United States' M6 heavy tank

Photos

Design

After the invasion of the Low Countries and France in 1940 the Chief of Infantry requested two types of heavy tanks to be developed.⁶ One would be similar to the M2 Medium with 3" of armor, a hull mounted 75 mm gun, and a turret with a 37 mm or 50 mm gun.⁶ This eventually led to the M3 Medium.^1,6 The second, which became the M6 Heavy, was not to be over 80 tons, have 3" of armor, a hull gun from 75 mm to 105 mm, and a 37 mm or 50 mm in the turret.⁶ Spread throughout the vehicle were to be eight machine guns.⁶

In 1940 this was changed to have the main gun be a 76 mm and have the 37 mm coaxially mounted.¹

The final drive was mounted behind the engine. The transmission was connected by a flexible coupling without the use of a propeller shaft. There was a pedal that occupied the position normally occupied by the clutch petal, and this served as a transmission brake pedal.

The 3" gun was mounted with the 37 mm gun. A gyrostabilizer was provided as well.

There were 4 bogie assemblies on each side. Each had 4 bogie wheels. Two riding on the outside half of the track and 2 on the inside. Two springs were mounted on each assembly. The driving sprocket was at the rear. There was a main idler in the front and there was a nonadjustable idler between the main idler and the front bogie assembly.

Six periscopes were provided. There were 4 escape doors.

Design Changes

After over 3,500 miles of testing, in April 1942, it was decided to completely redesign the brakes and cooling system due to flaws that were found.⁶ The new brakes were similar to train engine brakes as they were hydraulically operated disc brakes applied to the differential.⁶

Production Withdrawn

The Armored Board decided that the M6 was too heavy and unreliable so they recommended that the contracts should be cancelled.^5,6 The Ordnance Department said it could modify the design of the M6 to rectify these problems but the Army Ground Forces decided it didn't want the M6.^5,6 In September 1942 orders were reduced to 115, with 50 of those going to the British Army.^5,6 Also, the Armored Forces felt that the M6 would take up too much shipping space as two M4 Mediums could fit in the same space a single M6 would fit.⁶

Prototypes

Originally four prototypes were to be built, each with a different power train, but two of these required changes to the hull so only two were authorized.^1,6
Four prototypes were constructed in February 1941.¹ They were designated the T1E1 - T1E4. The cast hulled version with a torque converter was choosen.¹

The engine for the prototypes was the Wright G-200 9 cylinder air cooled aircraft engine that produced 825 HP.⁶

T1, Hydraulic Transmission

The T1 was to have the torque converter transmission (see below) but delays in producing the complex torque converter caused it to have a hydraulic transmission.⁶

The T1 was had a turret and was armed with a 3" T9 antiaircraft gun.⁶ Coaxially it had a M5E1 37 mm gun.⁶ Two .50 cal machine guns were mounted in the hull for the assistant driver to operate.⁶ Initially the driver had two .30 cal machine guns as well.⁶ The commander had a .30 cal machine gun in his cupola.⁶

T1E1, Gasoline Electric Transmission

The tank engine provided power to two motors that drove each track.⁶ Braking and steering changed the amount of current going to these engines which controlled the speed of the tracks.⁶ As this transmission was flexible, one track could go forward while the other went reverse allowing the tank to rotate on its own axis.⁶

The T1E1 didn't have a formal turret installed and was never armed as it was only used to test the transmission.⁶ It could go 25 mph but only had a range of 100 miles.⁶

British observers followed the tests as the TOG had a similar transmission.⁶

T1E2, Torque Converter

A form of hydraulic transmission, the torque converter, applied the power to the final drive via a variable torque speed ratio.⁶ The ratio was automatically selected based upon the load placed on the engine.⁶

Innovative Design

For 1940, the design was innovative as it had the turret and hull made from castings.⁶ There were no side doors as the hatches were in the top and escape hatches in the bottom.⁶ There was a track skirt installed on each side to protect the suspension which was unique for an United States design.⁶

Production

In April 1942 the T1E2 was standardized as the M6 Heavy Tank.⁵

By September 1942, orders for 5,000 M6s were placed.^5,6

On December 7, 1942, the Chief of the Armored Forces recommended that all production be stopped immediately as the M6 series was no longer needed.⁶

• T1: 1⁶
• T1E1: 1⁶
• T1E2: 1⁶
  • Production: December 1941⁶
• T1E3: 1⁶
• M6: 7⁶
  • Manufacturer: Baldwin Locomotive⁶
  • Production: December 1942 - ?⁶
• M6A1: 11⁶
• M6A2: 18⁶
  • Manufacturer: Baldwin Locomotive Co.⁴
• Total: 40^6,7
  • Manufacturer: Fisher Body Division (12)⁶, Baldwin Locomotive (28)⁶

Variants

• T1: Prototype.⁶ Hydraulic transmission.⁶
• T1E1: Prototype.⁶ Gasoline electric transmission.⁶ Became the M6A2.⁶
• T1E2: Prototype.⁶ Torque converter transmission.⁶ Was selected to become the M6.⁶
• T1E3: Prototype.⁶ Became the M6A1.⁶
• T1E4: Prototype, never constructed.⁶ Was to have welded hull and a cast turret.⁶ Four diesel engines were to be installed. with two torquematic transmissions.⁶
• M6: Had cast hull¹ and turret. It had a torque converter transmisison.¹
• M6A1: Had a cast turret and welded hull¹. It had a torque converter transmission.¹
• M6A2: Cast hull with electric transmission.¹
  The 3" gun could fire a 15 lb shell at a muzzle velocity of 2,600'/sec.⁴ The 37 mm could fire a 1.91 lb shell at 2,600'/sec.⁴
• M6A2E1: Had 105 mm T15E1 gun installed expecting the better armament would be needed in Europe.⁶ Fifteen were to be converted, but in July 1944 it was cancelled.⁶

Usage

Never saw service.¹