Franklin D. Roosevelt was the first president to fly in an aircraft while in office. The first aircraft obtained specifically for presidential travel was a Douglas Dolphin amphibian delivered in 1933 which was designated RD-2 by the US Navy and based at the naval base at Anacostia D.C. The Dolphin was modified with luxury upholstery for four passengers and a small separate sleeping compartment.[6] The aircraft remained in service as a presidential transport from 1933 until 1939.[7] There are no reports, however, on whether the president actually flew in the aircraft. During World War II, Roosevelt traveled on the Dixie Clipper, a Pan Am-crewed Boeing 314 flying boat to the 1943 Casablanca Conference in Morocco, a flight that covered 5,500 miles (8,890 km) in three legs.[8] The threat from the German submarines throughout the Battle of the Atlantic made air travel the preferred method of VIP transatlantic transportation.[9][10]