What does that matter, Spitfires were used from the very start escorting Fortress Is and B17s, they certainly did encounter opposition from the start, there were loses on both sides, it is a gross insult to the men who were lost to say it never happened. By the time the P-47 was used as a second wave escort taking over from Spitfires as the first wave the USA had been mounting bombing operations for a long time.Johnny Johnson mentioned numerous times in his writings of fly around empty skies and his squadron was elated when they finally got aux tanks in their MkXIV's and flew across the border into Germany for the first time.