 Mosley was a fencing champion in his school days; he won titles in both foil and sabre, and retained an enthusiasm for the sport throughout his life.In January 1914, Mosley entered the Royal Military College, Sandhurst but was expelled in June for a "riotous act of retaliation" against a fellow student.During the First World War he was commissioned into the British cavalry unit the 16th The Queen's Lancers and fought in France on the Western Front.