On the night of February 24, 1942, an incident that has come to be called "The Battle of Los Angeles" erupted in the California sky. It happened less than three months after the U.S. had entered WW2.
An unidentified flying object was spotted, air raid sirens sounded, and a blackout was ordered. By the end of the "battle," over 1400 anti-aircraft shells (12.8 pounds each) had been fired at the object but the 37th Coast Artillery Brigade could not bring it down.
Several buildings were damaged by friendly fire, three civilians were killed by the anti-aircraft fire, and another three died of heart attacks attributed to the stress of the hour-long bombardment.
(I adapted this information from Wikipedia.)
Below are three videos about this incident. Please note that there are many more videos about The Battle of Los Angeles on YouTube if you care to search.