Friday 7 April 2017

Medium Tank M2: Last Place in the Arms Race

The late 1930s were a time when armoured vehicles were developing rapidly. The start of WWII in September of 1939 gave an even bigger push to the flywheel of progress. Designs that were considered revolutionary suddenly fell behind. There were cases where tanks became obsolete soon after coming out of the factory. The American Medium Tank M2 is among those unlucky ones. You can read a lot of mockery of the combat abilities of this tank, but they are unreasonable. American engineers made a decent medium tank, but by the time it entered mass production there were already other tanks with more armour and better armament.

Turret and Casemate

The American infantry adopted the Convertible Medium Tank T4 in 1935. The Rock Island Arsenal in Davenport built 16 tanks of this type, as well as three Convertible Medium Tank T4E1, which had a casemate with machineguns on all sides instead of a turret. The tank turned out to be controversial.

On one hand, this was the first American medium tank with more than 10 vehicles produced. On the other hand, the tank had strange characteristics. Even on wheels, the tank was less mobile than the Light Tank M2A1, even thought it had analogous armour and armament. Since the Convertible Medium Tank T4 cost twice as much as its light brother, it's easy to understand the hesitation of the American military. Unlike the Light Tank M2A1 and the Combat Car M1, this tank was not developed further. It was obvious that a new tank is needed.

In addition to the war between purely tracked and convertible drive lobbies, there was another fierce battle raging on in the Ordnance Department about how to place a tank's armament. The Convertible Medium Tank T4 and Combat Car T5 existed in two variants (with a turret and with a casemate) for a good reason. Infantry captain George H. Rarey tried to get the two sides to get along. In April of 1934, he designed a concept of a convertible drive medium tank that combined the "machinegun hedgehog" and a turret with 360 degree rotation. The perimeter of the fighting compartment was lined with machinegun sponsons, and a turret with a 47 mm gun was placed in the center. The driver was placed in a separate cabin.

Captain Rarey's convertible drive tank, April 1934

The tank was never built. Trials in the 67th regiment where the Light Tank M2A1 and Convertible Tank T4 ended up showed that Harry Knox's suspension was better. However, Rarey's design was not a waste of paper.

He worked at the experimental directorate at Fort Benning. When the Ordnance Committee decided to launch work on the Medium Tank T5, the work was largely controlled by the experimental directorate. Even though the Light Tank M2 was taken as the starting point, the fighting compartment and driver's compartment migrated to this project from Rarey's tank.

This is what the Medium tank T5 looked like during initial trials.

The need to use the Light Tank M2 design when creating the Medium Tank T5 was taken literally. Many components were taken without changes to speed up the design process, such as the Continental R-670-3 engine, gearbox, drive sprockets, road wheels, idlers, and tracks. The suspension couldn't be copied exactly and had to be reinforced. Since the overall length of the vehicle titled Medium Tank T5 Phase I grew to almost one meter, the number of road wheels was increased to six.

The overall layout of the Light Tank M2 remained, but the driver was moved to the middle. As a result, the drive shaft ended up right between his legs.

Rarey's turret and gun mount design, which later was used to develop a new turret for the Medium Tank T5.

The usage of existing components helped out with the rate of development. The American engineers had to hurry; the growing tensions in Europe after the Nazis came to power were felt even across the ocean. American cavalry began receiving a new generation of light tanks in 1936. Work on new types of armament, including anti-tank, also continued.

The American military understood that a war can't be fought with light tanks alone, so the development of a medium tank remained a high priority. So high, that the tank that entered trials on November 16th, 1937, was still half a model. Its fighting compartment, turret, and armament were all made of wood. The customers cared more about how the suspension would work. Nevertheless, Rarey's concept was clearly visible in the design. The turret from his project migrated tot his tank with very few changes.

The biggest difference was the armament. The Ordnance Department understood that the 47 mm gun was too weak and ordered another gun, a 37 mm one. This was the tank version of an anti-tank gun developed by Gladeon Barnes and inspired by the 3.7 cm Pak. The result was the most powerful 37 mm gun, but when the new medium tank prototype was being tested, it was still in development.

The radically redesigned Medium Tank T5 Stage I, February of 1938. In addition to the redesigned top, you can see new cooling fins around the final drives.

The tank returned to the Rock Island Arsenal after trials, which lasted until December 29th, 1937. Improvements to the chassis were made. Since the mass of the vehicle increased to 13.5 tons, the stress on the gearbox increased by 1.5 times. It could still do its job, but the final drives overheated, and so special cooling fins were added.

Everything above the chassis was completely replaced. The tank started looking even more like Rarey's concept. Since the original turret was uninhabited (the gunner sat below), and the new requirements had to make it fit two crewmen, Rarey designed a new turret. The turret became larger and its sides became sloped.  A hatch was added to the rear. The turret armour was welded.

The driver in the tank felt like a king. The only problem was the driveshaft between his legs.

The driver's compartment also changed. It received sloped armour and three observation hatches, which provided excellent visibility when open. The fighting compartment also changed, but the concept of machinegun sponsons in the corners remained. The engine compartment shape changed as well.

Since the vehicle was experimental, mild steel was used in its construction. The thickness of the front was as high as 25 mm, which offered reliable protection against high caliber machineguns.

The Medium Tank T5 Stage I in its final form. The idea of dual 37 mm guns was later rejected.

The vehicle, numbered U.S.A. W-30369, returned from trials on February 16th, 1938. The tank reached a top speed of 49.6 kph, which was sufficient for a medium tank. Since work on armament continued, the turret housed a dummy gun. Later, it was replaced by a pair of M2A1 37 mm guns, but the dual gun design did not progress past the experiment stage. Special armour plates were added to the rear, which functioned as deflectors. The tank's machinegunners could use them to send bullets to dead zones in the case that enemy infantry got right up against the tank.

Overall, the military was satisfied with the Medium Tank T5. After Aberdeen trials, the tank was sent to Fort Benning to be tested by tankers from the 67th regiment. It was obvious that the new vehicle was superior to the Combat Car T4. With comparable mobility, the Medium Tank T5 had better protection, firepower, and crew comfort. It is not surprising that the Committee ordered that the tank be standardized under the index Medium Tank M2. As for the first prototype, it is still present at the National Infantry Museum at Fort Benning.

Gaining Weight

The verdict that the Medium Tank T5 will be adopted into service did not mean that work on it was done. Development continued, since trials revealed more than just its positive sides. The suspension had to be reinforce, the engine and transmission redone, and the armour improved. The new mass limit was 20 short tons (18.4 metric tons).

Medium tank T5 Phase III, November of 1939. The changes are not visible from this angle, but this tank was radically altered.

In November of 1938, a new tank called Medium Tank T5 Phase III entered trials. This was the second experimental prototype, the tank called Phase II was never built. The tank looked like its predecessor, but this was misleading. The tank designers jumped the gun, and the tank grew to 19 metric tons. For starters, the side armour was thickened.

The engine compartment was changed, as well as the muffler with deflector plates.

The engine group was changed completely. A much more powerful and much larger 9 cylinder Wright R-975 Whirlwind engine was used. The aircraft version produced 400 hp, but the tank version was dialed down to 346 hp. The new engine increased the top speed of the tank to 52.6 kph.

The transmission also had to be changed. A new gearbox was installed, and new final drives were used. The drive shaft in the middle forced the driver to move to the left. his place was taken up by machineguns. The drive sprocket design was changed, and the track links were widened from 295 to 406 mm.

The idea of an offset driver's cabin and a removable plate around the front machineguns was controversial.

The turret was also noticeably changed. It was now cast, its sides up to 25 mm thick. An AA machinegun was attached to the right side. The biggest change was the use of the 37 mm T3 anti-tank gun. The gun was installed with almost no changes compared to the towed gun. An armoured mantlet was added to protect from bullets and shell fragments.

37 mm T3 gun, which had almost no changes compared to the towed weapon.

Trials not only showed better mobility, but significant increase in fuel consumption. If the T5 Phase I could travel for 200 km on one load of fuel, the T5 Phase III could only drive for 168 km, and that's with bigger fuel tanks. A solution to this problem was the installation of a diesel Guiberson aircraft engine. It was star-shaped and had air cooling, just like the Wright R-975. The conversion was approved on September 20th, 1938, and the tank was renamed to Medium Tank T5E1.

Medium Tank T5E2, seen from the right.

Bigger changes were made in the spring of 1939. The offset driver's cabin gave the idea of installing something bigger in the front hull. A converted tank, named Medium Tank T5E2, entered trials on April 20th, 1939. Its main turret was replaced with the commander's turret from the Light Tank M2A3, equipped with a rangefinder. The 75 mm Pack Howitzer M1A1 was installed in te hull. The mount as the same as the one used on the light Howitzer Motor Carriage T3.

The howitzer looked natural, like the tank was designed for it.

While working with the howitzer in the small SPG was a pain, there was no such issue in the larger fighting compartment. However, the machinegun in the front right corner had to go. Trials continued on the Aberdeen Proving Grounds until February 8th, 1940, and concluded with positive results. Later experiments with the Medium Tank T5E2 directly influenced the American medium tank program, leading it away from worldwide tendencies.

Unlike with the Gun Motor Carriage T3, there were no problems with insufficient space.

Preparations for mass production of the Medium Tank M2 were underway at the same time as the experiments with the Medium Tank T5E2. The Rock Island Arsenal was chosen as the producer. The first tank with registration number U.S.A. E-30444 left Davenport in the summer of 1939. It included fixes to the defects discovered in the second experimental vehicle.

The mass of the tank was reduced to 17.3 tons, which improved the power to weight ratio. The top speed of the tank was reduced to 42 kph. The reduction of speed and engine RPM allowed an increase in fuel economy to 208 km per load. Since the final drives overheated a little, the cooling fins returned.

The designers also restored the driver's cabin and the original location of the machineguns. The width of the track links was reduced to 337 mm, and the bogeys were reinforced. The armour was also changed: the front was thickened to 28.5 mm, and the thickness of the sides was increased.

The first Medium Tank M2 on a demonstration, Aberdeen Proving Grounds, fall of 1939.

The turret and armament were changed yet again. The overall layout was the same as on the T5 Phase III, but the design was riveted, not cast. The 37 mm gun remained, now standardized under the index M3. It was installed in a new mount with a coaxial Browning M1919A4 machinegun. The tank had eight of those machineguns in total: two in the front, four in sponsons, one coaxial, and one AA.

Copy of the factory blueprint. You can see how the AA machinegun was carried on the turret.

According to the first order, Rock Island Arsenal would build 18 Medium Tanks M2 in 1939. The second production tank was sent to the Aberdeen Proving Grounds and became a test lab. Thanks to this, the tank survived to this day, albeit in a somewhat altered state. 54 more vehicles were expected to be built in 1940, but the external political situation started changing, and with it, the plans of American military minds.

Small Batch

The war in Europe was closely watched by the Americans. Just like in WWI, the US kept to a policy of neutrality, but they understood that it would not last for long. American intelligence carefully analyzed information received from Poland in the fall of 1939, and that information also influenced the development of the Medium Tank M2. Reports about the use of the Medium Tank M2 also came back from the army, and they were carefully studied.

Second mass production Medium Tank M2. Aberdeen Proving Grounds, August 1939.

One of the deficiencies with the new tank was in regards to its turret. The sloped armour "ate up" a lot of its volume. All conical turrets suffered from this. A new turret was hurriedly designed. Its base was the same as on the M2, but the sides were installed at a right angle. The rear hatch was also removed, replaced with a large single hatch in the roof.

The new turret received a modernized gun mount, called 37 mm Gun Mount M19. This mount was also developed for the Light Tank M2A4. The gunner received the ability to aim the gun horizontally without turning the turret. The experimental mount was installed on the second mass production Medium Tank M2, and trials proved that it was a good design.

The seventh mass produced Medium Tank M2 during exercises. This tank, just like the second one, became a test lab.

The next step was improvement in protection. It turned out that the pistol port shutters were vulnerable, and a proposal was made to replace them. Fighting in Poland also proved that the side armour has to be stronger, since penetrations through the side were a common occurrence.

A column of Medium Tanks M2 from the 67th Infantry Regiment, 1940. These tanks were included in the 2nd Armoured Division in July of 1940.

The result of all these changes was a modernized tank, indexed Medium Tank M2A1. It had a 400 hp Continental R-975E-C2 engine, which was a licensed copy of the Wright R-975. The mass grew to 18.7 tons, and the suspension had to be modernized. The width of the track links was also increased to 362 mm. The top speed remained at the level of the Medium Tank M2. The transmission was also changed: it received hydraulic controls, which made the driver's job easier.

The second Medium Tank M2 witha  new turret. The tank survived until today in this form.

Aside from the new turret, the Medium Tank M2A1 had novelties that were not so obvious visually. The M19 gun mount received improved armour for the gun's recoil mechanisms. The protection of the sponson machineguns also increased, and the front plate received deflectors. The thickness of the side armour grew to 32 mm, so shooting at the tank with autocannons was a pointless exercise. The front armour was not reinforced, as it was already enough. All observation hatches were improved. Now they had their fittings on the inside and were much more reliable. 

Mass production Medium Tank M2A1, Aberdeen Proving Grounds, September of 1940

The situation in Europe was taking an unpleasant course. Despite their neutrality, the US helped out France. For example, the American Curtiss Hawk 75 was the second most numerous fighter in the French air force. Trucks and other military supplies were sent en masse. On May 10th, 1940, the Germans began their push through the Benelux countries and ended up in France within the week. By the end of the month, it was clear that France would not last long. The British also took a beating, losing most of their Expeditionary Corps.

The positional scenario of WWI did not repeat itself. The biggest issue with producing the necessary number of tanks that was required in this situation was that the biggest producer of tanks was the Rock Island Arsenal, who also produced artillery.

The changes noticeably improved the crew's working conditions.

On May 29th, 1940, President Roosevelt appointed William Knudsen, the head of the automotive giant General Motors, to the post of the Head of the Office of Production Management, which organized military production. The choice was obvious. Knudsen was the man who implemented the assembly line, first at Ford, then at Chevrolet.

Knudsen quickly found his bearings and called Kaufman Keller, the President of the Chrysler Corporation, to a meeting on June 7th. They knew each other well, since Keller worked at General Motors for a long time. There was no talk of competition; WWII was raging on, and there was no guessing when the United States would become involved. The biggest issue came from the fact that the US Army only had 18 modern medium tanks at the time. As for the Medium Tank M2A1, the Rock Island Arsenal was still working on the first three tanks.

Wooden model of the hull and turret built from Rock Island Arsenal blueprints at Chrysler.

Knudsen's proposal was simple: Chrysler Corporation had to build a tank factory. Keller agreed, and a complete set of technical documentation arrived in Detroit on June 17th. Chrysler built a wooden model using the blueprints. A contract to build a tank factory was signed with Chrysler on August 15th, 1940. At the same time, an agreement was made to build 1000 Medium Tanks M2A1. The first three tanks were due in September of 1941, and production gradually increased to 100 tanks per month. The last tanks were expected in August of 1942.

Mass production of Medium Tanks M2A1 at the Rock Island Arsenal, late 1940. You can see that the arsenal had to build several types of tanks at once, and that's not including artillery.

Plans to build one thousand Medium Tanks M2A1 did not last long. The American military studied information coming from France very carefully. It was clear that the main enemy of Allied tanks would be the Pz.Kpfw.IV. The short barreled 75 mm gun was particularly impressive to the Americans. The fact that it had very limited penetration was not obvious.

Nevertheless, the new tank took shape on June 13th, 1940. The Medium Tank M2A1 chassis had no alternatives. since building a tank from scratch meant wasting precious time. The military demanded that the new tank have better armour and a 75 mm gun. That is how the Medium Tank M3 was born.

Medium Tanks M2A1 from the 2nd Armoured Division headed for exercises, June 14th, 1941.

On August 28th, 1940, the order for 1000 Medium Tanks M2A1 was officially cancelled and replaced with a contract to produce Medium Tanks M3. However, the contract with the Rock Island Arsenal was not cancelled so that its production facilities were kept busy. An agreement was made for 126 tanks of that type, which were ready by December of 1940. The production rate gradually decreased, since the Medium Tank M3 was in higher demand. The last M2A1 were delivered in August of 1941, with Medium Tanks M3 built in parallel. In total, the US Army received 84 M2A1 medium tanks.

Applique armour developed for the Medium Tank M2A1. Weighing the pros and cons, this modernization was cancelled.

It's hard to say that the Medium Tank M2A1 was bad. The Americans built an adequate fighting machine that was no worse than the PzIII Ausf. E, and was far superior to British pre-war cruiser tanks. The Medium Tank M2 also served as a platform for American medium tanks and SPGs of the wartime era. The problem with the M2A1 was that the American military evaluated its potential very soberly and decided to use a good tank to build a better one. Their motivation was correct.

As for the M2 family, the tanks served, but as training vehicles. There was, however, an attempt at improving their armour. Applique armour that raised the M2A1's protection to 76 mm was developed. Its mass increased by 4.3 tons. 

Experimental E2 flamethrower, summer of 1942.

The last attempt to send the Medium Tank M2 into battle happened in the summer of 1942. The tank was equipped with an E2 flamethrower instead of the gun. Trials showed that the range of the flamethower was small and the tank lost the ability to fire its gun at a long range. Experiments continued on the Medium Tank M3, but with similar results. These experiments were not fruitless, as the experience was used to install a flamethrower on the Light Tank M3A1.

As for the original Medium Tanks M2 and M2A1, they were used for training purposes until the end of 1942. Time was not kind to them: only one Medium Tank M2A1 remains to this day. in Fort Benning, but its gun mount was replaced with a later one.

1 comment:

  1. Great article. Thank you for translating the original.