The Battle of Los Angeles
After Pearl Harbour, everyone was understandably paranoid about further attacks. On Feb 25/42, radar and eyewitnesses picked up enemy fighters near LA and anti-aircraft guns started firing at 3 AM.
After it was all over, there were over 1,400 rounds fired, but nothing was hit. There were no signs of any enemy fighters, and the Japanese later confirmed that they never launched an attack on LA.