Did FDR know about the Pearl Harbor attack before it happened?

The Japanese attack on the U.S. Naval Base at Pearl Harbor destroyed almost 200 U.S. aircraft, took 2,400 lives, and swayed Americans to support the decision to join World War II.

Within 24 hours, Congress had reversed its position of neutrality in World War II, declaring war on Japan and starting the chain of events that led to the U.S. forces joining the full war.

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Some claim there is evidence to suggest that President Franklin Roosevelt knew about plans for the attack in advance, and allowed it to happen specifically to justify entering the war.

Journalist John Flynn first emerged with the accusation in 1944.​

See images of the attack on Pearl Harbor:

Decades later in 1999, former sailor Robert Stinnett came forward with claims he'd uncovered evidence that the FDR administration deliberately provoked and allowed the Japanese to attack specifically to bring the U.S. into the war.

According to Stinnett the U.S. had cracked Japanese encryption codes years before the attack, therefore FDR knew about it. Those claims have been debunked by historians, who insist those codes were not yet deciphered.

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Stinnett also claimed U.S. intelligence would have been able to intercept radio signals from the Japanese planes crossing the Pacific, but former Japanese pilots have since testified that their planes were stripped of all equipment that would have been traceable, making them "radio silent."

There is some proof that Roosevelt had information suggesting there was a possibility of such an attack.

A memo released to the public in 2011, sent to Roosevelt three days before the 1941 attack, included warnings from naval intelligence that Tokyo was focused on Hawaii.

The declassified file included warnings from the Office of Naval Intelligence sent on December 4 that read in part, "In anticipation of open conflict with this country, Japan is vigorously utilizing every available agency to secure military, naval and commercial information, paying particular attention to the West Coast, the Panama Canal and the Territory of Hawaii."

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Additionally, diary entries by then-Secretary of War Henry Stimson reveal that he had a meeting with Roosevelt just ten days before the attack in which FDR pondered how to maneuver the Japanese into firing the first shot. Years later, Stimson revealed that the commanders at Pearl Harbor had been warned of the possibility of attack, and that he was surprised at how unprepared they were.

Ultimately, the majority of mainstream historians reject the idea that Roosevelt knew of the exact details of the Pearl Harbor attack, but also agree that the administration underestimated the threat coming from the Japanese empire.

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