The War Office and the Army were concluding , at this point , that light tanks were a liability and too vulnerable for use in further combat , and the Tetrarch was considered to be obsolete . This decision may have marked the end for the Tetrarch in active service ; several of the tanks destined to be deployed to the Eighth Army in the Middle East for the North African Campaign were left in Britain when their cooling systems were determined to be unable to cope with the intense North African heat .