The first British tank, the Mark I of World War I, was introduced to break through German defensive lines of trenches and barbed wire.
When lighter, faster tanks were introduced, the larger tanks were classified as heavy.

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.

American forces rarely fielded heavy tanks, as they still held on to the infantry-support doctrine like the British; in addition, the Americans recognized the logistical and mobility issues that came with possessing a heavy tank force and did not want to compromise its 3,000 mile supply line to Europe.
As a result, the US instead preferred to use tank destroyers for anti-tank combat, and prior to 1944 there were few indications that the M4 Sherman was outclassed in terms of armor and weapons by German heavy tanks.
Near the end of World War II, the M26 Pershing was sent to Europe in limited numbers, being the closest the Americans had to a heavy tank other than the up-armored M4 Sherman Jumbos.
The first British tank, the Mark I of World War I, was introduced to break through German defensive lines of trenches and barbed wire. When lighter, faster tanks were introduced, the larger tanks were classified as heavy.
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.
American forces rarely fielded heavy tanks, as they still held on to the infantry-support doctrine like the British; in addition, the Americans recognized the logistical and mobility issues that came with possessing a heavy tank force and did not want to compromise its 3,000 mile supply line to Europe. As a result, the US instead preferred to use tank destroyers for anti-tank combat, and prior to 1944 there were few indications that the M4 Sherman was outclassed in terms of armor and weapons by German heavy tanks. Near the end of World War II, the M26 Pershing was sent to Europe in limited numbers, being the closest the Americans had to a heavy tank other than the up-armored M4 Sherman Jumbos.
Heavy tank