On 16 April 1944 the group moved to RAF Wormingford to accommodate the arrival of the 398th Bomb Group. The 55FG converted to North American P-51D Mustangs in July 1944, continuing their primary task of escorting B-17 and B-24 bombers that attacked such targets as industries and marshalling yards in Germany, and airfields and V-weapon sites in France. In July the group attacked gun emplacements during the Saint-Lô breakthrough in July 1944, and transportation facilities during the Battle of the Bulge, December 1944 – January 1945. The group also patrolled the air over the English Channel and bombed bridges in the Tours area during the invasion of the Continent in June 1944. The unit patrolled the Arnhem sector to support the airborne invasion of the Netherlands in September 1944 along with strafing trucks, locomotives, and oil depots near Wesel when the Allies crossed the Rhine in March 1945.