In 1919, the Boeing B-1 flying boat made its first flight. It accommodated one pilot and two passengers and some mail. Over the course of eight years, it made international airmail flights from Seattle to Victoria, British Columbia. On May 24, 1920, the Boeing Model 8 made its first flight. It was the first airplane to fly over Mount Rainier.
In 1923, Boeing entered competition against Curtiss to develop a pursuit fighter for the U.S. Army Air Service. The Army accepted both designs and Boeing continued to develop its PW-9 fighter into the subsequent radial-engined F2B F3B, and P12/F4B fighters, which made Boeing a leading manufacturer of fighters over the course of the next decade.
In 1925, Boeing built its Model 40 mail airplane for the U.S. government to use on airmail routes. In 1927, an improved version, the Model 40A was built. The Model 40A won the U.S. Post Office‘s contract to deliver mail between San Francisco and Chicago. This model also had a cabin to accommodate two passengers