The U.S. Navy Sikorsky XPBS-1 patrol bomber prototype (BuNo 9995) while being evaluated by the National Advisory Committee for Aeronautics, 25 July 1938. The Sikorsky XPBS-1 was a large four-engined flying boat ordered by the Navy in 1935. Although never ordered into production, the NACA evaluated the craft in 1938. Many aircraft were flown at Langley to give an appraisal from the highly experiences staff. These appraisals often meant that the aircraft was with the NACA only briefly.