1945.01.02
The New York Times of 2 January 1945 reported several other cases of foo-fighters seen over France over a period of several months.
(UFOs 1947-1987: The 40-Year Search for an Explanation, Evans and Spencer)
On 2 January 1945, stories appeared in the press in many countries, using the term “foo fighter” and still implying a weapon, but adding that nobody could identify what it was.