The M4/M4A3 Sherman tank was produced in several variants and it was also the basis for a number of related vehicles. In addition Shermans have been modified by several nations from modernization upgrades to complete hull conversions for another task.
When the Sherman Tank was initially created it was designed around US theory about how medium tanks, and full-track armored vehicles in general, should be utilized on the battlefield. In US doctrine the medium tank's job was to assist infantry in the assault and provide a base of fire to fight from. Taking on enemy tanks were the job of purpose-built tank destroyers. The UK, which was a major user of the Sherman, differed in doctrine - tanks were expected to engage enemy tanks.
The wide array of special duties that a tank could be used for were just being explored by armies around the world in the early 1940s. Theories of what vehicles were supposed to be engaging enemy tanks changed as vehicles like the Shermans often found themselves up against enemy armor, some of the most important initial changes centered around upgunning the basic vehicle. Improving the vehicles mobility, protection, and creating specific variants for infantry support roles soon followed. Similar modification of the main armament would be done by the British who received a number of Shermans during the course of the war. Turning earlier variants of the Sherman into Armored Personnel Carriers or "Kangaroos" was also common, as was turning them into recovery vehicles.
More radical variants followed, first with experiments with flotation screens in preparation for the invasion of Europe by Allied forces in 1944, and later by the addition of rocket launching equipment mounted on the turret. Extensive work on creating mine clearance devices to be attached to Shermans or out of Shermans in some fashion was also conducted up until the end of the Second World War.
After the end of the Second World War large numbers of surplus Shermans were supplied to other nations, but primarily to South America and the Middle East. Israel became the largest post-war user of Sherman tanks, conducting extensive modifications to keep them in front line service right up into the early 1970s as tanks, mobile artillery pieces, armored ambulances and more. Many saw action in the 1973 October War. Similar modifications and purchases of Israeli-modified Shermans was done in South America where they served on as the last fighting Shermans right up until 1989.