Cruiser Mk I 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 . The Cruiser Mk II was a heavier armoured adaptation of the Mark I developed at much the same time . Design and development . In 1936 the British War Office designated two different kinds of tanks for future development : heavily armoured infantry tank s to be used in close co - operation with infantry during attacks , and fast mobile cruiser tanks designed to make forays deep into enemy territory . In 1934 Sir John Carden of Vickers - Armstrong was asked to provide a " reasonably cheap tank " as a replacement for some of the mediums then in use . The pilot model of his design was finished in 1936 and given the designation A9E1 . It incorporated the best features of the earlier Mk III Light Tank , and was powered by a commercial petrol engine . However , this was still in the time of the Great depression and the tank had a number of cost - cutting measures applied . It was the first British tank to have a centrally located turret and to have powered traverse . The system was by Nash & Thompson and similar to that being introduced on the Vickers Wellington bomber aircraft . The armour was light with a maximum of 14 mm thickness , many armour faces were vertical , and there were numerous shot traps but it could achieve 25 mph and carried the new high velocity 2pdr gun . The driver ' s compartment and the fighting compartments were not separated . As well as the turret armament , which consisted of a QF 2 - pounder ( 40 mm ) gun and a coaxial Vickers machine gun , there were two small turrets either side of the driver ' s compartment , each sporting one more machine - gun . Both these smaller turrets were permanently manned , which gave the tank a total crew of 6 ( Commander , gunner , loader , driver and two machine - gunners ) . The A9E1 was tested against other designs and - although lacking in some areas - in 1937 it was accepted as an interim design until a Christie suspension cruiser tank could be delivered . An order was placed for 125 . Seventy - five were built by Harland and Wolff , and the other 50 were built by Vickers . Originally a Rolls - Royce car engine was used , but this proved underpowered and was replaced by an AEC bus engine . The later Valentine Infantry tank essentially used the same lower hull and suspension , though with considerably more armour . The A9 weighed 12 tons , was 5 . 8 metres long , 2 . 65 metres high , 2 . 5 metres wide , and had a top speed of 25 mph on road and 15 mph off . Its maximum road range was 150 miles . The ammunition load was 100 2 - pounder rounds and a total of 3 , 000 rounds for the three Vickers machine guns . Service . The Mark I cruiser began to be delivered in January 1939 . The Cruiser was an effective tank in the French , Greek and early North African campaign s . The 2 pdr gun was lethal against the early Italian tanks encountered during the North African campaign and could hold its own against Rommel ' s early Panzer IIs and IIIs . The A9 ' s 2 - pounder gun could also breach the 20 – 30 mm of protective steel on later opponents such as the Panzer III " ausf " D and the Panzer IV " ausf " D variants . It was effective until the Germans introduced the more thickly armoured Panzer IV " ausf " E variant to the desert in Spring 1941 . However , the minimal armour made the A9 an easy kill for most Axis anti - tank weapons . Also problematic was the lack of High Explosive shells for the 2 pdr gun and even worse the lack of AP for the 95 mm gun on the Close Support version . Another issue was that the areas around the front machine gun turrets created a frontal surface that was more vulnerable to enemy fire than it would have been had it been a flat plate , let alone a sloped glacis . The mechanical unreliability of the Cruiser was also a disadvantage . In particular , tracks were easily slewed causing difficulties .