Attack on Pearl Harbor: Why Weren't We Warned | HistoryNet

Questions abound as to why we did not know the Japanese were about to attack Pearl Harbor. We had cracked some of the codes most notably the diplomatic codes. Could it have simply been that we did not have enough certitude about the multiple Japanese codes in use? According to this article:

"The best intelligence came from breaking Japanese codes. Solving the secret messages of a hostile power is like putting a mirror behind the cards a player is holding, like eavesdropping on the huddles of a football team. It is nearly always the best form of intelligence. It is faster and more trustworthy than spies, who have to write up and transmit their reports and who are always suspected of setting up or falling for a deception. It sees farther into the future than aerial reconnaissance, which detects only what is present. It is broader in scope than the interrogations of prisoners, who know little more than what they have experienced. And it is usually cheaper and less obtrusive, hence more secret, than all of these. But it has a serious double-barreled failing: It cannot provide information that a nation has not put onto the airwaves, and its apparent omniscience and its immediacy seduce its recipients into thinking they are getting all the other nation’s secrets.

This is one of the lessons of Pearl Harbor. American code-breakers performed prodigies, giving remarkable insight into Japanese thinking. But that insight was not total, and so even the extraordinary U.S. cryptanalysis could not warn policymakers of Japan’s secret intentions. "