The Glauco-class submarines were improved versions of the preceding Squalo class. They displaced 1,054 metric tons (1,037 long tons) surfaced and 1,305 metric tons (1,284 long tons) submerged. The submarines were 73 meters (239 ft 6 in) long, had a beam of 7.2 meters (23 ft 7 in) and a draft of 5.12 meters (16 ft 10 in).
For surface running, the boats were powered by two 1,500-brake-horsepower (1,119 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600-horsepower (447 kW) electric motor. They could reach 17 knots (31 km/h; 20 mph) on the surface and 8 knots (15 km/h; 9.2 mph) underwater. On the surface, the Glauco class had a range of 9,760 nautical miles (18,080 km; 11,230 mi) at 8 knots (15 km/h; 9.2 mph); submerged, they had a range of 110 nmi (200 km; 130 mi) at 3 knots (5.6 km/h; 3.5 mph).
The boats were armed with eight internal 53.3 cm (21.0 in) torpedo tubes, four each in the bow and stern. They carried a total of 14 torpedoes. They were also armed with two 100 mm (3.9 in) deck guns, one each fore and aft of the conning tower, for combat on the surface. The light anti-aircraft armament consisted of one or two 13.2-millimeter (0.52 in) machine guns.
Both boats were built by CRDA in its Trieste shipyard. The submarines had initially been ordered in 1931, but were acquired by the Italians when Portugal cancelled the order. Both boats were launched in 1935, and they saw action in the Spanish Civil War and the Second World War.Glauco was badly damaged by the British destroyer HMS Wishart and scuttled by her own crew on 27 June 1941, west of Gibraltar; Otaria was surrendered to the Allies in 1943 and used for training until it was sent to the junkyard in 1948.