Categories
WW2 US Medium Tanks

Medium Tanks M2, M2A1 and T5

USA (1939-45)
Medium Tank M2 – 18 built, M2A1 – 94 built (T5 – 2 built)

Having failed repeatedly throughout the 1920s and 1930s to design a new medium tank for the armed forces, the US Army decided to start over with a new design. It tried to move away from the convertible tank designs that had failed previously and do a clean slate design, leading to the T5 Medium Tank that would become the developmental ancestor of the famous M4 Sherman.

T5 Phase 1. The turret and superstructure are wooden
T5 Phase 1. The turret and superstructure are wooden (Photo: Hunnicutt’s Sherman)

Development and Testing

After encountering constant problems with trying to design an acceptable convertible tank for the Army during the 1930s, the US Ordnance board decided on May 21st 1936 to start anew and that a new design idea was needed. Designated the T5, this new medium tank was essentially an enlarged version of the already successful M2 Light Tank. As a result, this design looked radically different from the previous ones. It was to reuse as many components from the M2 as possible, namely the same engine, a similar transmission, and the same suspension. The main difference was to be the T5’s increased armor and firepower. The main design limitation was a 15 ton weight limit so as to allow it to go over the bridges found on most primary US highways. The first pilot designed to this specification was then designated as the T5 Phase I.

T5 Phase 1. A dummy 37 mm has been installed.
T5 Phase 1. A dummy 37 mm has been installed. Also, note the wheels on the upper track, these would be removed later on (Photo: Hunnicutt’s Sherman)

For armament, there were two arrangements under consideration. The first had the main weapon mounted in a 360-degree traverse turret, as was the case on the failed T4 Medium Tank. The 2nd was to have the main armament carried in a barbette or essentially casemated in the hull, in an arrangement like that of the T4E1.

As early as 1934, Captain George H. Rarey* had proposed a combination of both in a design based on the earlier Christie chassis. This idea was liked but a few more changes would need to be made. In order to stay in line with the intended role of infantry support, it was decided to mount 4 machine guns in rotors mounted in the sponsons at the corners of the fighting compartment, and to have the main armament mounted in a turret above all of this, much like the 1934 turret design. This arrangement was then finally adopted for the T5, although one difference was that the original design had the 2 forward .30 caliber machine guns mounted in auxiliary turrets rather than in the sponsons. Additionally, 2 .30 calibers were added in the hull for the driver to use with an additional provision made for anti-aircraft mounts for two more additional machine guns. The turret was also designed to carry the new high velocity 37 mm then in development, however, this gun was not available when the tank was delivered in its final state for trials in 1938. In its place, 2 older 37 mm cannons were installed to mimic the higher recoil of the new 37 mm, with the intention being to later replace them with the single high velocity 37 mm for further tests. However, this was seemingly never done as the surviving T5 today still has both 37 mm cannons.

*Captain H. Rarey (1881-1954) was a US Infantry Captain. He is little known today, but he co-authored a book ‘The Fighting Tanks 1916-1933’ and wrote a few pieces in magazines like ‘The Coastal Artillery Journal’ about tanks. and had numerous patents pertaining to tanks or weapon mountings.

T4 Medium tank
T4 Medium tank (Photo: AGF Board)
T4E1 showing the casemated weapons
T4E1 showing the casemated weapons (Photo: AGF Board)
George H. Rarey and Sereno E. Bretts early 1934 turret design
George H. Rarey and Sereno E. Bretts early 1934 turret design that would later be utilized on the T5 in a modified form (Photo: US Patent Office)
George H. Rarey and Sereno E. Bretts early 1934 turret design
George H. Rarey and Sereno E. Bretts early 1934 turret design that would later be utilized on the T5 in a modified form (Photo: US Patent Office)
Another of his patents for the turret design
Another of his patents for the turret design, this one pertaining to the gun mounting. (Photo: US Patent office)

Some other minor changes done during this development stage was to move the driver’s seat from the floor on the front left side of the tank to a position in the center over the transmission, as seen in the final design.

With its crew of 5 and armor protection ranging from 1 inch (25 mm) to ¼ inches (6.35 mm), the T5 Phase I fully loaded had a weight of just over 15 tons with a ground pressure of 9.6 psi (66.1 kPa). The tank was powered by the same 268 hp Continental air-cooled petrol radial engine as on the M2 Light Tank. The transmission had 5 speeds forward and 1-speed reverse. The suspension was likewise the same Vertical Volute Spring Suspension (VVSS) as on the M2 Light Tank. With a 16 hp/ton ratio, the top speed was a respectable 31 mph (49 kph). With its fuel capacity of 125 US gallons (473 liters) the tank had a 125 mile (201 km) range.

The first stage of testing on what was to become the M2 took place from November 16th to December 29th, 1937. The turret was not available for these tests and they were done instead with a wooden turret and superstructure which looked drastically different from the final design. Early in 1938, the metal turret was installed but the tank still carried the dummy gun. Additionally, soft steel was used here instead of a proper armor plate, so no ballistic tests could be done. The tank was then shipped to Aberdeen Proving Ground on February 16th, 1938.

T5 Phase I forward view.
T5 Phase I forward view. The metal turret has been installed but the tank still carries the dummy gun (Photo: Hunnicutt’s Sherman)

During testing both in 1937 and later at Aberdeen, a number of small modifications were made. One of these was the installation of bullet deflectors to both sides of the rear plate. The idea with these was that the plates could deflect fire from the rear machine guns into the blind area behind the tank or into any hole or trench the tank crossed. Around this time, there was also a proposed T5 Phase II, which would have been Phase I but with a different engine, although this was not built.

Overall though, the results of these tests were deemed satisfactory, and the T5 Phase I was adopted with some further changes for standardization as the M2 in June 1938. While it had been accepted, the US was actively watching the events in the Spanish Civil War, events which had implied to the US that the new German 37 mm Pak-36 anti-tank gun would be the M2’s primary anti-tank threat, and the armor was deemed not suitable to resist that gun at most anticipated ranges. Seeing this, it was decided to increase the maximum weight to 20 tons to facilitate an increase in the armor, and to test this, a new pilot vehicle with thicker armor was made, which was designated as the T5 Phase III.

The most obvious visual change from the Phase I to the Phase III was that the driver’s position was moved from the center to the left side, this gave the tank an obvious asymmetrical design.

T5 Phase III showing the asymmetrical design
T5 Phase III showing the asymmetrical design. (Photo: Hunnicutt’s Sherman)

Other modifications from the Phase I included the design for the VVSS suspension being modified by moving the return track rollers from the side to the top of each bogie. Brackets were also added connecting each bogie frame to the sponson on the center and rear bogies of each track. The principal armament was to remain the same, but the high velocity 37 mm was now installed in a cast turret, whereas previously this had been a welded turret.

Additionally, the armor was increased to 1-7/16th inches (~36 mm) thick on the turret and just over an inch (>25 mm) on the hull. With these design changes and increased armor, the tank’s new weight was 20 tons, and the original 286 hp engine was now insufficient. Accordingly, it was replaced with a Wright air-cooled radial engine. This was a 9 cylinder petrol engine which was supposed to produce 400 hp but which actually only delivered 346 hp in actual use. With a final weight of 21 tons, the design now had a 14 hp/ton ratio. The maximum speed was raised to 32.9 mph (52.9 kph) but the range dropped to only 103 miles (165 km) despite increasing the fuel tank capacity to 132 US gallons (499 liters).

Due to the higher weight, it was needed to install larger tracks, as the ground pressure was now higher, at 12.2 psi (84.1 kPa). Following a test program from November to December 1938, it was decided that, despite considerable work being needed for the controlled differential steering system, the tank was satisfactory for service, although now one-ton overweight. Oddly, unlike the Phase I, which was almost directly adopted as the M2 with few modifications, the T5 Phase III would not directly be adopted, but some of its improvements would end up finding their way into the M2A1, Most noticeable amongst these were thicker armor and a redesigned turret, although the M2A1’s turret production technique was still the same as the original M2s.

T5 Phase III side view
T5 Phase III side view, note the rear bogie clamp and the machine gun on the turret. (Photo: Hunnicutt’s Sherman)
Rear view of the T5 Phase III
Rear view of the T5 Phase III showing the rear deflector plates for the machine guns. (Photo: Hunnicutt’s Sherman)

Additionally, there was a project to mount a 75mm to the tank, designated the T5E2, but that is beyond the scope of the M2 project. Lastly, there was an additional design modification to fit a new air-cooled diesel radial engine that had been designed. This engine, the Guiberson air-cooled petrol engine, was seen as an attractive alternative engine design, as it actually made a proper 400 hp. It was recommended for installation in Phase III with the designation being the T5E1. The ultimate fate of this project is not entirely known. It was tested in this configuration but that is all that is available. However, we can assume that, as the engine and indeed the T5E1 were never standardized, it is likely that it was canceled at a later date. It is possible that the later T5E2 project kept the engine from the earlier E1, as they were built from the same tank, but this is speculation.

Standardization and Production

As standardized, the M2 had few differences from the T5 Phase I. It now had the intended 37 mm high-velocity gun, and all of the machine guns were retained. As a result of the changes, its weight had increased now to 19 tons when loaded, and the original Continental engine now resulted in the tank being underpowered, so it was replaced with a Wright 350 hp R-975 radial petrol engine. An order for 18 was placed in 1939 at Rock Island Arsenal. An additional 54 were ordered in 1940, but this order was canceled following the improvement programs. For the M2A1, the most obvious visual difference was the larger turret and the installation of pistol ports. Beyond that, M2A1’s primary difference lay in its higher power engine. The R-975, as installed on the M2, was a disappointment, making only 350 hp out of the expected 400 hp. On the M2A1, a supercharger was added, which increased engine power to 400 hp. Additionally, it had thicker armor and numerous other small modifications, which made it heavier at 23.5 tons.

Production M2, note the turret size.
Production M2, note the turret size. (Photo: British and American Tanks of World War 2)
M2A1 medium tanks on maneuvers in 1941.
M2A1 medium tanks on maneuvers in 1941. (Photo: US Army Signal Corps)

The M2A1 was intended to supersede the M2 in production and it did, but the rapidly changing situation in Europe caused plans to change. The present war situation in Europe, especially the sudden fall of France and evacuation at Dunkirk, awakened the US to the ability of its armed forces to rapidly procure what would be needed in a war. Namely, it showed that the existing facilities were far too limited. Prior to this, much of the US heavy equipment would be built in state arsenals, with all tanks being done at Rock Island. The US realized its entire tank force of 400 tanks had just 18 tanks that could be considered modern medium tanks. With the number of tanks needed, Rock Island did not have the capacity to build enough vehicles. The original plan for this was to contract locomotive and railway car companies to do this work, as they would have experience in heavy machinery. This would prove to be correct during the war, however, it was also believed that there was massive potential for mass production in the car industry that could also be applied to the issue of mass-producing tanks.

To address this, a meeting was arranged for June 9th, 1940 in Detroit between the then President of Chrysler, K.T. Keller, and William S. Knudsen. Knudsen had been the former President of General Motors and was now in charge of directing military construction. Straight to the point, he simply asked if Chrysler would be willing to produce tanks for the Army. Chrysler agreed, and plans were quickly put to work.

After a group from Chrysler headed out to Washington on the 11th to talk to Army Ordnance about it, they asked to see the tank, as they had not seen what they were expected to build, as Washington had none to show them. They were directed to Rock Island Arsenal in Illinois to view one of the pilot M2A1s under production there and it was this tank that the US Army wanted 1,500 of and which General Wesson estimated would take 2 years to do. The Chrysler party had hoped to take back the 186 pounds (84 kg) set of blueprints needed to make the vehicle back to Detroit with them, however, they could only get a few back initially, with the rest arriving there on June 17th. That night, a specially chosen group, the nucleus of the new tank arsenal, started to work in secret on the top floor of the Dodge Conant building to produce an estimate which would be ready in just four and a half weeks and would include the costs of making the tank in quantities, land, building, and the machinery required. Tanks produced by Rock Island Arsenal were made by tool room methods and some of the Rock Island blueprints were in 1/8th scale and not 1 to 1 scale. To ensure that they could grasp the size of every tank piece and build it properly, they decided to make an exact mockup of an M2A1 out of wood. The pattern shops were instructed to drill all holes and to shellac the finished model. The purpose of the shellac was simple, first, it protected the wood, and secondly if any part of the model had been improperly made or not adjusted when fitted the shellac would scrape away. When finished, this model was guarded zealously and very few knew what the men on the top floor were up to.

Wooden M2 mock-up made by Chrysler
Wooden M2 mock-up made by Chrysler to confirm the accuracy of the blueprints sent to them (Photo: Hunnicutt’s Sherman)

While the Chrysler Party now knew that they could accurately make the tank, the issue of where to build them still remained, as the USA was not yet at war and all of the existing Chrysler facilities were still hard at work building cars for the masses. The Army did not have a lot of money at this time to spend on tanks and wanted to spend them on tanks, not building new factories to make them. This had caused them to propose creating not just a factory that would be disposed of post-contract, like many of the factories that had been raised in World War 1 to fill contracts given, but instead to create a permanent tank arsenal. This was accepted as long as the army was able to find the money.

On July 17th, a month after receiving the blueprints, a total cost estimate was finished. It was based upon a factory output of 10 tanks a day and having its own armor plate machining equipment. This was not feasible with the Army’s existing funds, so the Army cut the capacity to 5 tanks per day and with no armor machining equipment, as that could be left to the mills to do.

After refiguring the plans for the new factory costs, Chrysler had a letter of intent to make 1,000 tanks by August 1942 with the Government paying for the land and plant, leasing it to Chrysler who would superintend the construction and provide the equipment for it. The fixed price for each of the M2A1s was US$33,500, a fixed price bid that was protected by an escalator clause against raising labor and material costs. This plant was to be ready by September 15th, 1941 with production to raise from three tanks in the 12th month to 100 in the 15th and thereafter through 23 months.

The factory was to be built on a site of 113 acres (45.7 hectares) some 17 miles (27 km) from downtown Detroit. This was a rural area with no public transportation, but all this would be worked out in time. While all this was happening, an important realization was reached. The M2A1 was not suitable for modern conflicts. Instead, Chrysler was to build M3 tanks in place of the M2A1 contract. While Chrysler was not to make any M2A1s and despite the M2A1 being seen as outdated, it still had merit for a modern training tank and so Rock Island Arsenal would be put to work on a contract for 126 M2A1 tanks. Production started in December 1940 and continued until August 1941, by which time production of the M3 had commenced and was ramping up. The contract for the M2A1s was then canceled with 94 already finished.

M3 mockup next to the M2A1 f
M3 mock-up next to the M2A1 from which it was derived. Note the similarity of the differential and final drive. (Photo: Hunnicutt’s Sherman)

Operational Service

Ultimately the M2’s service career was doomed to be short-lived and limited. The tanks proved invaluable in the training role, giving US tank recruits a far more modern training tank than the previous and obsolete Mark VIII tanks. But this was also the extent of the type’s service life.

M2 of 1st Armored Division on maneuvers at Fort Knox 1941. (Photo: M3 Lee/Grant Medium Tank 1941-45)
M2 Serial no 2 with the initial M2A1 turret design
M2 Serial no 2 with the initial M2A1 turret design. Note that the pistol ports have no covers. ( Photo: Hunnicutt’s Sherman)
Note the redesigned turret and redesigned pistol ports
Note the redesigned turret and redesigned pistol ports on the turret. (Photo: Hunnicutt’s Sherman)
Top-down view of the M2A1 showing its turret.
Top-down view of the M2A1 showing its turret. The hole is there to permit the use of signal flags (Photo: Hunnicutt’s Sherman)

Test Vehicles

Despite quickly being superseded by the M3 design, the basic M2 design was used for a few experimental vehicles, such as the M2 with the E2 Flame Gun. The M2 with the E2 Flame Gun was a test vehicle made in 1941 that had a flamethrower mounted where the 37 mm gun had been with the fuel containers carried on the rear of the hull. Additionally, an M2 was also used to test the British version of M3 Medium Tank’s 37 mm turret in November 1940 during the M3’s development. Unfortunately, the test results are not known.

M2 Medium with the British version of the M3 turret installed
M2 Medium with the British version of the M3 turret installed (Photo: British and American Tanks of World War 2)

Armament

The armament on these tanks was the same 37 mm M3 anti-tank gun the infantry used, just that it was the tank version of it which had a shorter barrel and was suited for tank mounting. Due to the reduced barrel length, the velocity dropped from 2,900 fps (884 m/s) to 2,600 fps (792 m/s) when firing armor-piercing (AP) ammunition. This gun fired AP as well as a small explosive charge HE round. The AP round could penetrate 53 mm (2.1 inches) of homogeneous steel armor at 500 yards (457 m) at 30 degrees obliquity and 46 mm (1.8 inches) of face hardened armor at the same range. The tank carried 200 rounds of 37 mm ammunition. Additionally, the tank carried no less than 6 M1919 .30 caliber machine guns and could carry 2 more in anti-aircraft mounts for a total of 8 machine guns. Total ammunition carried for this impressive and equally silly amount of machine guns was an equally impressive 12,250 rounds.

The reasoning behind having such high amounts of machine guns was simple. At the time of its design, medium tanks in the US Army were employed not as tanks properly, but as infantry support weapons. To this end, the 4 rotor machine guns and the 2 fixed hull machine guns would have greatly helped it in that. The 2 anti-aircraft MGs would have been of very limited value for this, however, as they required one of the hull MG gunners to open the roof hatch and stand up to use them. Indeed, a lingering part of this trend can be seen in both the M3 and early M4 Shermans still having the dual fixed hull machine guns on them.

Armor

The armor of the adopted M2 and M2A1 tanks different from that of the T5 Phase I and Phase III tanks. The M2 and M2A1’s armor was made up of Face Hardened plates, the hull was of partially riveted and partially welded construction with the turret being welded on the M2 and M2A1. The thickness of the hull on the M2 ranged from 1 1/8th inch (28.5 mm) on the front of the differential housing to just 1/4th inches (6.35 mm) on the hull floor. The top plate of the hull was 3/8th inches (9.5 mm) thick and was made of structural steel. On the M2A1, this protection was reinforced with all vertical surfaces being increased to 1 1/4th inch (31.8 mm). An additional program was also set up to increase the M2A1’s armor to a maximum thickness of 3 inches (76 mm) via 9,500 lbs (4,309 kg) of homogeneous armor. This was, however, not carried out in light of the tank’s already obsolescent state, only existing in the form of wooden armor mockups.

Wooden mock-up for the M2A1 add on armor
Wooden mock-up for the M2A1 add on armor. This was not carried out (Photo Hunnicutt’s Sherman)

Engine

The M2 and M2A1 both used the Wright Radial R975 9 cylinder radial petrol engine. However, this engine on the M2 only generated 350 hp while on the M2A1 a supercharger was added increasing horsepower to 400 p. Maximum speed on both was 30 mph (48 kph) with a top speed of 17.2 mph (27.6 kph) cross country.

Running Gear

The running gear consisted of Vertical Volute Spring Suspension, the M2 utilized 13 inches (330mm) wide tracks, the M2A1’s tracks were 14 inches (355 mm) wide in an attempt to keep the ground pressure down.

Crew

The M2 and M2A1 both had crews of 6 men – 4 gunners, a commander in the turret, and the driver in the hull.

Fate

Ultimately, all of the M2 and M2A1s produced were retired in 1945, made redundant as training vehicles by the large surplus of many other tanks with the war over. Of the 112 produced and both T5 prototypes, only 3 of the vehicles are known to survive today. At the time of writing, the original T5 Phase I prototype with its twin 37 mm armament, as well as an M2A1, are being stored at the U.S. Army Armor & Cavalry Collection at Fort Benning, Georgia. There is also an M2 hull with an M2A1 turret that is stored at the US Ordnance Museum at Fort Lee, Virginia. Interestingly, this tank which is serial no 2, has the early test version of the M2A1 turret design and features the early pistol ports which were later changed.

Legacy

While the M2 might have been obsolete when designed and built, it had a long impact on US tank design and industry. The M3 would itself be derived from the M2 Medium, and by extension, the M4 owes its lineage to the M2 medium. Perhaps the biggest impact it had was in the Detroit Tank Arsenal which was originally built to produce it, as it would go on to be expanded during the war and produce a staggering 22,234 tanks as well as rebuild some 2,825 more over the course of 1941-45. In addition to producing M3 Medium, M4 Medium, and M26 Heavy Tanks, it would later produce M46, M47, M48, M60, and M1 Abrams tanks before finally closing in 1996.

M2 Medium Tank early
Early production M2 medium tank. Notice the two extra turret mounts. The total was a staggering 9 Browning M1919 cal.30 (7.62 mm) machine guns. However, there were only four gunners manning the entire arsenal, including two for the main M3 37 mm (1.46 in) gun. The M3 light tank, of the same era, was also heavily armed with machine guns. But these features quickly lost favor.
M2A1 Medium
M2A1, the main production series, made at Rock Island Arsenal. This is the “Glamorous Gladis”, from a training unit in early 1941, now preserved at the Aberdeen Proving Grounds. The main differences compared to the preseries M2 were the different turret, some improvements of the gun mantlet and glacis armor, and an upgraded Wright radial R-975 C1 supercharged engine. The M2A1 formed thousands of tankers during the early stages of World War II.

Specifications

Dimensions M2 5.36 m x 2.6 m x 2.88 m
17ft 6in x 8ft 6in x 9ft 4 ½in
Dimensions M2A1 5.36 m x 2.6 m x 2.83 m
17ft 6in x 8ft 6in x 9ft 3in”
Total weight, battle ready M2 19.01 tons (17.24 tonnes)
Total weight, battle ready M2A1 23.52 tons (21.33 tonnes)
Crew 6 (commander, driver, 4 gunners)
Propulsion Wright Radial R975 9 Cylinder petrol/gasoline 400 hp (350 hp M2)
Max. Road Speed 30 mph (48 km/h)
Max. Road Range 130 miles (209 km)
Armament 37 mm (1.46 in) M5 tank gun
6 to 8x cal.30 (7.62 mm) Browning M1919A4 machine-guns
Armor M2 0.37 inches (9.5 mm) to 1 inch (25 mm)
Armor M2A1 0.37 inches (9.5mm) to 1.25 inches (32 mm)
Total built 2 T5, 18 M2, 94 M2A1

Sources

US Patent US2016292A “Turret Mounting” Filed 23rd July 1934, granted 8th October 1935
US Patent US2066326A “Turret Gun Mount” Filed June 28th 1934. Patented January 5th 1937
Development of Armored Vehicles Volume 1 Tanks. AGF Board no 2. September 1st 1947
Wesley Stout, “Tanks are Mighty Fine Things”. 1946 Chrysler Corporation
Peter Chamberlain and Chris Ellis, British And American Tanks of World War II, Arms and Armour Press
R.P. Hunnicutt, Sherman: A History of the American Medium Tank, Presidio Press
Steven J Zaloga, M3 Lee/Grant Medium Tank 1941-45, Osprey Publishing
TM 9-1904 Ammunition Inspection Guide March 2nd 1944

Categories
WW2 American Prototypes

T21 Light Tank

U.S.A. (1942-1943)
Light Tank Design – None built

Introduction

When the US joined the war in 1941, their primary light tank was the M3 Stuart and, while this vehicle was acceptable for that time, there was an interest in a new light tank. In January 1941, the US Army started the T7 Light Tank program, however, by August 6th, 1942, this tank had grown in weight and size and was now reclassified as the M7 Medium Tank. With no replacement for the Light Tank M3 in progress, the T21 Light Tank project was started.

While no T21 mockup would ever be made, this mockup of the T20 shows roughly what the T21 would have looked like. (Photo: Stuart)

Development

With the need for a new light tank, representatives of the Ordnance Department and the Armored Force held a conference at Fort Knox on August 18th, 1942. where it was decided that they should use the new T20 medium tank as a basis for the light tank. It would mount the M3 75 mm gun and feature armor capable of holding up against .50 caliber rounds while being within a 20-ton limit. It was decided that, if possible, the M3 75 mm gun would be replaced with a 76 mm higher velocity gun. It was proposed that it could use the Medium Tank M7’s suspension.

Following this conference and additional studies, an Ordinance Committee Minutes (OCM) was issued in February 1943 detailing the new light tank. It would have a crew of 5, mount a stabilized 76 mm gun, and would have a top speed of 45 mph (72 km/h). However, at this stage, the engine, suspension, and various other aspects were not finalized and its weight had been increased to 47,000 lbs (21,300 kg) or 21 long tons. Final layout drawings were finished during March and submitted. By this time the weight had been increased to 51,000 lbs (23,100 kg) or 22.8 long tons, with the new top speed being intended as 50 mph (80 km/h).

There was also a second variant which existed for a short time called the T21E1. This variant was to weigh 22 tons, later increased to 23 tons, and would have thicker armor than the normal T21 while being able to manage 50 mph (80 km/h). It seems likely that the T21E1 program was accepted as the new T21, as later sheets state the T21 as having almost the same figures as the T21E1.

T20 Pilot 1
T20 Pilot 1; the T21 with VVSS would have been almost identical to this. (Photo: Pershing)

Armor

The initial armor for this tank was designed to only resist .50 caliber fire, being 1 1/8th inch (2.85 cm) on the hull’s front and 1.5 inches (3.81 cm) on the turret face. The hull’s side and rear armor was 1 inch (2.5 cm) and 3/4th (1.9 cm) of an inch, respectively, the turret’s side and rear armor were 1 1/8th inch (2.85 cm). At a later point, the armor on the T21 increased to be the same armor basis as on the M5 Stuart. The T21E1 project was to have the same armor as the M5 Stuart as well.

Firepower

The T21 was to mount the 76 mm M1E1 or M1E2 gun – the primary difference between these 2 guns being that one had a tighter rifling twist rate than the other. The rounds used by that gun included M62 Armor Piercing Capped (APC) and M79 Armor Piercing (AP), additional rounds including High Explosive and White Phosphorus. The gun was to have elevation and depression limits of +25 and -10 degrees respectively, as well as being gyro-stabilized. It also was to mount two .30 caliber machine guns, one co-axially to the main gun and another in a bow mount in the hull.

Suspension and Tracks

While it was initially proposed in August 1942 to use the M7 Medium Tanks Vertical Volute Spring Suspension or VVSS, it was later decided to utilize torsion bar suspension instead. The tracks that were intended for it were the 18 inch T49 type. Whilst the exact layout is unknown, the T21 would have had, it can be assumed that due to it being just a lighter T20, it would have been the same or very similar as on the T20E3. The T20E3’s suspension had a torsion bar and initially had 3 track return rollers per side, however later on, 2 additional ones were added, bringing the total to 5 per side. an idler wheel was attached to the front wheel to compensate for slack in the track.

T20E3 Pilot
T20E3 Pilot, externally, the T21’s suspension would have been almost identical. Note the 3 return rollers (Photo: Pershing)

Engine and Transmission

The engine for both the T21 and T21E1 was to be the Ford GAN, which produced 500 bhp at 2600 RPM. The transmission for both was the same 5-speed manual transmission utilized in the M4A3. The location for the engine and transmission is unknown, but again, due to it being just a lighter T20, it is likely that it would have been in the same position as on the T20, in the rear of the tank.

Fate

In March 1943, the design and layout were presented at Fort Knox to the Armored Force. They came to the realization, from their experience with the M7 Medium Tank, that the T21’s weight would continue to increase in the future, resulting in another under-armored medium tank. They then suggested that the T21 project be terminated and Ordinance replied in July 1943 by killing the project. Up to this point, no mockup or pilot vehicles had even been started. The fate of the T21E1 is unknown, but it was almost certainly canceled along with the T21 if it was still in development at that time.

T20E3 showing the later change to 5 return rollers
T20E3 showing the later change to 5 return rollers. (Photo: Pershing)

Conclusion

This design, like many before it, was a good idea on paper, but operational realities and desires soon lead to a situation where, like the M7 before, it was doomed to become too heavy to fulfill the light tank role and too light to fulfill the medium tank role. The discontinuation of the T21 program in March 1943 was met with the start of a new project, the T24, which would not be deployed until 1944, which in turn forced the US to continue having to field the M3 and M5 Stuarts up until the end of the war, despite their growing inferiority.

The T21 Light Tank was very similar to the T20 Medium Tank from which it was derived. Illustration by Andrei “Octo10” Kirushkin, funded by our Patreon campaign.

T21 Light Tank Specifications

Dimensions (L-W-H) 5.76 m x 2.98 m x 2.48 m
Total weight, battle ready 20.98 tons (47,000lbs gross)(21.31 tonnes)
Crew Five (Driver, Co-Driver, Commander, Gunner, Loader)
Propulsion Ford GAN
Maximum speed 45mph (72kph) on road
25mph(40kph) on 3% grade
12mph(19kph) on 10% grade
Suspensions Torsion bar
Range 1150 miles at 25mph (40kph) on roads
Main Armament Gyro Stabilized 76mm M1E1 or M1E2 gun with 70 rounds
Secondary Armament Two .30 Browning M1919 machine guns with 6000 rounds
Armor 1 inch (25mm) to 1.5 inches (38mm)
Production None

Sources

Pershing: A History of the Medium Tank T20 Series, R.P Hunnicutt.
Stuart: A History of the American Light Tank, R.P Hunnicutt.
R.A.C British Army Staff (AFV) Situation Report No. 5,7,9

Categories
WW2 US Other Vehicles

Heavy Tank M6A2E1

USA (1944-45) Heavy Tank- 2 Built

Following the Allied invasion of Northern Europe in 1944, the US Department of Ordnance, believing that they would encounter heavily fortified areas such as the Siegfried Line further in northwestern Europe, decided there would be a need for a limited number of tanks with heavier armor and more powerful guns in order to act as breakthrough tanks. In order to get past these fortified areas, the M6A2E1 project was started, which would mount the turret of Heavy Tank T29 on an up-armored Heavy Tank M6A2 hull.

M6A2E1 initial draft design from July 1944; its similarity to the T26 turret is apparent here. Photo: History of the Heavy Tank, M6A2E1.

Development

The Heavy Tank T29 had started its development during August of 1944 in response to the belief that the US would need heavily armored and armed vehicles to take on fortifications and enemy vehicles that would be encountered in the advance into Europe. However, the Heavy Tank M6 was chosen for this role instead as the T29 was still in early development and would likely not be adopted and available before the Allies encountered these heavier fortifications. Ordnance, having M6 tanks left over, decided that these could be modified to meet the needs. As such, it was proposed to modify the M6 to mount the T29 turret, and to increase its armor. To do so, the M6’s turret ring would be expanded.

The M6 was a US heavy tank designed in 1940 mounting a 76 mm and a 37 mm cannon. It was in trials by 1943 but never put into service. There were 3 sub-variants of the tank made. These being the M6, M6A1 and T1E1. The M6 and M6A1 were similar, only differing in the M6 being cast and the M6A1 welded. The T1E1 was similar to the M6 but had an electrical transmission instead of a torque converter type. It had been proposed to standardize the T1E1 as the M6A2 but this was not accepted. Despite this, the M6A2 name appeared in a number of drawings and correspondence concerning the vehicle.

To increase the armor of the tank, it was decided to remove the driver’s vision door along with the hull machine gun and then weld on additional armor to achieve an effective thickness of 7 ½ inches (190.5 mm). After this was incorporated into the tank, a tentative Ordnance Committee Minute (OCM) was written up on August 14th, 1944 for a total of 15 T1E1 tanks to be modified with the 5 remaining T1E1s being used for spare parts. This new vehicle was christened the M6A2E1 in the OCM, and delivery was projected for November 15th, 1944. The Army Ground Forces, who were encouraged by the idea of the tank and the project from the start, sent a cablegram to General Eisenhower on the matter on August 2nd, 1944. General Eisenhower’s reply on the 18th was that the M6A2E1 tanks were not wanted as they were deemed impractical for use. This effectively killed the project. This may not have been a bad thing, as tests with a T1E1 (M6A2) loaded to the expected weight of 77 tons (69.8 tonnes) showed poor climbing abilities, being unable to advance on a slope of more than 40 percent (22 degrees) inclination. Given there would not have been enough time to change the drive-gear reduction, the M6A2E1 would have been limited in what terrain it could operate on.

Following this cancellation, it was requested that two should still be finished in order to test the T29’s turret and armament. This request was granted and 3 turrets were built by the Continental Foundry & Machine Company. Two of these turrets were then mounted on modified M6A2’s and were tested at the Aberdeen Proving Ground, Maryland, with the third turret being sent for ballistic testing at Watertown Arsenal, Massachusetts. The plan for additional armor of the initial designs was never implemented.


M6A2E1-1 at Aberdeen Proving Grounds on June 7th, 1945 showing the later added muzzle brake. Photo: Hunnicutt’s Firepower

Design

Turret

Despite the M6A2E1 being used as a test bed for the T29 turret, the turret design for the T29 had not been finalized and was constantly being changed, subjecting the M6A2E1 to turret modifications. The earliest of these modifications was a turret proposal dated around August 1944 calling for frontal turret armor up to 7.5 inches thick (190 mm) and a gun mounting with -10 degrees gun depression and +20 degrees elevation. In September that year, a decision was made to make three turrets for testing. Two of these were intended to be fitted onto tanks, and the third was for ballistic testing. The first mockup of this turret was seen around October. At this stage, the turret was essentially an enlarged Medium Tank T26 turret. In this initial design, much of the specifics were not fully detailed, such as where the commander would sit and if it would have one or two loaders. The front turret armor was also increased to 8 inches (203 mm) on a large external mantlet.
In December 1944, this design was further modified. The mount needed to be able to, at a minimum, provide -5 degrees of gun depression and +15 degrees elevation, and if possible -10/+20. The turret was to be traversed manually or through an electric turret drive, and no attempt was to be made at stabilizing the gun owing to limitations with the gun mount. In January 1945, a further rework was done, this time to facilitate the installation of a 155 mm gun. By February that year, a contract was placed for the production of these 2 turrets, in addition, the turret was redesigned further to be lighter and more practical. The gun was moved inwards slightly and switched to separate two-piece ammunition. In March, it was decided to increase the armor basis for the turret and gun shield.
The ammunition stowage, which was up to this point based mostly on the T26E1’s, was refined. The revised stowage now had capacity for 46 projectiles to be stored in the turret and a further 17 rounds stored in the hull, with 9 cartridge cases being carried in the turret for use as ready rack ammunition for a total of 72 rounds. In April 1945, a minor modification was done, assigning the commander a spot in the turret bulge on the center line. Due to the continual changes on the M6A2E1 and the parallel T29 project, in August, it was decided that these turrets were no longer deemed comparable to the current design for the T29’s turret and as such the M6A2E1s role of testing turret design was complete.
During these constant modifications, a side project was also started, which was primarily aimed at lightening the turret by reducing the armor thickness, although this was not applied to any the produced turrets. The intended armor for this was as of December 1944, 2.5 inches (63.5 mm) on the turret sides, 1.5 inches (38 mm) turret top, and a 3.5 inch (89 mm) gun shield.
The two produced tanks which were finished were not the same and were sub-designated M6A2E1-1 and M6A2E1-2. The M6A2E1-1 was similar to a typical M6, while the M6A2E1-2 was different, with its front plate being more vertically angled.

The M6A2E1-2 at Aberdeen Proving Grounds on October 3rd, 1945. This image shows the original gun configuration without a muzzle break. Photo: Aberdeen Proving Ground.

Armament and Fire Control

In addition to the constant turret development, the M6A2E1 was also a test bed for the T5 105 mm gun and its mounting equipment. The initial gun was based on the T4 105 mm AA gun, but had reduced barrel length and fired one piece ammunition. However, this ammunition was long and the gun would have needed to been depressed to allow loading.

The initial T5 gun, the barrel on this gun was also smaller at L48. Photo: Watervliet Arsenal
As a result, this was changed to the T5E1 gun firing two-piece ammunition. Additionally, it was decided to lengthen the barrel to the same length as the T4 105 mm AA gun. During trials, the tank fired T32E1 Armor Piercing Capped Ballistic Capped (APCBC), T29E3 High Velocity Armor Piercing (HVAP), T30E1 High Explosive (HE) and T46 White Phosphorus (WP). While these are the only known shells tested with the gun, it could have fired any round for the T5E1 105mm, such as T13 (APCBC), T37 Armor Piercing Ballistic Capped (APBC), and T182 (APBC). The tank also included a .30 caliber coaxial Browning machine gun for the gunner in the turret and on top there was a flexible AA mounting for a .50 caliber M2. For fire control, the M6A2E1 used the M70E2 sighting telescope. For indirect fire, either the M10 panoramic telescope or M62 elbow telescope would be used, and for vision, an M10 periscope was to be provided.
The commander and driver were the only people with any good vision of the outside, the gunner also had vision of the outside but this was limited to the tank’s gun optics.

Later T5E1 showing its longer L65 barrel. Photo: Watervliet Arsenal


M6A2E1 by Giganaut

Hull

The hulls of the M6A2E1’s were very similar to that of the normal M6 tank, however, a few modifications were made. The T29 turret was designed for an 80 inch (203cm) turret ring, whilst the M6 had been designed for a 69 inch (175cm) ring, so the turret ring had to be expanded.

Top-down view of the M6A2E1-1, looking at the hull and turret roof. Photo: tankarchives

Crew

This tank’s crew consisted of 5 men – 2 loaders, a gunner, a commander in the turret, and the driver in the hull.

Running Gear

The running gear consisted of Horizontal Volute Spring Suspension (HVSS) and utilized the T31 tracks, just like that on the standard M6 heavy tank.

Side profile shot of the M6A2E1-1 showing the running gear. Photo: tankarchives

Testing

The two M6A2E1’s assembled were sent to Aberdeen Proving Ground for testing. This testing was to compose of turret design and armament testing. An early fault found with the gun mounting was the use of bronze trunnion bushings. These were not strong enough and caused excessive trunnion friction with the gun and were quickly switched to needle bearings which reduced this friction to an acceptable amount. In a later firing test, during which some 119 rounds were fired, it was found that the hand wheel effort needed on the elevation mechanism gradually increased and eventually it required so much effort the firing was stopped and the unit taken apart to find the fault. Upon disassembly, it was revealed that the trunnion caps, due to a design fault, had been rubbing against a part of the firing mechanism causing increased friction during firing. While testing the gun mount and elevation systems, priority was given to strain readings on the elevation mechanism when the tank was driven cross-country. To this extent, the elevation mechanism was tested over 9 runs at 5 (8 km/h) to 10 mph (16 km/h) with the tank mounting a muzzle brake and counterweight. During this, the elevation mechanism failed during the second run at 10 mph (16 km/h) with the tension reading 105,000 lbs (47.6 tonnes).

M6A2E1-1 operating at the Churchville test course at Aberdeen Proving Grounds in July 1945 Photo: Hunnicutt’s Firepower

Fate

The tanks finished testing in 1946. Following this, the first M6A2E1-1 was displayed at Aberdeen Proving Grounds, however, in the 1950s, this tank, along with various other vehicles at Aberdeen, was sent for scrapping. The history of the second M6A2E1 produced is unknown, but if it was not scrapped at the conclusion of its testing, it was likely scrapped along with the first one later on.

M6A2E1-1 frontal view. Photo: Hunnicutt’s Firepower

Conclusion

While its design was rejected for use in combat, it was still important to the development of the T29 tank. Due to the use of existing unused T1E1s for a hull, they were able to have a tank ready that could test design choices for the upcoming T29 tank. When the tank was finished with turret design, it would find usage testing out the T5 105mm gun as well as gun mounting aspects with lessons learned from this being implemented in the T29 program.

Specifications

Dimensions (L-w-H) 11.18 x 3.12 x 3.48 m (36’8’’ x 10’3’’ x 11’5’’ ft)
Total weight, battle ready 69.85 tons (70.8 tonnes)
Crew 5 (Driver, commander, gunner, 2 loaders)
Propulsion Wright G-200 9 cylinder 960 [email protected] rpm
Maximum speed 18 mph (29 km/h) on road
Range 100 miles (160 km) on road
Armament Main: 105 mm Gun T5E1
Sec: Browning M2HB .50 Cal (12.7mm) machine gun, .30 Cal (7.62mm) Browning M1919 machine gun
Armor 1.75 inches (44 mm) to 9 inches (228 mm)
Production 2

Sources

R.P. Hunnicutt, Firepower: A History of the American Heavy Tank, Presidio Press
R.A.C Technical Situational Reports No 26, 27, 29, 30, 31, 32, 34, 35, 36, 37, 38
Aberdeen Proving Ground Photograph
Metallurgical Examination of Sections from the Cast Armor Turret made by Continental Foundry and Machine Company and two Trunnion Pins from a Heavy Tank M6A2E1 Watertown Arsenal ADA954836
Watervliet Arsenal Photographs
History of the Heavy Tank M6A2E1
Development History of the Heavy Tanks, T29 & T30
tankarchives.blogspot.com


Illustration of the Heavy Tank M6A2E1-1, produced by Tank Encyclopedia’s own David Bocquelet.