Pearl Harbor has always been portrayed as a surprise attack on an unsuspecting nation. And that, to a large extent, is true. The American people’s attention was focussed on the war in Europe, fearful that they would be dragged in. Already Roosevelt (Roosevelt, Franklin D.) was backing Britain against Hitler by supplying the UK with weapons under the Lend-Lease Act passed in March 1941. American shipping was in danger from attack by German submarines, the very thing that had brought America into World War I. And America had occupied Greenland and Iceland. Few Americans raised any concerns about the Sino-Japanese War which had been raging since 1937.
Whether the US administration was surprised by the attack on Pearl Harbor is another matter. A good case can be made that the US government knew of Japan’s plans, or should have. There were certainly indications.
On January 27, 1941, the Peruvian envoy in Tokyo told the third secretary in the US embassy that he had learnt from intelligence sources that the Japanese had a war plan which involved an attack on Pearl Harbor. On 10 July, the US military attaché in Tokyo reported that the Japanese Navy were secretly practicing airborne torpedo attacks on targets moored in Ariake Bay-a bay that resembles Pearl Harbor. The US military attaché in Mexico also reported that the Japanese were building midget submarines which would be towed to Hawaii for an attack on Pearl Harbor.
A top British agent, codenamed ‘Tricycle,’ told the FBI that the Japanese planned to attack Pearl Harbor, but his information was dismissed. And a Korean agent told American broadcaster Eric Severeid that the Japanese were going to attack Pearl Harbor. The agent repeated his story to a US Senator who alerted the State Department, US Army and Navy intelligence, and President Roosevelt personally.