Beginning in 1941, he commanded Atlantic Fleet Task Groups in neutrality patrols and convoys until becoming Commander, Amphibious Force, Atlantic Fleet, in April 1942. This force, also called Task Force 34, became the U.S. component of the Operation Torch landings in November 1942. Hewitt was then assigned as Commander, U.S. Naval Forces, Northwest Africa Waters or COMNAVNAW. (Sean Maloney, To Secure Command of the Sea, thesis, 1991, p.25) Hewitt remained in this post until 1945, when he chaired a Pearl Harbor investigation.
Following World War II, he commanded U.S. Naval Forces Europe, advised the Naval War College, and served as a Navy representative to the United Nations. Hewitt retired from active duty in 1949.