Heavy tank
The Char 2C was one of the largest tanks ever produced. At the start of World War II, France and the Soviet Union were the only countries to have inventories of heavy tanks, such as the Char B1, T-35, and KV-1. The Matilda II was designed under the British infantry tank concept which is similar to the heavy tank having thick armor and weighing more than their other tanks. It’s usually separate because they have less firepower with their cruiser tanks (comparable to mediums) at the time having the same main armament but more machine guns. Later war examples were the German Tiger I and II, as well as the Soviet IS series. Note that "heavy" versus "medium" is more a question of tactical roles than weight; the Panther, for example, was a "medium" tank that outweighed most Allied "heavy" tanks.
History of the oil tanker
The increase in scale brought a new problem. Until then, the washing of tanks after cargo discharge was done by water. In December 1969 three tankers exploded during tank washing. The Dutch Shell tanker "Marpessa" sank off Dakar and became the largest merchant vessel ever lost. The other two, the British Shell tanker "Mactra" and the Norwegian "Kong Haakon VII" were damaged heavily, but remained afloat. Shell investigated the matter and came to the conclusion that water drops that impact steel with high velocity generates static electricity that can cause explosions in combination with cargo vapors. This only became apparent with the large sizes of the tanks of VLCC's.