Tham khảo Witteman-Lewis XNBL-1

Ghi chú
    1. ↑ Report on Official Performance Test of Barling Bomber, NLB-1, P-303, Light Load Configuration, 14 April, 1926.
    2. ↑ "Factsheets: Witteman-Lewis XNBL-1 Barling Bomber." National Museum of the United States Air Force, ngày 25 tháng 6 năm 2009. Truy cập: ngày 26 tháng 8 năm 2011.
    3. 1 2 3 Swanborough and Bowers 1963, p. 504.
    Tài liệu
    • Allen, Francis J. "Flying Battleship: Walter H. Barling and the Wittemann-Lewis NBL-1". Air Enthusiast, No. 98, March/April 2002, pp. 66–73.
    • Arnold, Henry H. Global Mission (Military Classics Series). New York: Tab Books, 1989, First edition 1949. ISBN 978-0-8306-4004-1.
    • "The Barling Bomber: An American Six-engined Giant." Flight, ngày 13 tháng 2 năm 1923, pp. 749–751.
    • Cornelisse, Diana G. Home Field Advantage. Wright-Patterson Air Force Base, Ohio: U.S. Air Force Publications, 2004. ISBN 0-16-068065-4.
    • Cornelisse, Diana G. Splendid Vision, Unswerving Purpose: Developing Air Power for the United States Air Force During the First Century of Powered Flight. Wright-Patterson Air Force Base, Ohio: U.S. Air Force Publications, 2002. ISBN 0-16-067599-5.
    • Moy, Timothy. War Machines: Transforming Technologies in the U.S. Military, 1920-1940 (Texas A & M University Military History Series). College Station, Texas: Texas A&M University Press, 2001. ISBN 978-1-58544-104-4.
    • Report on Official Performance Test of Barling Bomber, NLB-1, P-303, Light Load Configuration. McCook Field, Dayton, Ohio: Air Service Engineering Division, War Department, Flight Test Unit, Flight Research Branch, 14 April, 1926.
    • Swanborough, Gordon and Peter M. Bowers. United States Military Aircraft since 1909. London: Putnam, 1963.
    • Tilford, Earl H., Jr. "The Barling Bomber." Aerospace Historian, June 1979, pp. 91–97.
    • Winchester, Jim. The World's Worst Aircraft: From Pioneering Failures to Multimillion Dollar Disasters. London: Amber Books Ltd., 2005. ISBN 1-904687-34-2.