In 1925, Boeing built its first Model 40 when the U.S. Post Office Department was seeking a design using the World War I-era Liberty engine. When the Chicago-San Francisco airmail contract went for bid, Eddie Hubbard suggested that company engineer Claire Egtvedt replace the water-cooled Liberty with the more efficient Pratt & Whitney air-cooled Wasp engine intended for military fighters.

Company officials convinced Bill Boeing that an improved Model 40 would enable the firm to win the transcontinental contract. That, indeed, happened. The 40A included room for two passengers behind the mail compartment and in front of the open cockpit. Asked how he could operate so efficiently, Bill Boeing said "we're carrying mail over those mountains rather than water and radiators." The 40 could carry twice the payload of its competitors. Later versions of the 40 flew with a Pratt & Whitney Hornet and room for four passengers.

Thanks to the generosity of William E. Boeing Jr. the Museum's Model 40B reproduction was constructed by Century Aviation of Wenatchee, Wash., and was installed in our Great Gallery in October of 2007.