Irish citizens were free to work abroad and join foreign militaries. By the end of the war, figures suggest that 50,000 men and women born in the State served in the British armed forces, although this estimate has risen considerably over the years. One Irishman, Brendan Finucane, the youngest Wing Commander and fighter ace in the RAF's history, before the age of 22 achieved one of the highest kill rates in the Battle of Britain and in offensive operations over France.