The F.4 had been redesigned to take the German DB 601Aa engine, finally flying with this in late 1940. Results were excellent, but Fabrizi decided not to pursue this, developing it instead with the more powerful DB 605A of 1475 hp, which was to be built in Italy as the Fiat RA1050 RC58 Tifone. With this engine the F.6 flew in 1942, and subsequently an all metal F.6M was built, passing through various development stages. Basic armament was four 12.7 mm (0.54n) Breda SAFAT machine guns. Several developments were projected, most having the X-form Isotta Fraschini Zeta engine, but the Armistice halted further work in September 1943.Engine: Daimler-Benz DB 605A.

The F.4 and F.5 were designed in parallel with the 890-hp (664-kW) Isotta-Fraschini Asso 121 inline and 870-hp (649-kW) Fiat A.74 radial engines respectively. They had traditional mixed construction, with welded steel tube fuselage with light ¬alloy skin and wooden wings. Landing gear and flaps were hydraulic, and ailerons were arranged to droop with extension of the flaps. Tailplanes had variable incidence for trim¬ming.
The F.5 was the first to fly, in early in 1939, and was evaluated against the Fiat G.50 and Macchi MC.200 for a production order, but the only contract placed was for 14 pre-production fighters. These had a modified cockpit canopy, greater fuel capacity, larger vertical tail surfaces, and a non-retracting tailwheel. The F.5s were used from mid-1940 for the night defense of Rome in the first months of the war, and then employed as interceptors until lack of serviceability forced their retirement. Armament was two 12.7 mm (0.5 in) Breda SAFAT guns. Fabrizi had numerous schemes for developments of the F.5, but none was built.

Caproni Vizzola F.5
Type: single-seat fighter.
Engine: one 870-hp (649-kW) Fiat A.74 RC 38 radial piston
Maximum speed: 317 mph (510 km/h) at 9,845 ft (3,000 m)
Climb to 21,325 ft (6,500 m): 6 minutes 30 seconds
Service ceiling: 31,170 ft (9,500 m)
Range: 478 miles (770 km).
Empty weight: 4,078 lb (1,850 kg)
Maximum take-off weight: 5,181 lb (2,350 kg).
Wing span 37 ft 1 in (11.30 m)
Length 25 ft 11 in (7.90 m)
Height 9 ft 10 in (3.00 m)
Wing area 189.45 sq ft (17.60 sq.m)
Armament: two fixed 0.5-in (12.7-mm) machine guns.

The F.4 and F.5 were designed in parallel with the 890-hp (664-kW) Isotta-Fraschini Asso 121 inline and 870-hp (649-kW) Fiat A.74 radial engines respectively. It was then decided to fit the more powerful Daimler-Benz DB 601A in the F.4, and the delay thus caused meant that the F.5 was the first to fly, an event that took place early in 1939.
The F.4 had traditional mixed construction, with welded steel tube fuselage with light alloy skin and wooden wings. Landing gear and flaps were hydraulic, and ailerons were arranged to droop with extension of the flaps. Tailplanes had variable incidence for trimming.
The F.4 finally flew in late 1940 with the DB 601A, and it was then decided to concentrate on an improved F.6 with the DB 605A.

The Caproni Ca 355 Tuffo was flown for the first time in January 1941. Powered by an 850 hp Issotta-Fraschini Delta IV engine and possessing an undercarriage based on that of the Curtiss P-40, The Tuffo carried its 1100 lb bomb on an articulated rack. Flight testing was successful but no production orders were placed and only the sole prototype was built.