The more powerful Clerget 9B nine-cylinder rotary engine was used by the Nieuport 17bis, which first appeared late in 1916. The N.17bis had stringers fairing out the fuselage sides compared to the flat sides on the 17. The major user was the British Royal Naval Air Service, which ordered 32 from Nieuport, 50 more being licence-built by the Nieuport & General Aircraft Company. Heavier than the preferred Le Rhône, output from the Clerget rotaries quickly fell below their rated power and the performance of the 17bis suffered accordingly. Armament often included a synchronised Vickers gun with the standard over-wing Lewis.