The Cruiser Tank, Mark I (A9) was the first the British cruiser tanks, a pre-war concept that involved fast moving armor that could exploit breakthroughs created by the infantry in much the same way as cavalry did in the past. The concept was flawed from the start and resulted in British tanks being chronically under-gunned and poorly protected compared to the German tanks they faced throughout the war. The Cruiser Mk I was designed by Sir John Carden as early as 1934 but was constrained by financial limitations that forced the adoption of a commercial powerplant as well as vastly reduced armor protection compared to the medium tanks it was designed to replace (the hull was also riddled with shot traps). Armament was composed of the 2-pounder gun, too weak against even early-war German armor, and the small size resulted in cramped conditions for the turret crew and driver who shared the compartment. The suspension featured a triple-wheel bogey system with outer wheel being noticeably larger than the inner pair, and offered relatively decent cross-country performance although its maximum speed was not particularly impressive for a cruiser tank. Mark Is were used by the 1st Armoured Division in France in 1940 but most were lost during the campaign or after Dunkirk. After this, a few were deployed to North Africa but it was retired in 1941 by which time its obsolescence was obvious.

The A9 design began life as a medium tank but was later re-conceived as the Cruiser Tank, Mark I. An initial contract was offered in 1937 with deliveries beginning the following year and production undertaken by both Vickers as well as Harland and Wolff of Belfast. The basic tank variant was known as the Cruiser Mk. I with the only modification being the Cruiser Mk. I CS close support vehicle armed with a 3.7-in short-barreled howitzer.