The number to be produced was subject to fluctuation as the War Office vacillated in their demand ; in July 1938 , it requested that 70 of the tanks be produced , then increased the request to 120 after a three @-@ day conference in November . Production was to begin in July 1940 , but meanwhile the War Office temporarily returned to its original order of 70 before increasing the number to 100 . The number further increased to 220 after Metropolitan Cammell Carriage and Wagon , a company part owned by Vickers @-@ Armstrong that would be producing the tanks , indicated it had already ordered armour plating for that many tanks .