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were also located more closely together with a cutout in the upper wing to increase visibility. Two different radiators were available, with a larger version for tropical climes. After the prototype was delivered in November 1923, upon the successful completion of tests on 19 November, the Army commissioned Douglas to build four production series aircraft. On 6 April 1924, the four expedition aircraft, named Boston, Chicago, New Orleans and Seattle, departed Sand Point, Washington, near Seattle, Washington.