The Mark IV was a British tank of the First World War. Introduced in 1917, it benefited from significant developments of the Mark I tank . The main improvements were in armour, the re-siting of the fuel tank and ease of transport. The Mark IV was first used in mid 1917 at the Battle of Messines Ridge. A large number of these tanks were also used for development work. In an attempt to improve trench-crossing capability, the "tadpole tail", an extension to the rear track horns, was introduced. Designer M Bergman