Sunday 18 December 2016

Light Tank M2: Two-Headed Light

In January of 1935, the Light Tank T2E1 arrived at Fort Benning for military trials. This vehicle was the result of nine years of trial and error, which began with the design of the Light Tank T1. Over time, the concept of the light tank changed radically. It transformed from a two man tank with an engine in the front and a 37 mm gun as the main armament to a 4 man tank with a rear engine, front transmission, and machineguns in a two man turret. As a result of the trials, the Light Tank T2E1 was accepted into service as the Light Tank M2A1.

Two Heads are Better than One

The Light Tank T2E1 gained a significant amount of weight on its way to mass production. In its initial state it weighed 6803 kg, but various changes to improve its characteristics raised its mass to 8618 kg. This was more than a ton over the limit established by the Secretary of War in the spring of 1933. However, there was nothing that could be done. The tank reached such a level of reliability that the military had to overlook that requirement.

One of the first Light Tanks M2A1. Registration numbers are not yet painted on.

The first nine Light Tanks M2A1 were built by Rock Island Arsenal in 1935. Since the prototype Light Tank T2E1 had the serial number 1, these tanks had numbers 2-10. The vehicles also received registration numbers U.S.A. W 30101–30109.

The mass production tank turned out to be a little lighter, 8523 kg, while its armour and mobility remained the same. The design included all the suggestions for improving the experimental tank made after the trials.

One of the complaints about the T2E1 was the poor visibility. This issue was solved by adding a commander's cupola. This added another problem: it was only possible to climb out of the tank through the commander's station. This issue was also present on many American light and medium tanks.

The turret changed as well. The slopes on its upper part were removed, but the front became sloped. The hull also changed somewhat. According to requirements, the mufflers were taken out of the engine compartment and placed outside. Another change was the appearance of a radio station with an antenna port in the left rear part of the hull roof.

T7 combined machinegun mount used on the tank.

There were no changes in armament. Two machineguns, one 12.7 mm and one 7.62 mm, were placed in the combined T7 mount, which was protected with a gun mantlet from the outside. This armament was sufficient for fighting armoured cars and most tanks of the time.

It must be said that while experimental T2 light tanks were designed with armament in mind, it was never installed. It was also never installed on some Light Tanks M2A1: a portion of the tanks were used almost until the very end of their service with no guns. In order to train crews, the primary purpose of this tank, weapons weren't needed.

M2A1 on exercises. This tank has no turret armament.

The armament was one of the reasons why only 9 Light Tanks M2A1 were made. The standardized vehicle inherited one drawback from the Light Tank T2 that was almost impossible to correct. The drive shaft, covered with a casing, was placed very high up and interfered with the the crew when the turret turned. The problem could be solved, but American engineers decided to forego trying to lower the shaft with complex mechanisms. The path they took was simple.

In order to solve the problem of the shaft, the designers looked to the Vickers Mk.E, which in many ways was the inspiration when the Light Tank T2 was built. This time, the Americans decided to borrow the idea of two one man turrets. It's worth noting that the Vickers Mk.E Type A had two turrets for a completely different reason. It needed them to perform the function of a trench sweeper. The Americans were more interested in the crew's comfort. The idea of two turrets was first tried on the light cavalry tank Combat Car T5, where it achieved satisfactory results.

Experimental Light Tank T2E2.

In the same year of 1935, another experimental tank entered trials, the Light Tank T2E2. It had no serious changes to the chassis compared to the Light Tank M2A1. The turret platform roof was replaced, and two one man turrets were installed instead of one two man. The commander's turret was very similar to the Light Tank M2A1's turret. It had the Browning M2HB machinegun on the M9 mount. The right turret, a little smaller in size, had the Browning M1919A3 machinegun in the M12E1 mount. Both machineguns had telescopic sights.

The antenna port was moved to the center of the hull roof, behind the turrets. This solution was also copied from the Vickers Mk.E Type A.

On trials, the tank with registration number U.S.A. W.30114 showed satisfactory results. The mass grew to 8660 kg, which had almost no impact on mobility. The addition of a second turret meant that the mobility of fire increased radically. The purpose wasn't to clear trenches, as the theater of war the light tanks were meant for had few of them. However, cavalry was still a popular type of force at the time, and the ability to shoot at more than one target was not considered excessive.

The antenna mount is visible in this photo. Without thinking too hard, the Americans borrowed it from the Vickers Mk.E.

The Light Tank T2E2 was accepted into service almost at the same time as the Light Tank M2A1. The new tank received the index Light Tank M2A2. 9 tanks were built in 1935 with serial numbers 11-19 and registration numbers U.S.A. W.30110–30119.

Over the course of comparative trials, it became obvious that the layout with two one man turrets is better. The American infantry received a vehicle with good maneuverability of fire, which was very suitable for raids like the hunt for Pancho Villa. With the same armament as the Medium Tank T4 and better maneuverability, the Light Tank M2A2 cost half as much. It's not surprising that after the comparative trials, the tank was selected for mass production in large numbers in 1936.

Backbone of the Pre-War Force

1936 was a busy year for the Rock Island Arsenal. The American army ordered 125 Light Tanks M2A2, serial numbers 20-144. Tanks haven't been ordered in these volumes since WWI. A year later, another order for 104 tanks was made. The tanks received registration numbers U.S.A W.30120-30368.

Three tanks built in 1937 were equipped with Guiberson T-1020 diesel engines. Like the stock Continental W-670, the engine had its roots in the aircraft industry and was air cooled. Compared to the aircraft A-1020 variant, its power was reduced from 340 to 250 hp. The tanks equipped with diesel engines were indexed Light Tank M2A2E1. Military use of tanks with diesel engines showed that they are difficult to start in cold weather.

Personnel of the 11th Tank Regiment with their vehicles.

Mass production finally allowed infantry units to start rearming with new tanks. The Light Tank M2A2 became a symbol of the American army in the late 1930s. These tanks were often seen in newspapers and on newsreels. The completely obsolete M1917 Light Tanks were finally replaced.

Aside from the continental US, these tanks also served in Hawaii. The Pearl Harbour naval base was housed on Oahu island since 1908, and the Schofield Barracks army base was not far from there. The 11th Tank Regiment located at Schofield Barracks initially had M1917 Light Tanks. This unit as also rearmed with Light Tanks M2A2, and reports of this unit's exercises were a common sight in American media.

Combined training of tankers and engineers together was common as well. This training consisted both of tankers learning to cross obstacles and engineers learning to create impassable obstacles for tanks. The new tanks were kept busy.

The last Light Tank M2A2 with serial number 248 and registration number U.S.A. W.30368 was sent to the Aberdeen Proving Grounds in July of 1937. The tank was indexed Light Tank M2A2E2, and was noticeably different from its comrades. The thickness of its armour was increased to 25 mm, and its mass grew to 9675 kg. The engine compartment was also changed. This tank became a test bench for various technical solutions that were used in the improvement of the experimental T5 Medium Tank.

Light Tank M2A2E2 in its initial configuration at the Aberdeen Proving Grounds, August 1937.

In August of 1938, the tank returned to Rock Island, where it was subjected to another series of changes. A new engine and suspension were tested simultaneously. Unlike the previous design, the bogeys remained the same, but the idler was completely changed. It was increased in diameter and lowered to the ground, increasing the track's contact surface. This was done for a good reason: the Light Tank M2A2, as well as other tanks of that family, was tall and shallow, leading it to oscillate lengthwise.

The modernized tank used the 6-cylinder General Motors 6-71 engine. This 7 L 188 hp diesel engine, unlike the Guiberson T-1020, was water cooled. The new engine required more space in the engine compartment, which lengthened the tank.

During trials, the bogeys were widened in order to increase the contact surface, and connected with a reinforcing beam.

Trials of this tank, indexed Light Tank M2A2E3, began in early July of 1939. As a result of these changes, the tank's mass reached 10.5 tons. As a result, neither the engine nor the new suspension were put into mass production, but the trials were not conducted in vain. Later, a duo of General Motors 6-71 engines was used in American medium tanks, and the slightly changed idler was used on the Combat Car M2 and Light Tank M3.

Light Tank M2A2E3 on trials. The lengthening of the rear part of the tank led to changes of its suspension.

Further development of the M2 light tank family went, oddly enough, along the lines of making tanks for cavalry. In the summer of 1937, the Combat Car M1E2 entered trials. Its greatest difference from the predecessor was an altered suspension with greater distance between bogeys. These changes increased the contact surface length from 2184 mm to 2464 mm, increasing the stability of the tank. The hull was also converted. The engine compartment was changed especially thoroughly, and the access to the engine was notably improved. The vehicle went into production under the index Combat Car M1A1.

Light Tank M2A3. The changes in the turrets and engine compartment are visible.

The military made a sensible decision to take the Combat Car M1E2 and make an infantry tank based on that design. This led to the creation of the Light Tank M2A3. Unlike the cavalry tank, which had one two man turret, the infantry tank had two one man turrets. The turrets were simplified compared to the M2A2: there were no more curved plates, and the turrets were assembled from only flat plates/

Like previous vehicles, the Light Tank M2A3 was assembled with rivets. Since the rivets had flat heads, they are very hard to see, and it creates an illusion of welding on photographs. In reality, welding was used on American tanks much later.

The combat weight of the tank grew to 9450 kg, and the top speed decreased to 58 kph. On the other hand, the thickness of the front armour of the hull and turret grew to 22 mm. This was the result of studying battles in Spain, which showed that tanks need to be reliably protected from  high caliber machineguns. 

The diesel version, M2A3E1, can be differentiated by the longer ducts leading to the air filters.

The first Light Tanks M2A3 began entering service in the summer of 1938. In total, the Rock Island Arsenal built 73 of these tanks. The tanks received serial numbers 249-321 and registration numbers U.S.A. W.30368-30441. The tanks used 250 hp Continental W-670 series 9 engines. In addition, 8 tanks indexed Light Tank M2A3E1 received Guiberson T-1020 series 3 diesel engines, later replaced with the series 4.

Timken electric transmission.

During service, the gearboxed with sliding gears were replaced by gearboxes with synchronizers. The Light Tank M2A3 was the first American tank on which an electric transmission was used. One of the mass production tanks was converted to use a transmission designed by the Timken company. Two electric motors and other equipment were placed at the front of the tank. The electric transmission took up more space than the stock one. Because of that, the M2A3E2 tank that received it remained an experiment. Nevertheless, American engineers returned to the idea of an electric transmission several times.

Light Tank M2A3E3 on trials, January of 1941. The rear of the hull and suspension were changed radially.

Even though the Guiberson T-1020 engines didn't show themselves exceptionally well, the American military didn't give up on trying to install diesel engines into their tanks. On February 21st, 1940, the Ordnance Corps approved the installation of a V-shaped 4 cylinder V-4-223 diesel engine produced by General Motors in a Light Tank M2A3.

This work was done less to improve the M2A3, and more to modernize the Light Tank M2A4. The engine compartment of the tank was altered to be like that of the M2A4. The 250 hp diesel fit into the compartment, but it was heavier, forcing the installation of a larger idler to increase the contact surface of the track, like on the Light Tank M2A2E3.

The V-4-223 diesel engine.

The converted tank, indexed M2A3E3, entered trials in January of 1941. The changes increased its mass to 10,800 kg. As a result of trials, the engine was still not accepted for use in light tanks. On the other hand, the suspension used on the Light Tank M2A3E3 migrated without almost any changes to the production Light Tank M3.

First Antarctic Tank

Unlike the Light Tank M2A4, its younger brothers never got to fight. The American military soberly evaluated the abilities of their machinegun tanks. On the other hand, it's difficult to say that the Americans weren't ready for war while looking at the M2 series of light tanks. These tanks were built for a theater of war different from the European one, and were very well adapted for it. By September 1st, 1939, the American army had a little under 450 modern light tanks armed with high caliber machineguns which easily penetrated bulletproof armour.

The concept of light and fast vehicles was popular in many countries. For instance, the backbone of the British army in September of 1939 was 1002 Light Tanks Mk.VI, which was inferior to the American tank in all respects. The characteristics of the American tanks were closer to those of the German Pz.Kpfw.II tanks, slightly inferior in firepower and superior in mobility. As of September 1st, the PzII composed over 40% of the German tank fleet. Another 38% was made up of Pz.Kpfw.I tanks, which had no chance in battle with American tanks.

Light Tank M2A3 during obstacle training, Fort Belvoir, April 1942.

The American light machinegun tanks were used for training duties. Numerous exercises held since the end of the 1930s were performed with these tanks. The M2 family remained in service until 1942. Even though they did not fight, they served an important purpose. They became learning tools for thousands of American tankers. The Light Tank M2A1 was also the starting point for the T5 medium tank, which later turned into the Medium Tank M2.

Time and duty took their toll. Not a single M2A1 survived, and one M2A2 and M2A3 remain in museums. Another Light Tank M2A2E3 also survives to this day.

The tale of this tank could end here, if not for one "but". The history of the Light Tank M2A2 contains one forgotten episode that makes its career unique. This was the first, and so far the last, tank used in the Antarctic. This happened in 1939, which Admiral Richard Byrd began his third expedition. Officially, it was called the United States Antarctic Service Expedition. It was made famous by the Snow Cruiser, an enormous, progressive, and largely useless vehicle that became stuck 150 km along the route. Of course, that story is just one of many from the expedition. Its main task was the creation of an eastern base on Stonington Island in Marguerite Bay and a western base ("Little America") on the Ross Ice Shelf. That is where three Light Tanks M2A2 were sent.

Light Tank M2A2 on Stonington Island. A T3E4 Tracked Light Tractor can be seen in the background.

Even before being sent to the Antarctic, the tank was lightened, the armament and a portion of the armour removed. It quickly became obvious that this was not enough. Turrets were also removed from the tanks, the ground pressure was decreased, but use of the tanks showed that it was necessary to reduce the weight by another third. The turrets didn't go to waste: they were used to make the tracks wider and let the tanks drive better on loose snow. In order to prevent the tank from being covered in snow that was kicked up, extended fenders were attached to the front.

The use of the tank in low temperatures also resulted in a lot of hassle. Nevertheless, the tanks were actively used on both bases to tow sleds. During one outing, a tank managed to travel 50 km with a 2 ton sled at second gear. The tanks were not returned to the United States. To this day, a Light Tank M2A2 remains at Stonington Island.

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