British heavy tanks were a series of related armoured fighting vehicles developed by the UK during the First World War. The Mark I was the world's first tank, a tracked, armed, and armoured vehicle, to enter combat. The name "tank" was initially a code name to maintain secrecy and disguise its true purpose by making it appear to be a water transport vehicle for bringing water to the troops at the front line. The tank was developed in 1915 to break the stalemate of trench warfare. It could survive the machine gun and small-arms fire in "no man's land", travel over difficult terrain, crush barbed wire, and cross trenches to assault fortified enemy positions with powerful armament. Tanks also carried supplies and troops. British heavy tanks are distinguished by an unusual rhomboidal shape with a high climbing face of the track, designed to cross the wide and deep trenches prevalent on the battlefields of the Western Front. Due to the height necessary for this shape, an armed turret would have made the vehicle too tall and unstable. Instead, the main armament was arranged in sponsons at the side of the vehicle. The prototype, named "Mother", mounted a 6-pounder (57 mm) cannon and a Hotchkiss machine gun at each side. Later, subtypes were produced with machine guns only, which were designated "Female", while the original version with the protruding 6-pounder was called "Male". 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. Development The Mark I was a development of Little Willie, the experimental tank built for the Landship Committee by Lieutenant Walter Wilson of the Royal Naval Air Service and William Tritton of William Foster Co., between July and September 1915. It was designed by Wilson in response to problems with tracks and trench-crossing ability discovered during the development of Little