casey served in no. 2 wing, and was eventually posted to no. 3 (naval) squadron to fly the sopwith pup single-seat fighter. he gained his first aerial victory on 17 march 1917, driving down out of control a halberstadt d.ii fighter over bapaume. on 1 april casey was promoted to flight lieutenant, and gained his second victory a week later, driving down an albatros d.iii fighter on 8 april. he then gained seven more victories, six of them d.iii fighters, in only twelve days, from 21 april to 2 may. on 12 may he received a mention in despatches, and on 22 june was awarded the distinguished service cross. his citation read: