Co-writer Gale stated the plot is loosely based on what has come to be known as the Great Los Angeles Air Raid of 1941 as well as the bombardment of the Ellwood oil refinery, near Santa Barbara, by a Japanese submarine. Many other events in the film were based on real incidents, including the Zoot Suit Riots and an incident in which the U.S. Army placed an anti-aircraft gun in a homeowner's yard on the Maine coast.