In February of 1942, only a few months after the United States entered World War II, an unexplained and mysterious incident took place in the skies over Los Angeles, California. A number of unidentified flying objects were sighted, moving at speeds both very fast and very slow, and thousands of anti-aircraft shells were fired at what was thought to be Japanese aircraft. Not one of the objects was shot down, and no explanation could be given as to just what the objects were. Many felt that the objects were airplanes, but still others feel that the objects were in fact UFOs.
Read full article on Wikipedia: Battle of Los Angeles