The Douglas B-7 was a 1930s United States bomber aircraft. It was the first US monoplane given the B- 'bomber' designation. The monoplane was more practical and less expensive than the biplane, and the United States Army Air Corps chose to experiment with monoplanes for this reason.' Despite positive evaluation, the Y1B-7 never entered mass production because of its small bomb load and because newer, more capable aircraft, such as the Martin B-10, were under development. Nevertheless, six of the B-7 prototypes, the XO-35 prototype, and the five O-35s all participated in the Airmail Emergency of 1934. All of the O-35s survived and remained in service during the latter 1930s, but four of the B-7s were lost or scrapped in crashes delivering the mail. The surviving two were retired in late 1938 and January 1939.