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. A total of 1,220 Mk IV were built: 420 "Males", 595 "Females" and 205 Tank Tenders, which made it the most numerous British tank of the war. The Mark IV was first used in mid 1917 at the Battle of Messines Ridge. It remained in British service until the end of the war, and a small number served briefly with other combatants afterwards.