America's Heavy Tanks and Tank Destroyers in WWII: From M6 to M36 Jackson America’s WWII armor evolution produced massive powerhouses like the M6 Heavy Tank and the M36 Jackson. Developed in the early 1940s, the M6 reached 22 mph but was deemed too cumbersome for overseas shipment. Conversely, the M36 Jackson, introduced in 1944, became a battlefield legend. Reaching speeds of 30 mph, it packed a devastating 90mm gun specifically designed to pierce heavy German armor at long ranges. These vehicl