In 1926, the Italian Ministry of Aeronautics announced specifications for a military flying boat capable of long-range reconnaissance flights and bombing attacks against enemy ships and submarines. The company Cantieri Navali Triestini (CNT) participated in the tender for this specification, with engineer Raffaele Conflenti entrusted with its development.
In early 1927, the prototype of the CNT 21 flying boat took to the air. This aircraft, a further development of the CNT 10 and CNT 13 designs, was a two-seater, single-strut biplane, powered by a 510 hp (375 kW) twelve-cylinder V-engine, the Isotta Fraschini Asso 500. Its armament consisted of two 7.7 mm machine guns and light bombs weighing up to 100 kilograms.
Trials and Export Opportunities
The prototype was delivered to the Italian Navy base at Vigna di Valle for comparative trials alongside the Savoia-Marchetti S.62. Although the S.62 was declared the winner of the competition, CNT was permitted to sell the flying boat abroad, opening avenues for international sales.
At the 1928 Paris Air Show, Cantieri Navali Triestini offered the CNT 21 to delegations from Argentina, Portugal, and Turkey. However, only the Argentinians managed to sign a contract, ordering three such flying boats. After the construction of two aircraft, I-AALN and I-AAPW, the Argentine Navy command decided to reduce the order to a single unit. The second aircraft was “placed” with the Uruguayan Navy, which had already ordered two CNT 18bis trainers.
The CNT 21bis and Modernizations
In 1930, the Italian Ministry of Aeronautics announced a new competition to replace the outdated Savoia-Marchetti S.59 flying boats. For this competition, Raffaele Conflenti significantly redesigned the CNT 21. The new aircraft, designated CNT 21bis, became a three-seater, featuring a new, improved fuselage, an Isotta-Fraschini Asso 500Ri geared engine, and a metal propeller. A Marconi R.A.6 radio receiver was also installed.
During the comparative trials conducted by the military at the Vigna di Valle base in 1931, the S.62 was once again declared the winner. The CNT 21bis was further modernized: its engine was enclosed in a streamlined nacelle, and new wings with Handley Page slats were installed. All these changes led to significant performance improvements, but by this time, the competition had been discontinued.
The sole CNT 21bis built was acquired by the Italian Navy but never entered any combat units. It remained at the Vigna di Valle base until April 1940, serving a limited role.
Legacy and Nomenclature
In 1930, after the company’s name change to Cantieri Aeronautici e Navali Triestini (CANT), the designation CNT 21 officially became CANT 21. This renaming marked a new era for the aircraft, even if its operational history remained somewhat limited.
Image and diagram gallery of the CANT 21
