[1] Flight testing of the prototype revealed it to be able to outfight several significant combat aircraft of the time, including even the more modern Macchi C 200 and the German Messerschmitt Bf 109E fighters.

[4][5] Refinement of the Re 2000's aerodynamic characteristics greatly benefitted from a series of wind tunnel tests held at Caproni's facility in Taliedo, Milan.

[6][7] According to Cattaneo, early flights had quickly demonstrated the type's favourable flying attitude, including good speed and high manoeuvrability.

Only minor modifications were required after the successful completion of the initial factory flight test programme; these including changes to the exhaust, the lengthening of the carburetor air intake, and the replacement of the round windshield with a framed counterpart.

[6] Following the completion of armament trials at Furbara, Santa Marinella, in August 1939, the prototype was delivered to the Experimental Establishment of the Regia Aeronautica to commence its formal evaluation.

[2] In mock dogfights, it could successfully fight not only the slower Fiat CR 42 biplane,[8] but even the more modern Macchi C 200 and the German Messerschmitt Bf 109E fighters.

[6] Amongst its findings, it judged the placing of the integral fuel tanks within the wings to be highly vulnerable and prone to leaks, as well as posing some difficulty to manufacture.

[10] The Re.2000GA (Grande Autonomia) version featured additional 340-liter fuel tanks, which was primarily achieved by sealing off the cells of the outer wing structure, to function as a modern long range reconnaissance aircraft for the Regia Marina (Italian Navy).

[10] This version was intended to have been used to reach Eastern Africa; during 1941, the Italian government was keen to acquire an aircraft which would be able to fly directly from Italy to Ethiopia.

By adopting the Re.2000GA, Italy would be able send reinforcements to the units of the Regia Aeronautica far easier, unlike a batch of 51 C.R.42s that had to be disassembled and air-transported by the large Savoia-Marchetti SM.82s instead.

[6] However, according to Cattaneo, the Re.2000 was afflicted by a major handicap in the form of the unavailability of reliable in-line engines of sufficient power; as such, the RE.2000 was able to represent only a limited advance over the Macchi C.200.

[4] The Re.2000 was powered by a single Piaggio P.XI RC 40 radial engine, which was capable of generating a maximum of 986 hp (735 kW) of thrust; this drove a Piaggio-built three-blade constant speed variable-pitch propeller.

[11] The aircraft was furnished with an elliptical wing, the internal structure of which comprised a multi-cell configuration using a total of five spars, stress-skin covering, and integral fuel tanks within the center section.

[6] The wing made use of a modified N.38 airfoil section and was outfitted with Frise-type ailerons complete with static and aerodynamic balance, along with a split-continuous flap.

[6] The armament comprised a pair of 12.7 mm Breda-SAFAT machine guns, housing 300 rounds each, installed in the upper fuselage; in addition, provisions were made for the fitting of bomblet-dispensers (spezzoniera).

[6] This armament, while typical amongst Italian-built aircraft at the time, was relatively light in comparison to foreign-built rivals then being constructed; additional weapons, such as the installation of a pair of wing-mounted guns, was studied but never applied.

[1][9] Following the decision of the Regia Aeronautica to reject the Re.2000 and cancel its pre-production order,[1] the Italian government authorised Reggiane to promote the type for sales on the global market to international customers, effectively offering the programme a reprieve.

Enthusiastic, the company decided to proceed with the production of the original batch of 188 fighters that had been cancelled as a private venture so that immediate delivery could be offered to foreign customers.

[2] In December 1939, a British commission, led by Lord Hardwick and Air Ministry representatives, arrived in Italy for the purpose of purchasing various pieces of military equipment; aside from items such as marine engines, armaments and light reconnaissance bombers, the delegation sought to procure of around 300 Re.2000s.

Although the Reggiane had a long range, it was disliked and even feared by ground crew and pilots, for its difficult maintenance and unpredictable engine reliability and handling.

[19] The work to make suitable the Re.2000 Cat., nicknamed Ochetta (little goose) took considerable time and only at the beginning of 1943 were they used aboard the Littorio class, but not more than one for every ship (although capable of holding three aircraft).

[3] There was the usual Italian armament (two 0.50 caliber Breda machine-guns with 300 rounds each), and some provisions for external loads (tanks or bombs), apparently never utilized.

During the Roma's sinking (9 September 1943) only one was launched, as they were a single mission aircraft (forced to reach a land airfield); therefore, Do 217s attacked facing only anti-aircraft guns.

Moreover, Adolf Hitler held a bad opinion of the Hungarian aviators, expressing this view in early 1942 when Hungary issued another request for German-built fighters.

[26][28] It also had a newer, more powerful (1085 hp) Hungarian engine – the WM K-14B, a redesigned cowling, a larger Hungarian-made Weiss Manfréd propeller, and more changes further differentiating it from the Re.2000.

[30] Flying alongside the Fiat CR.32s of 1/3 Fighter Company, the Héja I pilots claimed eight kills for one loss during three months of combat against the Soviet Air Force.

Between 16 and 19 January, with the Red Army rapidly approaching Ilovskoye airfield, and with no time to heat the engines' frozen oil, mechanics were forced to blow up the last unserviceable Héja Is.

[40] Production of Héja IIs in Hungary continued until August 1944: 98 were completed in 1943 and 72 in 1944, although the aircraft was regarded as no longer suitable for combat against the latest Soviet fighters.

The Swedish purchases of various types of Italian warplanes in 1939–41 were made as an emergency measure resulting from the outbreak of the war, as no other nations were willing to supply aircraft to this small neutral country whose domestic production did not become sufficient until 1943.

However, the Re.2000's mechanical reliability was unable to meet Swedish Air Force requirements; reportedly, the aircraft normally had to spend a great deal of time in maintenance.