The origin of the Cruiser concept
During the interwar the doctrine of the War Office changed, especially after testing different tankettes, the Medium Mk.I and the Light Mk.I/II in real time exercises. It was clear by 1935, in the context of the economical crisis, that only two main models would be kept for service, an infantry tank, slow but well-protected, and a cruiser tank, to exploit breakthroughs and attack deep behind enemy lines. The concept in itself already had been tested in 1918 with the Mark A Whippet, replaced by the Mark C and D, which were kept in service until the late twenties. But new technologies gave new solutions, and there were plenty of available mechanical parts on the market and suitable engines to make a cheap, fast, lightly protected, but well-armed model. With a tight budget, Vickers-Armstrong, the main tank supplier of the British Army, turned to its dream team and also hired John Carden to work on the project. However Carden died in a plane accident in December 1935, and when the final specifications came out, work on the plans had barely advanced.