World War I
Modern armoured warfare began during the First World War with the need to break the tactical, operational and strategic stalemates forced on commanders on the Western Front by the effectiveness of entrenched defensive infantry armed with machine guns—known as trench warfare. Under these conditions, any sort of advance was usually very slow and caused massive casualties. The development of the tank was motivated by the need to return manoeuvre to warfare, and the only practical way to do so was to provide caterpillar traction to (machine)guns allowing them to overcome trenches while at the same time offering them armour protection against small arms (rifle, machine gun) fire as they were moving.
British heavy tank of World War I
Tanks were first developed in Britain and France in 1915, as a way of navigating the barbed wire and other obstacles of no-man's land while remaining protected from machine-gun fire. British Mark I tanks first went to action at the Somme, on 15 September 1916, but did not manage to break the deadlock of trench warfare. The first French employment of tanks, on 16 April 1917, using the Schneider CA, was also a failure. In the Battle of Cambrai (1917) British tanks were more successful, and broke a German trenchline system, the Hindenburg Line.
Despite the generally unpromising beginnings, the military and political leadership in both Britain and France during 1917 backed large investments into armoured vehicle production. This led to a sharp increase in the number of available tanks for 1918. The German Empire to the contrary, produced only a few tanks, late in the war. Twenty German A7V tanks were produced during the entire conflict, compared to over 4,400 French and over 2,500 British tanks of various kinds. Nonetheless, World War I saw the first tank-versus-tank battle, during the Second Battle of Villers-Bretonneux in April 1918, when a group of three German A7V tanks engaged a group of three British Mark IV tanks they accidentally met.
After the final German Spring Offensives of 1918, Entente tanks were used in mass at the Battle of Soissons and Battle of Amiens, which ended the stalemate imposed by trench warfare on the Western Front, and thus effectively ended the war.
Tactically, the deployment of armour during the war was typified by a strong emphasis on direct infantry support. The tank's main tasks were seen as crushing barbed wire and destroying machine-gun nests, facilitating the advance of foot soldiers. Theoretical debate largely focused on the question whether a "swarm" of light tanks should be used for this or a limited number of potent heavy vehicles. Though in the Battle of Cambrai a large concentration of British heavy tanks effected a breakthrough, it was not exploited by armour. The manoeuvrability of the tank should at least in theory regain armies the ability to flank enemy lines. In practice, tank warfare during most of World War I was hampered by the technical immaturity of the new weapon system causing mechanical failure, limited numbers, general underutilisation, a low speed and a short range.
Strategic use of tanks was slow to develop during and immediately after World War I, partly due to these technical limitations but also due to the prestige role traditionally accorded to horse-mounted cavalry. An exception, on paper, was the Plan 1919 of Colonel John Fuller, who envisaged using the expected vast increase in armour production during 1919 to execute deep strategic penetrations by mechanised forces consisting of tanks and infantry carried by lorries, supported by aeroplanes, to paralyse the enemy command structure.
Following the First World War, the technical and doctrinal aspects of armoured warfare became more sophisticated and diverged into multiple schools of doctrinal thought.