Rhys-Davids gained his first victory on 23 May 1917 and began a steady run of success. Only two days later he gained his fifth air victory and became an ace. It was during the Third Battle of Ypres (July–November 1917) that Rhys-Davids scored the majority of his successes, gaining 22 more victories by the time of his death. On 23 September Rhys-Davids shot down the German ace Werner Voss (48 victories), who was killed; and possibly also Carl Menckhoff (39 victories). By 11 October 1917, Rhys-Davids had shot down five more enemy aircraft for an official total of 27 aerial victories – 23 of them individual kills.