The British RAF first reported these phenomena during missions to bomb Germany in March 1942, with American sightings beginning in October 1944 over occupied Belgium. At the time, they were erroneously believed to be Messerschmitt Me 163 rocket-powered interceptors (those first flew in September 1941, but never operated at night).
The objects were variously described as fiery, and glowing red, white, or orange. Some pilots described them as resembling Christmas-tree lights and reported that they seemed to toy with the aircraft, making wild turns before simply vanishing. Pilots and aircrew reported that the objects flew together in formation with their aircraft, behaving as if they were under intelligent control, never displaying hostile behaviour, but could not be outmaneouvered or shot down. The initial fear that that they might be secret German weapons was largely discounted when it became apparent that German and Japanese pilots were also reporting similar phenomena. Speculation continued that they might be related to the ‘fire balloons’ later employed by the Japanese to carry bombs in the jet stream across the Pacific to North America.
The British Air Ministry was asked if it had any intelligence information and replied on 13 March 1945: “
Bomber Command crews have for some time been reporting similar phenomena. A few of the alleged aircraft may have been Me 262 and for the rest, flak rockets are suggested as the most likely explanation. The whole affair is still something of a mystery and the evidence is very sketchy and varied so that no definite and satisfactory explanation can yet be given.”
In 1994, author Renato Vesco revived the wartime theory that the foo fighters were a Nazi secret weapon; a form of ground-launched, automatically guided, jet-propelled flak mine called the ‘Feuerball’ (Fireball). The devices were supposedly operated by special SS units, resembled tortoise shells in shape, and flew by means of gas jets that spun like a Catherine wheel around the fuselage. He claimed that miniature klystron tubes inside the devices, in combination with the gas jets, created the characteristic glowing spheroid appearance, and a crude form of collision avoidance radar ensured they would not crash into other airborne objects, also having an onboard sensor to instruct the devices to depart swiftly if fired upon. According to Vesco, the devices were intended to have a distracting and disruptive effect on bomber pilots, and also had an offensive capability via electrostatic discharges to interfere with ignition systems of aircraft and cause their engines to stall. The evidence for his claims is virtually non-existent and dismissed as ‘nonsense’ by most experts.
Various types of electrical discharge have been suggested as possible explanations. ‘St. Elmo's Fire’ has been known to appear at the wingtips of aircraft, and some of the descriptions of ‘foo fighters’ also closely resemble those of ‘ball lightning’.