Strange objects, which American pilots called "foo-fighters," were seen over Germany and occupied France during World War II. As soon as the war was over, they disappeared from the skies. These objects were also reported over Japan. Here is a look at what may have happened and what the objects really were:
The name "foo-fighters" gives a clue. The legend says the name came from the Smokey Stover comic strip. Smokey Stover (a fireman) always said, "Where there's foo, there's fire." It came from the French word for fire, "feu" (pronounced "foo"). That may indicate that the objects were really feu-fighters - type-1 fire balloons launched by the French Underground.
The top brass (who knew what they were) probably used the name "feu-fighters," and the ranks (who didn't know what they were) heard "foo-fighters." One could also think of them as being "faux-fighters" (faux, pronounced "foe" means "fake"). But then they would have been heard as "foe-fighters." "Foo-fighters" was safer because it did not tip off the Germans.
The fire balloon would have been a wonderful weapon for the French Resistance to use on the Germans. The materials were innocuous items used in daily life, and it was easy to conceal a constructed balloon as a roll of tissue paper or a party lantern. Once launched, they quickly lost their identity as hot-air balloons in the night sky. The German High Command would have been confounded by moving lights in the night sky with these strange properties:
The Germans were too sophisticated to believe that pieces of tissue paper were the remains of crashed aircraft. They would have either thought the witness was lying, or the tissue paper had just blown away from somewhere and the witness was confused. It looks like a paper lantern, and could be one if turned upside down.
These weapons had two tactical purposes as well as the psychological one:
The foo-fighters seen over Japan have another cause. Most of these were the planet Venus. In the closing year of the war, it was first in the western sky, hanging right over Japan as seen by the crews of bombers approaching from the east. "They" also seemed to follow the planes back to their bases after a bombing run. Later in the year, Venus was in the eastern sky. Many times, edgy gunners cut loose a few rounds at Venus, then caught themselves. In a little overcast, Venus would be harder to identify, and might suddenly disappear. The Japanese also had their own version of the fire balloon.
The stories of foo-fighter sightings were probably brought to the Pacific theater by pilots who were transferred there after VE-day. They naturally thought they were seeing the same thing. Some undoubtedly were. Venus also can explain some foo-fighters seen over the English Channel. Some pilots probably thought Venus was a foo-fighter, after hearing other pilots describe fire balloons.
With a little thought, prosaic explanations become the most probable ones here. I seem to remember seeing a movie where the French Underground launched balloons to fool the Germans.
ADDENDUM: Japanese subs launched fire balloons in 1942 off the California coast. One of the "Fu-Go" flying bombs caused the Battle of Los Angeles on 2/25/1942 (Called a UFO case by some). Antiaircraft batteries, thinking the Fu-Go was a plane or a blimp, shot at it. They blew it up, but couldn't tell that explosion from the flak they were sending up. These balloons also caused minor damage when they hit something. And people are still finding crashed, but unexploded Fu-Gos in the mountains of California and Nevada.