Battle of Los Angeles

In the early hours of 25 February 1942, less than three months after Pearl Harbor and a day after a Japanese submarine shelled Ellwood near Santa Barbara, radar and observers reported an incoming raid and coastal anti-aircraft batteries fired more than 1,400 shells over Los Angeles for about an hour. No bombs fell, no aircraft were brought down, and five civilians died in accidents and heart attacks during the blackout. Navy Secretary Frank Knox called it a false alarm the same day. The Coast Artillery Association's 1949 account traced the first shots to a meteorological balloon released at 1:00 a.m., and the Office of Air Force History in 1983 attributed the event to war nerves, a lost weather balloon and stray flares and shell bursts. A heavily retouched Los Angeles Times photograph of searchlights converging on shell smoke later circulated as a picture of a craft.

Wartime false alarm triggered by a meteorological balloon and sustained by the barrage's own shell bursts and searchlights

• Wikipedia: Battle of Los Angelesen.wikipedia.org