SAI Project 403 was introduced in early 1942. Differences from the SAI 207 was a slightly modified fuselage and empennage, larger wing , as well as a new engine Isotta-Fraschini "Delta" RC.21/60 with a 3-bladed constant pitch propeller type Piaggio . The aircraft design was  adapted for mass production. Initially the Italian Air Ministry ordered 2,000  of the SAI serial 207, but in January 1943 plans changed to 3000 SAI 403. Orders were as follows: SAI-Ambrosini - 800, Caproni - 1000, SIAI - 1,200 aircraft.
There were several versions of the fighter projected
"Dardo" A - interceptor armed with two synchronized 12.7 mm machine guns Breda-SAFAT with 350 rounds per gun and take-off mass of 2478 kg.
"Dardo" B - fighter with   two 15-mm machine guns Mauser MG 151/15 in the fuselage and two 20-mm guns MG 151/ 20 in the wing provision for two 150 liter drop tanks.
"Dardo" C - long range  light fighter with two machine guns in the wings with the provision  of two 150 liter drop tanks under the wings, the plane had a projected range of up to 2,230 km.These ambitious plans were not fullfilled. The first prototype of the SAI 403 ( MM.518 ?), was built at the end of 1942 and were flying in January 1943, demonstrated for German representatives  and several Luftwaffe pilot tested it in flight.
Not escaped this fate and SAI-403, who was at the airport in northern Italy. The Germans continued his trial, but in its own test center, where 1944 marks the fighter lost. In all likelihood it could be destroyed in the next raid allies..

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