Watson underwent his aviation training while still in Canada. He was posted overseas to France in 1917. On 13 August 1917, Watson was commissioned as a
second lieutenant in the
Royal Flying Corps. He trained as a fighter pilot and was initially assigned to
No. 28 Squadron in Italy. However, Watson would not achieve his first aerial success until after his transfer to
No. 70 Squadron in France. After becoming an ace on 8 October, he scored two victories the following day. In an extraordinary feat, he singlehandedly drove down a
Fokker D.VII and its German pilot into captivity and simultaneously cooperated with four other British pilots in a second capture of a D.VII and pilot. Watson earned the Distinguished Flying Cross for his valor, though not for the twin captivities. The DFC would not be promulgated until after war's end. ==List of aerial victories==