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Heavy Tank M6
USA (1942)
Heavy tank- about 45 built
Little known, the M6 was the first modern US heavy tank. The only other heavy tank built in series was the Liberty or Mark VIII, a joint US-British design, produced in 1918, of the WWI-era lozenge type. When the Second World War broke out, the successful German campaign of 1940 gave a spur to US tank development. Already, on 20 May 1940, the Chief of Infantry recommended to the US Army Ordnance Corps to study a 50-ton tank design. The first one was a projected multi-turreted model with two main 75 mm (2.95 in) turrets, a secondary one with a 37 mm (1.46 in) gun and coaxial M1919A4, and another, smaller turret with a 20 mm (0.79 in) gun and coaxial cal.30 (7.62 mm), plus four cal.30 machine guns in each corner of the tank in ball mounts. In was approved on 11 June 1940 under the ordinance prototype registration T1 heavy tank. The T1 had to be fitted with a cast hull and hydramatic transmission. However, this design already appeared outdated. In October, this design was changed to a more conventional approach, with a single turret armed with a 76.2 mm (3 in) and a 37 mm gun (1.46 in).
http://www.tanks-encyclopedia.com/ww2/US/M6A1_Heavy_Tank.php

Here is a colour photo

And another view