What could the major powers do with their pre-war dream fleets if those fleets appeared during the war?
Short answerThe outcome depends on the power because fuel, industry, operating doctrine, and technological maturity matter as much as raw ship numbers.
NotesA magically completed fleet would affect each belligerent differently. Full fuel tanks would matter especially to Germany and Italy, while Japan still faced the problem of moving Dutch East Indies oil home. German and Japanese paper plans would also produce equipment that their wartime economies had never brought to maturity. Britain's early radar-integrated destroyer reflects the timing of its design cycle rather than a simple national technology gap. The counterfactual exposes the industrial, logistical, and doctrinal systems hidden behind fleet lists.