British heavy tanks of the First World War

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. 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 a 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.

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 Willie. A gun turret above the hull would have made the centre of gravity too high when climbing a German trench parapet (which were typically 4 ft, 1.2 m high), so the tracks were arranged in a rhomboidal form around the hull and the guns were put in sponsons on the sides of the tank. The reworked design was also able to meet the Army requirement to be able to cross an 8 ft (2.4 m) wide trench.

A mockup of Wilson's idea was shown to the Landship Committee when they viewed the demonstration of Little Willie. At about this time, the Army's General Staff was persuaded to become involved and supplied representatives to the committee. Through these contacts Army requirements for armour and armament made their way into the design. The prototype Mark I, ready in December 1915, was called "Mother" (also known at various times as "The Wilson Machine", "Big Willie", and officially "His Majesty's Land Ship Centipede"). Mother was successfully demonstrated to the Landship Committee in early 1916; it was run around a course simulating the front including trenches, parapets, craters and barbed wire obstacles. The demonstration was repeated on 2 February before the cabinet ministers and senior members of the Army. Kitchener, the Secretary of State for War, was skeptical but the rest were impressed. Lloyd George, at the time Minister of Munitions, arranged for his Ministry to be responsible for tank production.

The Landship Committee was re-constituted as the "Tank Supply Committee" under the chairmanship of Albert Stern; Ernest Swinton, who had promoted the idea of the tank from the Army angle was also a member. General Haig sent a staff officer Hugh Elles to act as his liaison to the Supply Committee. Swinton would become the head of the new arm, and Elles the commander of the tanks in France.

The first order for tanks was placed on 12 February 1916, and a second on 21 April. Fosters built 37 (all "male"), and Metropolitan Carriage, Wagon, and Finance Company, of Birmingham, 113 (38 "male" and 75 "female"), a total of 150.

When the news of the first use of the tanks emerged, Lloyd George commented,