The incident in which Sismey was wounded occurred on 18 May 1942, when he was the co-pilot of a Consolidated Catalina flying boat flying over the Mediterranean, off Oran, French Algeria. The Catalina ("AJ158"; callsign "F") was assigned to No. 202 Squadron, Royal Air Force (RAF), based at Gibraltar. It was attacked by three Dewoitine D.520 fighters belonging to "Groupe de Chasse III/6" (GC III/6) of the Vichy French Air Force. Sismey received multiple wounds in his back from shrapnel – metal fragments of his own aircraft and/or French ammunition. The crew managed to make a forced landing on the sea, after which the Catalina sank. Further attacks by French aircraft were fended off by Fairey Fulmar fighters from the aircraft carrier , and the crew of a Short Sunderland, commanded by Flight Lieutenant Graham Pockley, from No. 10 Squadron RAAF. The Catalina crew spent eight hours in the sea, and Sismey was unconscious by the time they were picked up by the British destroyer HMS "Ithuriel". Nevertheless, all of them survived the incident.