The CANT 21 was taken to the air for the first time in 1927 by the new test pilot of the company, the commander Adriano Bacula, then transferred to Vigna di Valle for comparative evaluations with the competitor Savoia-Marchetti S.62.

However, the examining commission considered the S.62 much higher, declaring it the winner of the competition, but the Ministry of Aeronautics gave the CNT the necessary documentation authorizing its production for the foreign market.

The new model, now suitable for three crew members, adopted a different hull, returned to a more classic solution, equipped with a keel and with a considerably lengthened redan, and which housed a second station for the tail machine gun positioned behind the wingspan.

For the engine we chose an Isotta Fraschini Asso 500Ri, the version equipped with a speed reducer, installed in a tractor configuration and combined with a double metal propeller.

We returned to the solution with a drive unit in a pushing configuration, enclosing it in a gondola to reduce the overall aerodynamic drag, and adopting a quadruple helix with variable pitch, with the possibility of adjustment to the ground, coming from another model.