The Re.2001 prototype first took to the air in July 1940. Designers Roberto Longhi and Antonio Alessio adapted the structure of the earlier Re.2000 to the new inline engine, remodelling the fuselage but keeping the wing system and tail section. A first delay in finishing the aircraft was caused the authorities objection to the fuel tanks being built into the wings. The had rejected the Re.2000 for the same reason. Several months went by before the designers came up with a new solution and built another prototype. Tests were carried out for some time, and it was June 1941, before the first planes were delivered. Meanwhile the designers had developed a new version in which the radiators were inside the wings. This seemed to be an extremely promising innovation. The first prototype was altered and called the Re.2001 bis. Test flights began in 1941 with Francesco Agello, who had established the world speed record for seaplanes, at the controls. This aircraft flew some 40 mph faster than the standard model, but it never got beyond the prototype stage. Another variant model, developed in 1942, also remained in the prototype stage. Because of the delay in receiving the Daimler Benz engines, the designers found an alternative powerplant in the 840 hp (626 kw) Isotta-Fraschini Delta, a 12-cylinder inverted Vee, air cooled engine. The Re.2001 Delta, as this variant was called, made a series of test flights late in 1942. It crashed in January 1943 and the production order for 100 aircraft was cancelled.

Production of the standard Re.2001 proceeded slowly. About 40 were built in 1941, a little over 100 in 1942, and the rest in the first half of 1943. Alongside the original fighter version there appeared a CB model (fighter bomber) and a CN model (night fighter). The CB had a belly bomb rack that could carry a 220 lbs (100 kg) or a 550 lbs (250 kg) bomb. On rare occasions the plane carried a 1,410 lbs (640 kg) bomb. The CN carried two 20 mm cannon in place the 7.7 mm (0.303 in) machine guns of the standard model. A naval version was also considered. It was to have been carried on board the Italian aircraft carriers Aquilla and Sparviero, then being designed.

The Re.2001's operational career began in December 1941, when it was assigned to three squadrons. The aircraft were used chiefly in the Mediterranean and over Italy as night fighters. After the 1943 armistice there were more Re.2001's with the Allies than with Mussolini's forces in the north. Five aircraft survived the war and remained in service for a few years. While under design it was unofficially called the Falco II, it was known as the Ariete operationally. 

(Reggiane Re.2001CB Ariete "Ram")

Type: Single Seat Fighter

Design: Ingeniere Antonio Alessio and Roberto Longhi of Officine Meccaniche "Reggiane" S.A. (Caproni) based on their previous earlier Re.2000 Falco design

Manufacturer: Officine Meccaniche "Reggiane" S.A. (Caproni) in Reggio Emilia

Powerplant: One 1,175 hp (876 kw) Alfa Romeo RA.1000 RC.41-1a Monsonie (the license built Daimler Benz DB601 A-1) 12-cylinder inline engine.

Performance: Maximum speed 335 mph (540 km/h) with a service ceiling 36,000 ft (10973 m).

Range: 685 miles (1105 km) with internal fuel.

Weight: Empty 4,565 lbs (2070 kg) with a maximum take-off weight of 7,850 lbs (3650 kg).

Dimensions: Span 36 ft 1 in (11.00 m); length 26 ft 10 in (8.20 m); height 10 ft 4 in (3.15 m); wing area 219.59 sq ft (20.40 sq m)

Armament: Two 12.7 mm (0.50 in) Breda-SAFAT machine guns and either two 7.7 mm (0.303 in) Breda-SAFAT machine guns or two 20 mm cannon plus one 1,410 lbs (640 kg) bomb.

Variants: Re.2001 Serie I, Re.2001 Serie II, Re.2001 Serie III, Re.2001 Serie IV (fighter bomber), Re.2001 CN (night fighter). Experimental conversions included a tandem two seat trainer, tank buster, torpedo fighter and one with a Isotta Fraschini Delta IV engine installed.