Perla-class submarine

The Perla-class submarines were the third sub-class of the 600 Series of coastal submarines built for the Royal Italian Navy (Regia Marina) during the 1930s and named after gemstones. Of the ten boats built of this class, only three survived World War II.

Design and description
The Perla-class submarines were essentially repeats of the preceding Sirena-class submarine. The modifications that were made compared to the boats of the previous series were mostly of upgrade nature. Among them were enlargement of the false tower at the top, more modern engines, installation of a radiogoniometer that could be controlled from inside the ship. Improvements and the installation of new air conditioning equipment meant a slight increase in displacement, and increase in the fuel stowage also increased the autonomy of these boats compared to the previous series. Their designed full load displacement was 695 t surfaced and 855 t submerged, but varied somewhat depending on the boat and the builder. The submarines were 197 ft long, had a beam of 21 ft and a draft of 15 ft to 15 ft.

For surface running, the boats were powered by two diesel engines, each driving one propeller shaft with overall power of 675 - 750 hp. When submerged each propeller was driven by a 400 hp electric motor. They could reach 14 kn on the surface and 7.5 kn underwater. On the surface, the Perla class had a range of 5200 nmi at 8 kn, submerged, they had a range of 74 nmi at 4 kn.

The boats were armed with six internal 53.3 cm 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 deck gun for combat on the surface. The light anti-aircraft armament consisted of one or two pairs of 13.2 mm machine guns.

Service
The boats, once commissioned, were assigned to complete the squadrons of "600" submarines from La Spezia (12th and 13th Squadrons) and Messina (34th and 35th Squadrons) and began their training and exercises in metropolitan waters, and underwent endurance training predominantly in the Dodecanese and, to a lesser extent, along the coast of North Africa. These endurance exercises took place in 1936 and 1937, soon after the initial training was finished.

ITALIAN SUBMARINE Iride and ITALIAN SUBMARINE Onice were "lent" to the Nationalist side during the Spanish Civil War, under the names of Gonzales Lopez and Aguilar Tablada respectively, in the framework of Italy's aid to Franco's regime. They retained their Italian crews but had a Spanish liaison officer on board. They were returned to the Italian Navy at the end of the conflict.

In 1938 ITALIAN SUBMARINE Perla and ITALIAN SUBMARINE Gemma were sent to the Red Sea base of Massawa and returned the following year replaced by ITALIAN SUBMARINE Onice, ITALIAN SUBMARINE Berillo and ITALIAN SUBMARINE Iride who in turn returned to Italy before the outbreak of World War II. Between 1938 and 1940 ITALIAN SUBMARINE Ambra and ITALIAN SUBMARINE Malachite were for long periods of time deployed outside of Italy, mainly in Tobruk.

At the outbreak of hostilities, four boats were located at La Spezia, three in Cagliari, two in Augusta and one, ITALIAN SUBMARINE Perla, in Massawa.

After a disastrous start to the World War II when Italy lost ten submarines in the first twenty days, and the Regia Marina and Regia Aeronautica did not fare much better, Italian command decided to speed up implementation of experimental SLC technology. In July 1940 ITALIAN SUBMARINE Iride was modified to carry 4 "Maiale" manned torpedoes in watertight containers on the deck of the submarines. ITALIAN SUBMARINE Iride was sunk while conducting tests, before she could be employed against British naval units. ITALIAN SUBMARINE Ambra underwent conversion to SLC in March 1942 with three SLC units being fitted onto her deck. With a weight of 2.8 tons, these SLC cylinders were able to withstand depths up to 90 meters, about three times more than those installed on ITALIAN SUBMARINE Iride. In December 1942, ITALIAN SUBMARINE Ambra managed to penetrate Algiers harbor, and sank or seriously damaged several merchant ships with a total GRT over 20,000.

In common with other Italian submarines the survivors were fitted with smaller conning towers in 1942–43.

Overall, the Perla class submarines proved to be quite successful. They showed good maneuverability, their hull was well designed and strongly built to withstand depth pressure and explosions that exceeded their test values.