As it is well known, during the First World War, the Regia Marina did not have any mine-laying submarines. In the period between the two world wars, when the Italian submarine force was mostly developed, the Regia Marina decided to build mine-laying submarines with performances higher than those of the three existing boats of the X class. More precisely, the intent was to build a boat of medium displacement, good for operations outside the Mediterranean, and with a good balance between launching torpedoes and laying mines.

The project was assigned to Admiral (E) Curio BERNADIS, a talented designer who authored the plans of various excellent submarines. He was the same engineer who, a few years earlier, had designed the mine-laying submarines of the X2 and X3 class using as a model the X1 class. The X1 was an Italian mine-laying submarine rebuilt from the wreck of the Austrian submarine U24 (previously UCF 12 in the Krigsmarine), sunk by one of the mines it was laying in front of Taranto on March 16th, 1916 and later salvaged by the Italian Navy. For this project, Bernardins derived his new design from his previous of the Pisani class, compared to which the new class should have been improved and more innovative with the addition of the mine-laying capability.

Colonel Curio Bernardis, later General, (Note, the Italian Navy uses Army ranking for engineering officers) began the design of a new class of submarines merging the previous design by Laurenti with new, and quite innovative ideas. The goal was to create boats capable of reaching greater depths relying more on the structural integrity of the external part of the resistant hull, rather than the thickness of the internal beans. Bernardis’ design called for a traditional circular hull enclosed at both ends by a semispherical cup. Whiel the ballast tanks were positioned at the end of the resistant hull, inside this there was an additional tank which allowed for high dept operations since it could be emptied both utilizing compressed air and pumps.

The original Bernardis, including the Bragadin and Bragadin, were not very successful, but their evolution gave birth to the Marcello and Marconi classes, some of the most successful products of the Italian submarine shipbuilding effort. The Bragadin Class included only two boats built between 1927 and 1931, and as soon as they underwent testing at sea a serious flaw which has already appeared on the Bragadin Class was immediately discovered: the boat tended to roll quite heavily. To overcome this serious deficiency, the shipyard added some small saddle tanks which, while partially solving the problem, caused the surface speed to drop from 15 to 12 knots, and the submerged one from 9 to 7. To improve stability, some of the equipment was rearranged within the delicate balance allowed by submarine construction.

Eventually, these saddle tanks were integrated in the project and become part of the Bernardis design. Unfortunately, while the problem was still undergoing studying on the Bragadin, the Bragadin were already in advanced state of completion, thus they also had to be retrofitted. Furthermore, on the Bragadin another problem had to be corrected, the boat tendency to dip down by the bow. This problem was resolved by installing a special auto-filling tank which, while the unit was on the surface, would stay empty and give extra buoyancy, while in immersion would fill itself up. Further modifications to the Bardiera gave this class the unique bow which earned the four boats the nickname of “big nose”, or “nasone”.