In 1944 RAF air crew operating over Europe at night reported seeing mysterious glowing balls that followed their aircraft, swooping and diving around the night sky at amazing speeds. At first it was thought the objects were some kind of German secret weapon. They were dubbed foo fighters by the air crew, who tried to shoot them down or manoeuvre away from them - but always without success. After the war it was discovered that the Germans had also encountered the foo fighter, but had thought they were British secret weapons.
from The Little Book of the Paranormal by Rupert Matthews