The British Mark I was the world's first combat tank, entering service in August 1916, and first used in action on the morning of 15 September 1916. It was developed to be able to cross trenches, resist small-arms fire, travel over difficult terrain, carry supplies, and be able to capture fortified enemy positions. The Mark I was a development of Little Willie, the experimental tank built for the Landships Committee by Lieutenant Walter Wilson and William Tritton in the summer of 1915. A small number of Mark I tanks took part in the battle of the Somme during the Battle of Flers-Courcelette in September 1916.

No one individual was responsible for the development of the tank. Rather, a number of gradual technological developments brought the development of the tank as we know it closer until its eventual form was unveiled out of necessity by the British Army. The British Army designs were forced by the trench warfare in which neither side could achieve more than small incremental gains without heavy loss of soldiers lives, but tanks changed that. They were made to cross the trenches and quickly break into the enemy rear, while other tanks supported the main attack. The development between the infantry tank and the cruiser tanks had its origins in the First World War division between the first British heavy tanks which supported the infantry and the faster Whippet

Matilda tanks at Tobruk

Tanks first appeared on the battlefield as a solution to trench warfare. They were large, heavy, slow moving vehicles capable of driving right over the top of enemy trenches; thereby eliminating the need to send soldiers "over the top" only to be blasted to pieces by enemies. The British Army was the first to use them, who built them in secret to begin with. To keep the enemy from finding out about this new solution, the public were informed that the vehicles were large water carriers, or tanks, and the name stuck.