On September 12, 1942, the 71, 121, and 133 Squadrons were "activated" as the USAAF's 4th Fighter Group, operating from a former RAF field at Debden. After a few months flying Spitfires, the group was re-equipped with the new Republic P-47 Thunderbolt. On April 15, 1943 Blakeslee claimed an Fw 190 for the group's first P-47 "kill", and claimed a further Fw 190 on May 14, 1943, both near Knocke. Leading the 335th Squadron of the 4th FG, Blakeslee flew the group into Germany for the first time on July 28. Towards the end of the year, Blakeslee led the group more often, and developed a tactic of circling above any air battle and directing his fighters as necessary.