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Original radar plot of Detector Station Opana, Pearl Harbor, Hawaii, December 7, 1941

Beginning at 7:02 a.m., December 7, 1941, two U.S. Army radar operators in Oahu detected and plotted unusual air activity approaching the island. An officer dismissed the information, speculating that U.S. military planes were patrolling the area. The joint committee investigating the Pearl Harbor attack used the radar plot as evidence of a failure of military intelligence communication.

Records of Joint Committees of Congress, National Archives and Records Administration

Original radar plot of Detector Station Opana, Pearl Harbor, Hawaii, December 7, 1941

The Pearl Harbor Attack

On December 7, 1941, Japan attacked the United States Pacific Fleet at Pearl Harbor, Hawaii, killing thousands and destroying U.S. military ships and planes. Congress declared war against Japan the following day. At the end of the war, after seven military and presidential investigations had identified different reasons for the lack of U.S. preparedness at Pearl Harbor, Congress created a joint committee to review possible lapses in intelligence. Its findings led Congress to pass the National Security Act of 1947 to modernize national security agencies and coordinate military readiness.

The completely ineffective liaison between the Army and the Navy in Hawaii at a time when the fullest exchange of information was absolutely imperative dictates that military and naval intelligence, particularly, must be consolidated.

Pearl Harbor Committee, Investigation of the Pearl Harbor Attack, July 20, 1946