In 1934 he was promoted to lieutenant, then "invalided out," permanently disabled by tuberculosis. During January and February 1936, Roper moved north for operations in Alaskan waters. In February 1937, Roper departed California and, after transiting the Panama Canal, joined the Atlantic Fleet. For the remainder of the year, through 1938, and into 1939, she conducted exercises primarily off the mid-Atlantic seaboard and, during part of each year, in the Caribbean. In November 1939, after the outbreak of World War II in Europe, she shifted from Norfolk, Virginia, to Key West, Florida, whence she patrolled the Yucatán Channel and the Florida Straits. In December, she returned to Norfolk. In January 1940, she moved south again, to Charleston, South Carolina, and in March she headed north for duty on the New England Patrol. World War II Through the prewar Neutrality Patrol period, Roper continued to range the waters off the East and Gulf Coasts. Off Cape Cod on 7 December 1941, it returned to Norfolk for an abbreviated availability at midmonth, and then steamed to NS Argentia, Newfoundland. In early February 1942, it completed a convoy escort run to Londonderry Port, then, in March, returned to the Norfolk area for patrol and escort duty. A month later, on the night of 13/14 April, it made contact with a surfaced U-boat off the coast of North Carolina. The ensuing chase ended with the sinking by artillery fire of , a unit of the 7th U-boat Flotilla. Thus the Roper sank the first German submarine by US naval forces in WWII. According to the after action report, the attack occurred after midnight local time after Roper closed to identify an unknown contact (U-85) and was narrowly missed by a torpedo prior to opening fire. The commanding officer delayed rescue operations until daybreak and after the arrival of air support from a PBY Catalina and an airship due to concern of an attack by a second U-boat. No charges were filed against the crew of Roper and 29 sailors of U-85 were buried with military honors at Hampton National Cemetery. For their actions in sinking U-85, Destroyer Division 54 commander, Commander Stanley C. Norton and the Ropers captain, Lieutenant commander Hamilton W. Howe, were each awarded the Navy Cross. Former commander of German U-boat U-802 and author Helmut Schmoeckel suggested in a 2002 book that the failure of Roper to rescue the U-85 crew