The Mark I entered service in August 1916, and was first used in action on the morning of 15 September 1916 during the Battle of Flers-Courcelette, part of the Somme Offensive. With the exception of the few interim Mark II and Mark III tanks, it was followed by the largely similar Mark IV, which first saw combat in June 1917. The Mark IV was used en masse, about 460 tanks, at the Battle of Cambrai in November 1917. The Mark V, with a much improved transmission, entered service in mid-1918. More than two thousand British heavy tanks were produced. Manufacture was discontinued at the end of the war.