 There were several variants of the Tetrarch design . The first was the Light Tank Mk VIII , Vickers @-@ Armstrong 's proposed successor to the Tetrarch . The Mark VIII was also known as the Harry Hopkins , named after President Roosevelt 's chief diplomatic advisor , and was given the General Staff design number A25 by the War Office . The Mark VIII was intended to improve upon the design of the Tetrarch in a number of areas . It had thicker armour than the Tetrarch , with the front hull and turret armour increased to a thickness of 38 millimetres ( 1 @.@ 5 in ) and the side armour to 17 millimetres ( 0 @.@ 67 in ) , and the turret and hull given more sloped surfaces to help deflect shells fired at the tank . The dimensions of the Tetrarch were also changed ; the Mark VIII was longer by 6 inches ( 0 @.@ 15 m ) , wider by 1 foot 3 inches ( 0 @.@ 38 m ) and heavier . The new tank was no longer air @-@ portable , as it was too heavy to be carried by a Hamilcar . The 12 @-@ cylinder engine of the Tetrarch was fitted to the Mark VIII , although the increased weight meant that its maximum speed decreased to 30 miles per hour ( 48 km / h ) ; its armament also remained the same as that of the Tetrarch . The War Office authorised the construction of three prototype models in April 1941 . The new design was considered a success , and the Tank Board of the War Office ordered 1 @,@ 000 to be constructed in September . However , problems were encountered with further tests of the prototypes , and a report issued in December 1942 stated that production of the Mark VIII had been delayed due to developmental problems . These problems continued to persist into 1943 , when the War Office decided against using the tank in active service ; approximately 100 Mark VIIIs were produced by 1945 , when production ended . 
