Before the war, Italian submarines evolved into three different and very distinct designs: the Ansaldo (O.T.O, C.R.D.A.), the Cavallini and the Bernardis. While the first was a civilian design, the other two were the results of design work conducted by engineering officers of the Regia Marina.

The Balilla class was the first of the Alsando group; built in 1925 it was later followed by the Argo in 1931, from which later evolved the Tritone class in 1941. Directly from the Balilla was developed the Calvi class, less than two years after the Argo. The Balilla class was designed by Alsando and built by O.T.O. in La Spezia. The class included four vessels, the Balilla (this was the second unit having this name), the Domenico Millelire, Enrico Toti and Antonio Sciesa. These vessels were designed for oceangoing operations and had a complete double hull. The same design, later improved by O.T.O., was used for the construction of the Calvi class. There were three boats built: Pietro Calvi, Giuseppe Finzi and Enrico Tazzoli.

Typical of this class was an increased range and an improved habitability, thus making the vessels very suitable for long cruises. Unfortunately, these units, slow in maneuvering, were better suited for isolated attacks against slow merchant ships than group actions. Overall, they should be considered successful since the Calvi sunk 29,603 tons, the Finzi 26,222 and the Tazzoli 96,553.