The Ambrosini SAI.403 Dardo ("Dart") was a light fighter aircraft built in Italy during World War II.
SAI.403 Dardo was a considerably refined version of the SAI.207, designed during the delays in that type's development. The improvements induced the Ministero dell' Aeronautica in 1943 to cancel its order for 2,000 of the SAI.207 so as to order 3,000 of the SAI.403 instead (800 from Ambrosini, 1,000 from Caproni, and 1,200 from Savoia-Marchetti). Apart from the fighter's superlative performance, its all-wood construction was attractive at a time when Italy was facing a shortage of strategic materials. However, by the time of the Armistice, the first of these was yet to leave the factory.
The single prototype (MM.518) was seized by the Germans and evaluated by the Luftwaffe at Vergiate. Japanese pilots then stationed in Germany were also given a chance to fly the aircraft, with the result that it was ordered into production by both Heinkel and Mitsubishi. None of these flew before the end of the war.