At Disney, McDermott worked as an in-betweener and effects animator on "Brave Little Tailor", "Pinocchio", "The Reluctant Dragon" and "Fantasia". His experiences while working at Disney, particularly during the time of the 1941 Disney animators' strike, would later become the basis for his 1969 satirical novel "The Rat Factory". McDermott left Disney to fight with US forces during World War II.