Westervelt, who had been reassigned to the East Coast in December 1915, consulted heavily on the design.

Wong Tsu, an MIT graduate who was hired by Boeing in May 1916, also contributed to the design, specifically lending his expertise in the analysis of wind tunnel data.

The Model C-1F had a single main pontoon and small auxiliary floats under each wing and was powered by a Curtiss OX-5 engine.

The success of the Model C led to Boeing's first military contract in April 1917 and prompted both its reincorporation as the Boeing Airplane Company and relocation from Lake Union, Washington to a former shipyard on the Duwamish River, also in Washington.

On March 3, 1919, Boeing and Eddie Hubbard flew the C-700 on the first international mail delivery, carrying 60 letters from Vancouver, British Columbia to Seattle, Washington.