WORLD WAR 2 IN REVIEW: M6: American Heavy Tank

The Heavy Tank M6 was an American heavy tank designed during World War II. The tank was produced in small numbers and never saw combat.

Development History

Because of limited budgets for tank development in the interwar years, at the outbreak of World War II the United States Army possessed few tanks, though it had been keeping track of the use of tanks in Europe and Asia. Successful employment of armored units in 1939–40, mostly by the Germans, gave momentum to a number of US tank programs, including a heavy tank. The United States possessed a massive industrial infrastructure and large numbers of engineers that would allow for mass production of tanks.

Following the Chief of Infantry recommendation from May 1940, the US Army Ordnance Corps started to work on a 50-ton heavy tank design. The project was approved in June and the vehicle received the designation Heavy Tank T1.

Initially, a multi-turreted design was proposed, with two main turrets each armed with a low-velocity T6 75 mm (2.95 inch) gun, a secondary turret with a 37 mm gun and a coaxial .30 caliber (7.62 mm) machine gun, and another secondary turret with a 20 mm gun and a coaxial .30 caliber machine gun. Four .30 caliber machine guns were to be installed in ball mounts, two in the glacis (front) plate and two in the rear corners of the hull. The design was somewhat similar in concept to multi-turreted breakthrough tanks developed in Europe in the 1920s and throughout the 1930s, such as the 1925 British Vickers A1E1 Independent or the Soviet T-35 of the early 1930s, albeit on a much more powerful scale: the older tank designs were typically armed with a single light or medium-caliber main gun and multiple machine guns, and had armor only sufficient to protect from small arms fire. Later in the decade, however, European tank developers switched to single-turret designs.

By October, the US developers reached the same conclusion as their European counterparts. The armament was changed to a single vertically stabilized 3-inch (76.2 mm) gun and a coaxial 37 mm gun in a single three-man turret with both manual and electric traverse. The turret had a commander's cupola identical to that of the M3 Medium Tank.[clarification needed] Additional armament consisted of two .50 caliber machine guns in a bow mount (operated by the assistant driver), two .30 caliber machine guns in the front plate (fired electrically by the driver), one .30 caliber in the commander's cupola and one .50 caliber in a rotor mount for anti-aircraft use in the right rear of the turret roof (operated by the loader). The crew consisted of commander (seated in the turret left), gunner to the right of the gun, gun loader (turret), driver and assistant driver in the front left and right of the hull respectively, and another crewman in the hull to pass ammunition to the turret.

One of the main challenges was developing a powerpack for such a heavy vehicle. The Wright G-200 air-cooled radial gasoline engine was selected by a committee formed by the Society of Automotive Engineers, but no suitable transmission was available. The committee recommended developing a hydramatic transmission, while a possibility of using a torque converter or an electric transmission was also to be checked.

The project was first publicly disclosed in August 1940 when the Army awarded Baldwin Locomotive Works in Pennsylvania a $5.7 million contract for the production of 50 tanks. The Army envisioned building 500 of this type.

The first T1E1 was delivered to the Army in December 1941. From 1941 to 1942, three prototypes were built: one with electric transmission and two with torque converter transmission. Variants with hydramatic transmission were never completed. The prototypes also differed in hull assembly method: one had a welded hull and two had cast hulls.

On 26 May 1942, two variants with torque converter transmission were standardized as M6 (cast hull) and M6A1 (welded hull). Standardization of the electric transmission equipped T1E1 as the M6A2 was never approved, but the manufacturing of the vehicle was nevertheless recommended. It was proposed by the Ordnance Corps that 115 T1E1s would be built for the US Army for "extended service tests", between that and Services of Supply instruction to increase production with the balance going to aid US allies, this would mean 50 M6s and 65 M6A1s built for the British. Production started in December 1942.

Some minor changes were introduced in the production vehicles: the cupola was replaced by a double-door hatch with a ring mount, while the machine gun in a rotor mount and the left front machine gun were removed.

However, by the time the M6 was ready for production, the Armored Corps had lost interest in the project. The advantages the M6 offered over medium tanks – its much thicker armor and slightly more powerful gun – were offset partly by the shortcomings of the design – such as very high silhouette, awkward internal layout and reliability problems – and partly by logistical concerns due to its weight.

In early 1942, the Ordnance Department set a production target of 250 a month, with Fisher as a second contractor to meet a planned expansion in the size of the army. However, by September, the focus had changed, with tank production scaled back and more aircraft for the USAAF. Under this new "Army Supply Program", the M6 production was cut from 5,000 to a little over 100.

By the end of 1942, the Armored Corps were of the opinion that the new M4 Sherman gave adequate solution for the present and the near future, while being reliable, cheap and much easier to transport and they had no need for a heavy tank. In 1943, the production target was reduced again, down to 40, being an economic cut-off.

Production M6 and pilot M6A1 examples were evaluated at Fort Knox in the early part of 1943. The reports were critical of the awkward and inefficient crew stations, and the superfluous 37mm gun. However, in October, the tank had performed well enough at Aberdeen Proving Ground to proceed.

The Ordnance Corps had expected the 76 mm gun to be lacking, and the T1E1 prototype was tested with a T7 90 mm gun and was found to be a satisfactory gun platform, although the poor turret layout was again noted. By this point, the M6 had been cancelled.

In August 1944, the Ordnance Corps recommended modifying the T1E1s to build 15 specially armored and armed tanks to meet a need for attacking heavily fortified areas. These 77-ton vehicles – designated M6A2E1 – with thicker (equivalent to 7.5-inch (190 mm) vertical protection) glacis armor and a turret developed for the T29 Heavy Tank, armed with a T5E1 105 mm gun but no increase in engine power. Ordnance believed they could be delivered by November. The proposal was put to the supreme commander in Europe General Eisenhower, who rejected them as impracticable. Two tanks were used to test the T29 turret and gun, but their armor was not modified.

On 14 December 1944, the M6 was declared obsolete. Only 40 had been produced and they never left US soil. Several toured the United States for propaganda purposes, where they gave performance displays (such as car crushing) at War Bond drives and the like. All were eventually scrapped except for a single T1E1, which was put on display at the United States Army Ordnance Museum, Aberdeen, Maryland.

The British used the horizontal volute spring suspension system of the M6 in the first of their two A33 Heavy Assault Tank "Excelsior" prototypes.

Type: Heavy tank

Place of origin: United States

In service: trials only

Used by: United States Army

Wars: World War II

Designer: US Army Ordnance Corps

Manufacturer: Baldwin Locomotive

Number built: 40

Variants: 6

Variants

T1: Cast hull, hydramatic transmission. Never built.

T1E1: Cast hull, General Electric electrical transmission. Standardization proposed as M6A2 but not accepted. 20 units built.

T1E2 / M6: Cast hull, torque converter transmission. 8 units built.

Weight: 126,500 lb (57.4 tons) combat loaded

Length: 27 ft 8 in (8.43 m) gun forward

Width: 10 ft 3 in (3.12 m) over track armor

Height: 9 ft 10 in (3.0 m) to turret roof

Crew: 6 (commander, gunner, driver, assistant driver, loader, assistant loader)

Armor: 25–83 mm

Main armament:

1 × 3in (76.2 mm) gun M7 (75 rounds)

1 × 37 mm (1.46 in) gun M6 (202 rounds)

Secondary armament:

2 × .50 cal (12.7mm) Browning M2HB machine guns, hull (6,900 rounds)

2 × .30 Browning M1919A4 machine guns, one fixed (bow), one flexible AA (5,500 rounds)

Engine: 1,823 in³(29.88 L) Wright G-200 9-cylinder gasoline; 825 hp at 2,300 rpm

Power/weight: 15.7 hp/ton

Transmission: Timken mechanical model 16001, three speeds (two forward, one reverse); rear drive sprocket

Suspension: Horizontal volute spring

Ground clearance: 20.5 in (52 cm)

Fuel capacity: 477 US gallons (1,810 L)

Operational range: 100 miles (160 km)

Speed: 22 mph (35 km/h)

T1E3 / M6A1: Welded hull, cast turret, torque converter transmission. 12 units built.

T1E4: Welded hull, hydramatic transmission. Four GM engines. Cancelled 1942. Never built.

M6A2E1: Uparmored T1E1 fitted with a new turret with a T5E1 105 mm gun. Used for testing T29 heavy tank project armament system.

Sources

Chamberlain, Peter & Ellis, Chris (1969), British and American Tanks of World War II, Arco Publishing

Hunnicutt, Richard Pearce (1988), Firepower: A History of the American Heavy Tank, Novato, California: Presidio Press, ISBN 0-89141-304-9

Icks, Robert J. (1971), No. 32: The M6 Heavy and M26 Pershing, AFV Weapons, Profile Publishing

M6 Heavy Tank.

T1E1 Heavy Tank prototype.

Front view of Heavy Tank M6, with several early M3 Light Tanks in the background.

A U.S. Army M6 Heavy Tank in December 1941. Original caption: “Delivery of the first heavy tanks. This is the new 57-ton tank, known as the M1 in the initial demonstration. Notice that the gun turrets are on the top, making it possible for the tank to take advantage of irregular land, sheltering the lower part and shooting from revolving turrets on top. In the turret are 3-inch guns and a 37mm anti-aircraft gun.”

M6A1 Heavy Tank. Note its angular welded hull, as opposed to rounded cast hulls of M6 and T1E1.

T1E1 Heavy Tank.

The position of the M6 Heavy Tank’s weapons are illustrated in this picture. No coaxial machine gun was mounted, meaning that the tank commander had to expose himself to provide machine gun fire to the vehicle’s sides or rear.

Although externally identical to the M6, the T1E1 Heavy Tank was driven by an electric drive system instead of a more conventional transmission. This vehicle is fitted with the center guide T31 tracks. These were made from a set of the outside guide tracks where the center guide replaced the center connector, and the outside guides were removed by flame cutting. Note the partially-open driver’s visor on this tank.

M6 Heavy Tank during a public demonstration.

M6 Heavy Tank.

Upper rear view of an M6 Heavy Tank.

In early 1944 the T1E1 Heavy Tank was fitted with an experimental mounting of the 90mm Gun T7 using a turret based on that of the Heavy Tank M26 with the hull stowage rearranged for 90mm ammunition. Project was cancelled in March 1944.

General Barnes and key members of the industry view a model of the T1 Heavy Tank.

M6 Heavy Tanks, Aberdeen Proving Ground, Maryland, circa 1950s.

M6 Heavy Tank (probably same vehicle as seen in the previous photo), Aberdeen Proving Ground, Maryland, July 1974.

Initial T1 design. The first production T1E2 looked very similar to this. Interestingly, this drawing indicates the tank used VVSS suspension at this point.

Pilot T1E2 at the Baldwin Locomotive Works on September 19, 1941. At this time, the mounts for the driver’s two .30 caliber machine guns had not been installed. Note the original bow gunner’s mount.

Rear of the first T1E2, showing the rear machine gun emplacement and large muffler.

Heavy Tank M6, mounting a 3-inch gun, produced by Baldwin Locomotive Works, is inspected by (from left) Lt.Col. David N. Hauseman, Brig.Gen. Gladeon M. Barnes, William H. Harmon (Baldwin official), and Capt. Arthur J. Seiler, December 1941.

A view of the redesigned rear on the T1E2 pilot. Note the rotor machine gun turret and cupola.

Front view of the T1E2 Pilot. Note that the bow gunner’s gun sight is broken and bent. The man in the photo is Brigadier General William Ayes Borden.

Production M6. Note the lack of cupola and round sides showing the cast construction.

T1E2 Pilot crushes a truck during a demonstration.

M6 with features labeled.

Production M6, note the rounded sides of the cast hull.

M6 Heavy Tank alongside a Light Tank M5.

T1E2 Pilot alongside an M3. Note the original two .30 cal machine guns in the hull for the driver. On production vehicles, only the right machine gun was retained.

SCR-506-T2.

T1E1 pilot on a pontoon bridge, December 1941.

M6 showing the rutted ground and obstacles believed to have caused track throwing.

M6A1 front view showing the redesigned machine gun mount and drivers hatch opened. Note how clogged the grousers on the tracks are with mud.

Cutaway of the T1E1, showing the large engine.

M6, M4, M5 in line.

T1E1 Pilot delivered without armament.

M6 Heavy Tank on display. Note German Panzer VI Tiger I in background.

90 mm T7 gun.

T1E1 with 90 mm gun installed.

The M6A2E1 was a modified M6A2 with a new heavy turret and the T15E1 105mm Gun, in anticipation of demands for assault tanks from the European theater. Aberdeen Proving Ground, 7 June 1945.

A selection of M6 tanks, most likely all of them manufactured, excluding the two M6A2E1s and three Pilot vehicles, at Rock Island Arsenal May 29, 1945.

The M6 heavy tank was nothing if not imposing, as this view illustrates. The smooth lines of the cast hull are apparent here. Hidden behind the 3-inch gun is the coaxial 37mm gun, which was the main armament of the M2 medium tank produced three years previously. A .50 cal. machine gun is partially hidden by the open turret hatch, and two more .50 cal. machine guns were mounted in the right bow. Just behind the pistol port for the assistant driver is an antenna mount.

Heavy tank M6A2E1.

T1E2 pilot tank being tested, December 1941.

T1E2 (M6) at Baldwin Locomotive Works, December 1941.

Front side of the M6A2E1.

Rear side of the M6A2E1.

T1E2 at Baldwin Locomotive Works side view, December 1941.

M6A2E1 Number 2 at Aberdeen Proving Grounds.

M6 heavy tank next to an M3 Stuart light tank at Aberdeen Proving Ground, circa 1941.

Pilot T1E2 as it arrived at the Aberdeen Proving Ground.

Heavy tank M6 on the General Motors test site, 4 August 1943.

Production pilot heavy tank M6А1 at the General Motors test site, 22 January 1943. Outwardly, there are almost no differences from the M6, with the exception of the welded body.