Then World War II intervened – leading to the line being renamed, briefly and abortively, the "Kitchener Kids" due to anti-German sentiment – and Dumart enlisted with teammates Schmidt, Bauer and Frank Brimsek. Joining the Royal Canadian Air Force halfway through the 1941–42 season, Dumart joined the Ottawa RCAF Flyers hockey team which challenged for the Allan Cup, Canada's senior league championship, and scored over a goal a game in leading the team to the title. He played briefly in the fall of 1942 for the Flyers before being shipped overseas, where he served until the end of the war.