The Tank, Cruiser, Mk I (A9) was a British cruiser tank of the interwar period. It was the first cruiser tank: a fast tank designed to bypass the main enemy lines and engage the enemy’s lines of communication, along with enemy tanks.
Designed by Sir John Carden of Vickers-Armstrongs the prototype of this tank appeared in 1936. It was designed originally as a Medium Tank with the official designation A9 but was described as a Cruiser Tank when it entered production in 1937. In addition to light tanks for reconnaissance the idea was to build infantry tanks for infantry support and cruisers to fulfil the cavalry role. A cruiser tank was therefore intended to be fast and lightly armoured.