found: Work cat: Hagedorn, D. The Douglas B-18 and B-23, 2014.
found: Virtual Aircraft Museum website, 30 Dec. 2014:Aircraft directory: U.S.A.: Douglas aircraft (Douglas B-18 Bolo, 1935)
found: National Museum of the USAF Fact sheets website, 30 Dec. 2014(Douglas B-18)
found: Wikipedia, 30 Dec. 2014(The Douglas B-18 Bolo medium bomber served with the United States Army Air Corps and the Royal Canadian Air Force, as the Douglas Digby, during the late 1930s and early 1940s; a B-18 was one of the first American aircraft to sink a German U-Boat, the U-654 on 22 August 1942 in the Caribbean)
