Arabic numerals
The first mentions of the numerals in the West are found in the "Codex Vigilanus" of 976.
De Havilland Mosquito
Until the end of 1942 the RAF always used Roman numerals (I, II, ...) for mark numbers; 1943–1948 was a transition period during which new aircraft entering service were given Arabic numerals (1, 2, ...) for mark numbers, but older aircraft retained their Roman numerals. From 1948 onwards, Arabic numerals were used exclusively.