First flown on 10 July 1938 the FN.315 was an improved version of the FN.305.

The FN.315 was a low-wing cantilever monoplane of mixed construction.

It had tailskid landing gear, with the main gear retracting inwards, and room for two crew in tandem in an enclosed cockpit.

It was powered by a nose-mounted inline piston engine and various engines were evaluated during flight trials, originally with a 205 hp (153 kW) Alfa-Romeo 115 and also a 200 hp (149 kW) Argus As 10E and a 230 hp (172 kW) Hirth HM.508.

A further 25 Alfa-Romeo powered aircraft were built for the Italian Air Force and were used as intermediate trainers.