1943 -- 48 was a transition period during which new aircraft entering service were given Arabic numerals for mark numbers but older aircraft retained their Roman numerals .
Up until the end of 1942 , the RAF always used Roman numerals for mark numbers .
1943 -- 48 was a transition period during which new aircraft entering service were given Arabic numerals for mark numbers but older aircraft retained mark numbers ' Roman numerals .
Up until the end of 1942 , the RAF always used Roman numerals for mark numbers .