Posted to Britain in April 1944, Barr went ashore at Omaha Beach two days after D-Day as part of an air support control unit. During the campaign in Normandy, he flew rocket-armed Hawker Typhoons on operations against V-1 flying bomb launch sites. After his return to Australia on 11 September, Barr was promoted to acting wing commander and appointed chief instructor at No. 2 Operational Training Unit in Mildura, Victoria, taking over from Bobby Gibbes. He also went to New Guinea and flew some ground-attack missions in the Kittyhawk to gain experience in the South West Pacific theatre. Following the end of hostilities in August 1945, Barr was treated for recurring fever and underwent two operations on his limbs in No. 6 RAAF Hospital, Heidelberg. He was discharged from the Air Force on 8 October.