The Mark IV was a British tank of the World War I. Introduced in 1917, it benefited from significant developments on the first British tank, the intervening designs being small batches used for training. The major improvements were in armour, the re-siting of the fuel tank, and easier transportation. A total of 1,220 were built: 420 "Males", 595 "Females" and 205 Tank Tenders (unarmed vehicles used to carry supplies), which made it the most produced British tank of the War.The Mark IV was first used in mid 1917 at the Battle of Messines Ridge. It remained in official British service until the end of the War, and a small number served briefly with other combatants afterwards.