[2][3] On finishing school, he applied for a short service commission and joined the Royal Air Force as a flight cadet at the RAF College Cranwell passing out as an acting pilot officer on 1 August 1936.

Tasked with a reconnaissance mission over the Wesel-Bocholt area of Germany, Casey took off from the airfield at Etain at 1100 hours on 16 October 1939 flying a Bristol Blenheim Mark I (serial L1141).

[10] A Luftwaffe Messerschmitt Bf 109 flown by Leutnant Hans-Folkert Rosenboom[11] of Jagdgeschwader 1 (Fighter Wing 1) intercepted the Blenheim and, after a long chase sometimes only 6 feet from the ground, shot it down near Lingen.

[17] While held at Barth, Casey was one of a group of prisoners known as "ghosts" who hid from the Germans within the camp for extended periods and did not attend the roll calls to give the impression that they had escaped.

[18] Casey was a member of the group of "bad lads" with Bushell who were sent to the reputedly escape proof Stalag Luft III in the province of Lower Silesia near the town of Sagan (now Żagań in Poland).

[1] For the Great Escape operation, Casey was the treasurer, head of filing and, most importantly, arranged safe concealment of forged documents in caches around the camp avoiding the repeated and intensive German searches.

[27] The Glasgow Herald of 19 May 1944 published an early list naming several officers, including Casey[28] His conspicuous bravery as a prisoner was recognised by a mention in despatches as none of the other relevant decorations then available could be awarded posthumously.