After the United States entered World War II, Ballentine served as the second commanding officer of the escort carrier USS "Long Island" from 26 December 1941 to 18 April 1942. He was promoted to captain on 30 June 1942. Ballentine served as chief of staff to Task Group 34.2 commander Rear Admiral Ernest D. McWhorter aboard during the Allied invasion of French North Africa in November 1942.