The source dates the photo in 1927, but the N number hints at 1928 at the earliest and Washington - New York Airline ads we found are from 1929. The lower title seems to read 'Leased from United States Air Transport', and that company supposedly existed between 1929 and 1930. Hoover Field in Arlington, where the Pentagon now stands, was a very small and notoriously dangerous airport, surrounded by a smoking landfill, radio masts and even a roller coaster. Photo from: Arlington Public Library