No, FDR did not know the Japanese were going to bomb Pearl Harbor

Seventy-five years after the Japanese attack on Pearl Harbor, some Americans have never stopped believing that President Franklin Roosevelt let it happen in order to draw the U.S. into World War II.

"It's ridiculous," says Rob Citino, a senior researcher at the National World War II Museum in New Orleans. "But it's evergreen. It never stops. My students, over 30 years — there'd always be someone in class [who'd say], 'Roosevelt knew all about it.'"

Conspiracy theories, half-truths and full-on lies are getting new attention as they appear alongside real news and information on social networks — but that's nothing new. The official investigations into the Japanese attack started in the 1940s, and even now, each time new documents become declassified, a headline pops up asking whether Roosevelt allowed it.

No, says Roosevelt biographer Jean Edward Smith.

"He was totally caught off guard by it," Smith says. "The record is clear. There was no evidence of the Japanese moving toward Pearl Harbor that was picked up in Washington."

That's not to say that the White House might not have expected some kind of attack from Japan — possibly against U.S. bases in the Philippines. Roosevelt had been tightening the screws on Tokyo to hinder the Japanese conquest of China, "instituting a full embargo on exports to Japan, freezing Japanese assets in U.S. banks and sending supplies into China along the Burma Road," according to the State Department.

Citino says Roosevelt believed those economic restrictions could get Japan to reduce its ambitions in Asia.

"Sanctions are better than war — if you have time to let them apply, and if there's somebody sensible on the other side." But Roosevelt "was wrong in that assessment," Citino says, and the Japanese were mistaken in thinking they could remove the threat from the U.S. Navy to their operations in the Western Pacific.

"Pearl Harbor [brought about] unintended consequences for both sides," he says.

The U.S. didn't think the Japanese would retaliate militarily. And the use of then-new naval weapons such as aircraft carriers was still being explored. No one had sailed a fleet of carriers 4,000 miles across an ocean to raid an enemy's fleet while it sat at anchor.

For their part, the Japanese did not think the U.S. would have the stomach to rebuild its Navy and then launch a bloody fight, island by island, across the Pacific.

These kinds of bad assumptions and poor intelligence start wars, Citino says — an understanding that seems so obvious today even as the conspiracy theories outlive the eyewitnesses to the battle. Copyright 2019 NPR. To see more, visit https://www.npr.org.