The Douglas B-18 Bolo was designed to meet a United States Army Air Corps requirement given in 1934 to replace the B-10.
The B-18 had many parts based on the DC-2 / DC-3 airliner.
The DB-1 (Douglas Bomber) won against the Martin 146 and Boeing 299. The Boeing 299 crashed and was disqualified. It was to develop into the B-17.