From the outset of his legal career, many commented on his ability as a lawyer, particularly in criminal defence. After a period, Bushell was appointed to military cases in prosecuting RAF personnel charged with various offences. These often involved pilots charged with dangerous flying. In October 1939, acting as assistant to Sir Patrick Hastings, he successfully defended two RAF pilots, John Freeborn and Paddy Byrne, court martialled after the friendly fire incident known as the Battle of Barking Creek. Byrne would later be incarcerated with Bushell at Stalag Luft III. Bushell was given command of No. 92 Squadron in October 1939. His promotion to squadron leader was confirmed on 1 January 1940. During the squadron's first engagement with enemy aircraft on 23 May 1940, while on a patrol near Calais, to assist with the Dunkirk evacuation, he was credited with damaging two Messerschmitt Bf 110 fighter aircraft of ZG 26 before being shot down himself, probably by future ace "Oberleutnant" Günther Specht. He crash-landed his Spitfire on German-occupied ground and was captured before he had a chance to hide. Bushell became a prisoner of war and was sent to the Dulag Luft transit camp near Frankfurt with all the other captured aircrew. On arrival at Stalag Luft he was made part of the permanent British staff under the senior British officer Wing Commander Harry Day. The permanent staff's duty was to help newly captured Allied aircrew to adjust to life as a prisoner of war. Escape, which was regarded as an important duty of all prisoners of war of officer rank, was never far from his mind and, fortunately, he was in good company with Day and Fleet Air Arm pilot Jimmy Buckley. Day placed Buckley in charge of escape operations, with Bushell as his deputy. The three of them formed the escape committee responsible for all escape attempts. The permanent staff of the camp started several escape tunnels, one of which was completed in May 1941. Bushell was given a place in the tunnel, but elected to escape on the same day as the tunnel break by cutting through the wire surrounding a small park in the camp grounds. His decision for not using the tunnel was to allow him an earlier get away, thus enabling him to catch a particular train. The exact date of the escape is not known, but is believed to have occurred in June 1941. Bushell hid in a goat shed in the camp grounds and, soon as it was dark enough, he crawled to the wire and made good his escape.