Foo Fighters
No, not the band. World War II had a tremendous amount of unexplained phenomena, but one of the most common was “foo fighters.” These inexplicable colored lights appeared to literally hundreds of Allied fighter pilots over the course of the war, first in 1944. They were described as blazing ovals of white, red and orange fire that moved erratically at airplane heights, often flying alongside planes before suddenly curving off. They were taken very seriously by the Allied command, who feared that they were some kind of Axis secret weapon. Although several theories were floated, none were proven, and they remain a mystery to this day.