AN EIGHTH BOMBER STATION, Dec. 30 -- The Luftwaffe apparently is mixing veteran fighter pilots with inexperienced airmen to train interceptor squadrons, Flying Fortress crews reported after today's raid on Germany.
    Formations of four or five German planes would hover outside the range of the bomber's guns, crewmen said, while one pilot, apparently a veteran from his skilled aerobatics, would barrel-roll into the center of a B17 group, where Fortress gunners could not fire at him without endangering other bombers.
    Barrel-rolling back out, the leader then would bring the entire formation of Nazi fighters into the bomber group, firing as they came, according to 1/Lt. Mack G. Hemphill, of Jackson, Miss.