On February 24–25, 1942, the U.S. Army fired more than 1,400 anti-aircraft shells over Los Angeles after radar operators and ground observers reported unidentified objects; five civilians died in the chaos, and no enemy aircraft or debris was ever recovered.

Secretary of the Navy Frank Knox called it a 'false alarm' the next day. The 1983 U.S. Office of Air Force History attributed the trigger to 'war nerves' and a lost weather balloon. An AP photograph of searchlight beams converging on an unidentified shape ran on front pages nationwide.