The Tetrarchs remained in Britain , and would probably have been used as training vehicles before being retired from service , but on 22 June 1941 the German invasion of the USSR , Operation Barbarossa began , and the USSR became an ally of Britain . The Lend @-@ Lease program , begun in March 1941 by the United States of America to supply defensive materials to Britain and China , was therefore extended to the USSR . As part of the program , the British government began supplying war materials to the USSR , which in early 1942 , included a shipment of 20 Tetrarchs , as well as a number of Valentine and Matilda Mk I Infantry tanks . The Soviet military utilised a greater number of light tanks than the British , and so could use the Tetrarchs . When the tanks arrived in the USSR , however , it was apparent that the design problems with the cooling system were also present in cold conditions ; additionally , the cold weather had a deleterious effect on the tank 's suspension and tracks . Additional testing of the Tetrarchs was conducted by the Soviet military and the design was admired for its controllability , manoeuvrability , and speed , as well its ability to run on low @-@ quality fuel , unlike contemporary Soviet designs . The thinness of the Tetrarch 's armour was found to be a problem and one which could not be solved , as the weight of extra armour plating caused an unacceptable reduction in the tank 's speed . Despite these drawbacks in the Tetrarch 's design , Soviet authorities believed it to be comparable to the T @-@ 70 light tank in use at the time , and decided that it was suitable to be used in combat . A number of Tetrarchs were sent to Tank Training Schools which were subsequently sent into battle , and in September 1943 two were assigned to the 132nd Separated Tank Battalion , which was attached to the 5th Guards Tank Brigade ; both tanks were destroyed in combat , one on 30 September and the other on 2 October , the latter a casualty of artillery fire . Several were also used for propaganda purposes , appearing in photographs of Soviet troops who were fighting in the Caucasus region .