Street cars stop during the battle of Los Angeles, February 25, 1942

(From Wikipedia: The Battle of Los Angeles, also known as The Great Los Angeles Air Raid, is the name given by contemporary sources to the rumored enemy attack and subsequent anti-aircraft artillery barrage which took place from late 24 February to early 25 February 1942 over Los Angeles, California.

Initially, the target of the aerial barrage was thought to be an attacking force from Japan, but speaking at a press conference shortly afterward, Secretary of the Navy Frank Knox called the incident a “false alarm.”

Air raid sirens sounded throughout Los Angeles County on the night of 24–25 February 1942. A total blackout was ordered and thousands of air raid wardens were summoned to their positions. At 3:16 am the 37th Coast Artillery Brigade began firing .50 caliber machine guns and 12.8-pound anti-aircraft shells into the air at reported aircraft; over 1,400 shells would eventually be fired. Pilots of the 4th Interceptor Command were alerted but their aircraft remained grounded. The artillery fire continued sporadically until 4:14 am. The “all clear” was sounded and the blackout order lifted at 7:21 am.)