William Roy Irwin joined the
Canadian Expeditionary Force On 22 November 1917, probationary
second lieutenant W. R. Irwin was appointed a
Flying Officer. This date also marked his later postdated promotion to
lieutenant. Once assigned to 56 Squadron at the combat front in France, Irwin flew his first patrol on 1 March 1918, as a
Royal Aircraft Factory SE.5a pilot. He joined the war even as the Germans launched their last great offensive of the war. Irwin would not score again until 8 August 1918, when he destroyed a
Fokker D.VII northeast of
Chaulnes. He would proceed to score five more victories over Fokker D.VIIs that month. He destroyed two of them on the morning of 10 August and drove down another out of control in the evening; two days later, he destroyed another pair. Irwin destroyed another pair of Fokker D.VIIs on the morning of 3 September 1918, rounding out his total tally at nine enemy planes destroyed and two driven down out of control. However, on 15 September, he pounced on a decoy two-seater and was in turn jumped by four enemy fighters. He was
wounded in action during the dogfight, but escaped. It was while he remained in hospital on 23 September that he was awarded a Bar in lieu of a second award of the DFC. Shortly thereafter, Irwin was discharged from hospital and assigned to instructor duty at the
Central Flying School in
Upavon. The war ended while he was in this assignment. ==Between the World Wars==