What happened when U.S. radar operators detected approaching aircraft on December 7, 1941?

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Pearl Harbor attack A U.S. battleship sinking during the Pearl Harbor attack.

On the morning of December 7, 1941, U.S. Army Private George Elliott was practicing on a mobile radar set—specifically an SCR-270—after its scheduled operating hours. During this time, he detected a large flight of approaching aircraft on the screen.12

When Elliott telephoned his lieutenant to report the observation, he was instructed to disregard the finding. The lieutenant assumed the radar had picked up a flight of B-17 bombers that was expected to arrive from the United States at that time. Consequently, the significance of the radar observation was not recognized until the Japanese attack began and bombs started to fall.12