With the additional weight of the pontoon, a number of structural and aerodynamic changes were required, the design of which made use of wind tunnel data developed at the Massachusetts Institute of Technology, meaning the N-9 was the first American naval aircraft to incorporate wind tunnel data directly into its design.

The wingspan was stretched an additional ten feet (three meters), the fuselage was lengthened, the tail surfaces were enlarged, and stabilizing fins were added on top of the upper wing.

Curtiss was awarded an initial contract for 30 aircraft in August 1916, and an additional 14 were ordered by the United States Army, which maintained a small seaplane operation.

It quickly became apparent that the aircraft was underpowered, so Curtiss replaced the engine with a 150 hp (112 kW) Hispano-Suiza, manufactured in the United States under license by Wright-Martin's Simplex division (later Wright Aeronautical).

Fifty others were assembled after the war, from spare components and engines by the U.S. Navy at Naval Air Station Pensacola in Florida.

[2] The United States Army purchased the aircraft for evaluation, but Curtiss repossessed it due to legal issues with the Wright brothers.

In 1917, several N-9s were provided to the Sperry Gyroscope Company for conversion to the Hewitt-Sperry Automatic Airplane configuration, flight testing the new autopilot components intended to be used in pilotless "aerial torpedoes".