That led to his most famous exploit, in which he masqueraded as Cyr, working as a trauma surgeon aboard HMCS "Cayuga", a Royal Canadian Navy destroyer, during the Korean War. He managed to improvise successful major surgeries and fend off infection with generous amounts of penicillin. His most notable surgical practices were performed on some sixteen Korean combat casualties who were loaded onto the "Cayuga". All eyes turned to Demara, the only "surgeon" on board, as it became obvious that several of the casualties would require major surgery or certainly die. After ordering personnel to transport these variously injured patients into the ship's operating room and prep them for surgery, Demara disappeared to his room with a textbook on general surgery and proceeded to speed-read the various surgeries he was now forced to perform, including major chest surgery. None of the casualties died as a result of Demara's surgeries. Apparently, the removal of a bullet from a wounded man ended up in Canadian newspapers. One person reading the reports was the mother of the real Joseph Cyr; her son at the time of "his" service in Korea was actually practicing medicine in Grand Falls, New Brunswick. When news of the impostor reached the "Cayuga," still on duty off Korea, Captain James Plomer at first refused to believe Demara was not a doctor (and not Joseph Cyr). However, faced with the embarrassment of having allowed an impostor into the navy's ranks, Canadian officials chose not to press charges. Instead, Demara was quietly dismissed from the Royal Canadian Navy and forced to return to the United States. The "MASH" episode "Dear Dad... Again" included a one time character Captain Adam Casey, likely inspired by Demara's exploits, who performs several surgeries, but turns out not to be a real doctor.