Lewis Hancock Jr. was born on 15 October 1889 in Austin, Texas. He was appointed to the United States Naval Academy from that state in 1906 and graduated in June 1910. He served on the battleship before being commissioned as an Ensign in March 1912, then underwent submarine instruction and served in the new submarine . Between 1913 and 1915 Ensign Hancock commanded the submarine . Promoted to Lieutenant (junior grade) in 1915, he was Commanding Officer of the submarine between 1916 and 1918, receiving the Navy Cross for "distinguished service" during World War I combat operations against German U-boats. Later in 1918 Lieutenant Commander Hancock commanded another submarine, . He also had wartime and post-war tours as a machinery inspector.