The AUT.18 was a prototype fighter aircraft developed in Italy by Aeronautica Umbra shortly before the outbreak of World War II.

It was designed in 1934 by Felice Trojani, who at that time was collaborating with Umberto Nobile on the Arctic flights of the airships Norge and Italia.

Born from the same Regia Aeronautica requirement that spawned the Caproni-Vizzola F.5, FIAT G.50, Macchi C.200, Meridionali Ro 51 and Reggiane Re 2000 fighters, the A.U.T.18 flew for the first time on 22 April 1939, powered by a 779 kW (1,044 hp) Fiat A.80 R.C.41 radial engine.

Flight trials proved disappointing and lagged behind the other fighters in Progetto R - the modernisation (riammodernamento) of the Regia Aeronautica.

With no production orders forthcoming, despite the prototype being returned to the Umbra factory at Foligno for modifications on 20 February 1940 and a second flight test series from 5 November 1940, no improvement was demonstrated over fighters already in production so the A.U.T.18 was abandoned.