08/31/2015. Remarks by Johan Visschedijk: "The C-4 was so named because it was the third aeroplane design used and the fourth aeroplane owned by Boeing, including a Martin seaplane. It was the second Boeing design (Model 2), even though the firm was still known as Pacific Aero Products at the time it was built, and carried c/n 3 because it was the third aeroplane built.

It was an entirely original design and differed considerably from the B & W both in basic aerodynamic characteristics and general appearance, with small vertical radiators and parallel center section struts. The wings had an unusual degree of stagger and dihedral angle compared to other aircraft of the period for the purpose of providing inherent stability. This was considered by the Boeing engineers as the most desirable characteristic for a training aeroplane. The tail surfaces differed from the B & W in that the horizontal stabilizer was deleted and a vertical fin added. The apparent dark coloring is varnish applied over clear-doped fabric.

The C-4 was dismantled after testing but was rebuilt and flown in August 1918."