in august 1914, when the war broke out, casey was working for the peninsular and oriental steam navigation company. on 25 may 1915 he was granted a temporary commission as a sub-lieutenant in the royal naval reserve, and on 30 may he was posted to for duty with the royal naval air service. on 27 may 1916 casey's royal naval reserve commission was cancelled, and the following day he was re-commissioned as a probationary flight sub-lieutenant in the royal naval air service. on 3 august 1916 he was confirmed in his rank of flight sub-lieutenant, with seniority from 28 may.