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Ok so the basic premise is an American sub on patrol spots the Japanese fleet thus warning the Americans of the impending attack. The idea revolves around either the Japanese striking against prepared American defenses or the Americans attacking the Japanese fleet before it has a chance to launch the attack. Now lets say the Americans are able to strike the Japanese and catch them off guard before they launch their carrier based craft and sink a carrier or two, plausible? Or the Japanese planes flying into a prepared American defenses, plausible?

Now if this is plausible, what would be the effects of the Americans catching the Japanese fleet off guard? Or atleast stopping their air attack on Pearl Harbour?
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