Ettore Fieramosca was designed by the firm Bernardis and was intended to be a cruiser submarine which carried a seaplane in a waterproof hangar and a 203 mm (8 in) gun; such a design was inspired by the similar (although bigger) Surcouf, then under construction in France. Several prototype seaplanes were designed but not deployed and the hangar was removed in 1931. The deck gun was initially a 120 mm (5 in) 27-calibreOTOmodel of 1924, but this was later replaced by a 120 mm 45-calibre OTO model of 1931.[1]
However Ettore Fieramosca proved to be rather over-dimensioned for her armament, slower than intended—the intended speed of 20 knots (37 km/h; 23 mph) while surfaced was never achieved—with poor maneuverability, both surfaced and underwater, and rather poor endurance. Due to her huge cost and these shortcomings, plans to build more boats to the same designs were shelved.[2]
Plagued with incidents and mechanical trouble for her entire career, she was deployed on only a few operational patrols in 1940, but did not achieve any successes against enemy targets.
She suffered a battery explosion late in 1940 and was decommissioned in April 1941; eventually she was stricken and scrapped.[2]