The Adua-class submarine was the fourth sub-class of the 600 Series of coastal submarines built for the Regia Marina (Royal Italian Navy) during the 1930s. There were 17 submarines in this class, almost all named after places in Ethiopia which had been an Occupied by Italy since 1936, but only one, Alagi, survived World War II. Three submarines of this class (Gondar, Ascianghi, and Neghelli) were sold to Brazil before the war and replaced with submarines of the same names.
The Adua-class submarines were essentially repeats of the preceding Perla class design. They displaced 680 long tons (690 t) surfaced and 844 long tons (858 t) submerged. The submarines were 60.18 meters (197 ft 5 in) long, had a beam of 6.45 meters (21 ft 2 in) and a draft of 4.7 meters (15 ft 5 in).[1]
For surface running, the boats were powered by two 600-brake-horsepower (447 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 400-horsepower (298 kW) electric motor. They could reach 14 knots (26 km/h; 16 mph) on the surface and 7.5 knots (13.9 km/h; 8.6 mph) underwater. On the surface, the Adua class had a range of 3,180 nautical miles (5,890 km; 3,660 mi) at 10.5 knots (19.4 km/h; 12.1 mph), submerged, they had a range of 74 nmi (137 km; 85 mi) at 4 knots (7.4 km/h; 4.6 mph).[2]
The boats were armed with six internal 53.3 cm (21.0 in) torpedo tubes, four in the bow and two in the stern. One reload torpedo was carried for each tube, for a total of twelve. They were also armed with one 100 mm (3.9 in) deck gun for combat on the surface. The light anti-aircraft armament consisted of one or two pairs of 13.2 mm (0.52 in) machine guns.[1]
The boats, once commissioned, were assigned to complete the squadrons of "600" submarines strengthening the 11th and 14th Squadrons at La Spezia and 43rd at Taranto. After initial training, many of these boats carried out training cruises in the Dodecanese and along the coast of North Africa.
During the Spanish Civil War (1937–1938) five of the submarines already in service made seven special missions on behalf the Franco's regime without much success.
During 1938–39 the boats largely changed their assignment locations: there was at first a single squadron on four submarines at La Spezia four other submarines formed the 23rd Squadron at Naples, and five more were assigned to Leros. In 1939 there was not a single boat of the series at La Spezia, while the squadron at Leros was strengthened. In 1939 four boats from Naples and Taranto bases were sent to Tobruk.
At the outbreak of the World War II, there were four submarines assigned to each of the bases of La Spezia, Cagliari, Messina and Taranto, and one submarine, Macallé was located at the Red Sea base of Massawa.
