While there may be no instances of German captured B-17's being used to attack American aircraft, There is a story of the Italian front where an Italian pilot reportedly did use a captured P-38 fighter (still in its USAAF markings) to attack American Bombers. One pilot who lost his plane and crew supposedly used a YB-40 (an up-gunned experimental B-17 with 16 x .50 MG vs 11 x .50 MG) painted with the known Italian pilot's wife's picture (she was in allied occupied territory) and as the story goes, enraged the Italian pilot over the radio with descriptions of making love to the woman. The Italian recklessly did a frontal attack to kill the American and wound up being shot down by the up-gunned bomber and was captured. He survived the war, the American was killed on a later mission. There are some disputes about the story and some sources report that no YB-40's were used in Italy but it is listed in many references as true.