During World War II, Allied pilots over Europe and the Pacific reported seeing blobs of light or fire near their planes. In 1945, Time reported:

If it was not a hoax or an optical illusion, it was certainly the most puzzling secret weapon that Allied fighters have yet encountered. Last week U.S. night fighter pilots based in France told a strange story of balls of fire which for more than a month have been following their planes at night over Germany. No one seemed to know what, if anything, the fireballs were supposed to accomplish. Pilots, guessing it was a new psychological weapon, named it the “foo-fighter.” … Their descriptions of the apparition varied, but they agree that the mysterious flares stuck close to their planes and appeared to follow them at high speed for miles. One pilot said that a foo-fighter, appearing as red balls off his wing tips, stuck with him until he dove at 360 miles an hour; then the balls zoomed up into the sky.

Possibly they were electrical discharges, like St. Elmo’s fire, or possibly German anti-aircraft batteries were firing flares to aid their night fighters. Whatever they were, the lights apparently caused no injury or damage.