also hampered performance. Triplane At least one 17bis was built as a triplane in the same manner as the Nieuport 17 triplanes, with the wings staggered with the middle wing furthest forward, and the lowest wing furthest aft. Flight testing discovered that it was longitudinally unstable but handled well otherwise, but the concept was not pursued further. Nieuport 23bis The Nieuport 23bis was a later but in many ways a similar development to the 17bis and was the result of the RFC's desperation to get as many aircraft as possible into front line service, but only 17 were produced and all went to the RFC. It combined the flying surfaces including the tail of the 23 with the fuselage of the 24bis, and was fitted with other Nieuport 23 parts, such as an earlier form of cowling. Unlike the 17bis, it retained the Le Rhône normally used by Nieuport scouts. Distinguishing features The 17, 17bis, 23 and 23bis flying surfaces had the front spar positioned further forward than on the later types. Aside from the lack of a plywood leading edge to the wing, the key identifying feature was the rake of the forward cabane struts connecting the top wing to the fuselage. On the 17, 17bis, 21, 23 and 23bis, the cabane struts were angled forward from the fuselage, while on the 24, 24bis, 25 and 27, they were angled aft. Both the 17bis and the 23bis used the square ailerons, rather than the rounded ailerons used on production versions of the later types. Operational history Aside from one example being flown by Charles Nungesser and marked with his personal serial number N1895, the Nieuport 17bis saw little service with the French Aéronautique Militaire. The Royal Naval Air Service (RNAS) was the primary operator of the Nieuport 17bis, with 6 (Naval) Squadron being the only unit wholly equipped with the type. It primarily replaced the obsolete Nieuport 10 and the Nieuport 11 and would in turn be replaced by the Sopwith Camel. The RNAS received 82 examples, of which 32 were from Nieuport (including 1 triplane) and 50 from Nieuport & General Aircraft who built them under licence in the UK. The British-built examples were delivered so slowly that the type had been declared obsolete before most were even delivered and only 4 were known to have been used operationally. As a consequence, most were never removed from their