'Kraut fireball' German-secret-weapon theory.
discreditedcompeting_explanationScandinavian "ghost rockets"
The wartime fear that foo fighters were a secret German (or Japanese) weapon; announced in a SHAEF press release (13 Dec 1944).
Discredited as fact: Axis pilots reported the same phenomenon, the objects never behaved as weapons (no attack, no damage), and no such device was found in captured materiel after the war.