SNCAC NC.600

In October 1934 the French Service Technique de l'Aeronautique (Technical Aeronautical Service) which was dependant of the Air Ministry, issued a requirement for a three-seated fighter. The contenders were Hanriot with its H.220 design, Potez with their 630 design, Breguet with their 690 design and Romano with their R-110 design. The H.220 was a twin-engined monoplane made entirely out of metal. The fuselage was a short, oval-section monocoque which accommodated the crew of three in tandem enclosed cockpits. Shoulder mounted wings were braced by a single short strut on each side and was equipped with full span trailing edge flaps and splits ailerons. It was going to be armed with two fixed forward firing 20mm cannons and two defensive machine-guns in the rear cockpit.
The prototype, which never flew, was fitted at first with two 450hp Renault 12Roi air-cooled V12 engines and was exhibited at the 1936 Paris Air Show.
The prototype was re-engined with two 680hp Gnome-Rhône 14M Radial engines just before flying for the first time in Avord, at the Val-de-Loire region, on 21st September 1937. However, tests showed that it was dangerously unstable and many changes were made therefore to the tail surfaces to try and rectify the problems, but the prototype had to made a forced landing and was badly damaged due to an engine failure on 17th February 1938. That landing wrecked the fuselage of the H.220 and SNCAC, which was a merge of both Hanriot and Farman, following a nationalisation of the aeronautical industry in 1937 took the advantage to carry out a major redesign of the aircraft, rebuilding almost totally the prototype.
The rebuilt and redesigned prototype received the designation of H.220-2, had a new fuselage, built out of two half shells joined by a central keel, with a twin-tail replacing the conventional single-fin tail surfaces of the earlier design. The wings were left unchanged and flew on this new form for the first time on 17th March 1939.
While the redesign process was going on, an order for six aircraft was placed in 1938 for evaluation purposes under the designation of NC.600 as the design was now intended to run for a 1936 specification for a long-range fighter competing against the Potez 670 and the SNCASE SE.100. The modified prototype was exhibited at the 1939 Brussels Air Show, but the real NC.600 was an even further modified aircraft. It featured redesigned wings and tail surfaces and was now a two-seat aircraft. Now it was even more armed with four 20mm forward-firing cannons and the defensive machine guns replaced by a single flexibly mounted cannon.
The prototype of the "definitive" version flew for the first time on 15th May 1940 but it didn't attract the attention of the Armée de l'Air as other types were preferred, like the Potez 671 or the SNCASE SE.100, however, any further work was halted by the French Armistice in June 1940.

Sources:
1. https://en.wikipedia.org/wiki/SNCAC_NC-600
2. Salamander Books - The Complete Book of Fighters