened that the 1st Armoured Division, which was the first to receive medium tanks, still did not have new Medium Tanks M4A1 by the summer of 1942. Its 13th Tank Regiment had M3 tanks of various types, both with long barrelled M3 and short barrelled M2 guns. With these vehicles, the division landed at Oran on November 8th, 1942.

A late production M3, burned up during the battle for Tunis, early 1943.

The American tanks didn't have time to meet the French. The face-off between Renault D1 and Light Tanks M3 was not long. The real war began in late November, when the 1st division started fighting in Tunis. The division took heavy losses. Nevertheless, by the time the fighting in Africa ended, it still had 51 Medium Tanks M3 available. These were the main medium tanks of this unit until the end of the fighting.

Of course, the Medium Tank M4A1 was superior, but it's difficult to say that the M3 was a bad tank. The level of protection was about the same, and the difference in height was not very significant. In addition, recall that the British fought in North Africa in these tanks too, and they did not consider it a bad tank. They were replaced with the Sherman II and Sherman III at the earliest opportunity, but only because these tanks were superior. Overall, the Medium Tank M3 was an odd tank, but an effective one.

The 193rd Tank Battalion was one of the few units that used the M3 in the Pacific.

The last place where American tankers used the Medium Tank M3 was the Makin Atoll in the Pacific. The 193rd Tank Battalion stood out here. Against the Japanese, the M3s were, if not kings, then at least confident masters of the battlefield. Japanese light tanks could do very little to the M3. Theoretically, the Americans could have continued using the M3 in the Pacific, but, given the availability of the improved M4, there was no point. In April of 1944, the Medium Tank M3 was deemed obsolete. These tanks continued to fight, but as special vehicles. In other armies, they held on for significantly longer.


  1. The British weren't overly happy with the design of the M3, nor the Canadians. Part of the reason the Ram was developed. The Americans had a large order placed for Rams that the British wanted that would be acquired via lend lease. When M4 production had reached such a stage that they could met the demands for users outside of the US the order was canceled.

    Around the 1940-1941 period they were still calling it the Canadian M3, and sometimes the M4C. US tested a hull to destruction and had the pilot model shipped to them as well for testing. They compared the cast hull to a cast M3 hull.

    Ballistic tests of cast armor hulls for medium tanks M3 APG 218-9

    "Weight differences between American and Canadian hulls was not too great. Resistance to penetration of test hull was comparable to that of American hull, which was very satisfactory. Since the test hull was thicker and had more high obliquity surfaces, it was considered the test hull would yield greater protection than American design"

    1. Not like the Britishers had anything meaningfully better at the time ofc... or for that matter for pretty much the rest of the war.
      ʅ ( • ε • ) ʃ
      Far as I've read about it for their part the Germans and Italians sat up and seriously took notice when these things started turning up in North Africa. The issues stemming from the rather ad hoc layout aside it was a quite powerful tank for the period in question.

  2. The US 1st Armord Division had a mix of M4, M4A1 and M3 tanks in its medium tank companies in North Africa. It *had* been fully equipped with Shermans but some of them had been taken for shipment to the British 8th Army.

  3. The British in North Africa may not have loved the *design*, which was very obviously flawed, but they sure loved the thick armor, big gun and especially the engine that consistently worked. Three things that cannot be said of any British-manufactured tank in the desert in 1942. The M3 was the only tank in the desert that could engage German AT guns with HE until the M4 came along.