In April 1944, handing over command of the 2nd Armored Division to Major General Edward H. Brooks, he was designated chief of staff of the Third Army, serving again under Lieutenant General George Patton. Gaffey served in this capacity through the campaign in Western Europe, from the time the Third Army landed in France in July 1944 and played a major role in Operation Cobra and the Battle of the Falaise Gap, followed by the Allied advance from Paris to the Rhine and the Battle of Metz. In December 1944 he replaced Major General John Shirley Wood as CG of the 4th Armored Division, which played a major role in the Battle of the Bulge, helping to break the siege of Bastogne. He remained in command of the division until March 1945, towards the end of the war in Europe, when he became CG of the XXIII Corps. He relinquished command of XXIII Corps in September, when the war ended due to the surrender of Japan.