Italian submarine Diaspro

Italian submarine Diaspro was a Perla-class submarine constructed for the Royal Italian Navy (Regia Marina) during the 1930s. The vessel’s name was inspired by the gemstone Jasper.

Design and description

The Perla class represented a near replication of the earlier Sirena class series, incorporating primarily enhancements rather than fundamental redesigns. Key upgrades included an enlarged false tower on the conning tower, more advanced engine models, and the addition of a radiogoniometer operable from within the submarine. Further improvements involved new air conditioning systems and increased fuel capacity, which collectively contributed to a modest rise in displacement and extended operational range compared to their predecessors. The designed full load displacement typically reached 695 metric tons (684 long tons) when surfaced and 855 metric tons (841 long tons) submerged, though slight variations existed depending on the specific vessel and shipyard. These submarines measured approximately 197 feet 6 inches (60.20 m) in length, with a beam of 21 feet (6.4 m) and a draft ranging from 15 feet (4.6 m) to 15 feet 5 inches (4.70 m).

For propulsion on the surface, two diesel engines powered individual propeller shafts, delivering a combined output between 675–750 hp (503–559 kW). While submerged, each propeller was driven by an electric motor rated at 400-horsepower (298 kW). The submarines could achieve speeds of up to 14 knots (26 km/h; 16 mph) surfaced and 7.5 knots (13.9 km/h; 8.6 mph) underwater. Their surfaced endurance allowed for a range of approximately 5,200 nautical miles (9,600 km; 6,000 mi) at a cruising speed of 8 knots (15 km/h; 9.2 mph), whereas submerged range was limited to around 74 nmi (137 km; 85 mi) at 4 knots (7.4 km/h; 4.6 mph).

Armament included six internal torpedo tubes measuring 53.3 cm (21.0 in), with four located in the bow and two in the stern. Each tube had one reload available, totaling twelve torpedoes carried onboard. Surface combat capability was provided by a single 100 millimetres (3.9 in) deck gun. Defensive anti-aircraft weaponry consisted of one or two pairs of 13.2 millimetres (0.52 in) machine guns.

Construction and career

The submarine Diaspro was constructed by CRDA at their Trieste shipyard, with its keel laid on 29 September 1935. It was subsequently launched on 5 July 1936 and finalized by 22 August 1936.

Following its commissioning, Diaspro was assigned to the 35th Squadron (III Submarine Group) stationed at Messina. After a short period dedicated to training, the submarine undertook an extended endurance patrol in the Mediterranean. During the Spanish Civil War, under Captain Giuseppe Mellina's command, Diaspro executed two covert assignments. The first mission began when she departed from Trapani on August 5, 1937, tasked with patrolling north of Cape Bon. While monitoring the Strait of Sicily near the African coast, she launched 25 attack attempts. On August 13, 1937, she fired torpedoes at two vessels, one likely being the Template:GRT French cargo ship SS Paramé, though both attacks were unsuccessful. Diaspro returned to Cagliari on August 15, 1937.

The second mission commenced from Naples on August 25, targeting patrols off Cape Oropesa. On September 1, near Benicarló, Diaspro encountered a tanker en route to Alicante. Unable to intercept it submerged, she engaged on the surface by launching two torpedoes, which were detected and evaded by the tanker’s crew. The tanker then attempted to ram the submarine. Subsequently, Diaspro fired two additional torpedoes that struck amidships, sinking the vessel. The submarine's captain identified the target as a 6987 GRT Republican tanker bound for Alicante under the likely false name SS Woodford, with a Romanian crew. In reality, the tanker was operated by a British company and was transporting petroleum from Constanta to Valencia. Diaspro returned to Naples on September 5, 1937.

When Italy entered World War II, Diaspro was part of the 72nd Squadron (VII Submarine group) based at Cagliari. Its initial mission in the Tyrrhenian Sea resulted in no significant encounters.

In July 1940, she conducted patrols northwest of Asinara and near the island of La Galite. The following month saw her operating off Cap Bougaroûn.

On September 1, during British Operation "Hats," Diaspro patrolled between Cape Spartivento and La Galite. She approached within ten miles of British Force H but was forced to submerge due to detection and repeated aerial attacks from aircraft launched by the carrier Ark Royal.

On November 9, 1940, she departed from Cagliari alongside four other submarines to intercept a British convoy as part of Operation "Coat," but no enemy vessels were sighted.

By November 14, Diaspro operated with submarines Alagi and Aradam as a screening force against British ships involved in Operation "White." Positioned approximately 315 miles from La Galite, she detected only a minor enemy vessel but was unable to launch an attack.

On January 21, 1941, Diaspro and Corallo patrolled off northern Tunisia.

Throughout February, May, and June of 1941, she undertook three missions east of La Galite Island, about twenty miles north of Cape Blanc, and south of Sardinia respectively; none yielded successful engagements.

On July 21, under Captain Antonio Dotta's command, Diaspro departed Cagliari for an operational area approximately 55 miles off Cape Bougaroun. Arriving the next day, she commenced surface patrols with periodic submergence for hydrophone checks. At around 22:58 after seven hours and covering 45 miles, she closed in on a British naval group within 1,000-1,300 meters and launched four bow torpedoes at cruisers at 23:07. Two minutes later she fired two stern torpedoes targeting a battleship and an aircraft carrier. The destroyer HMAS Nestor detected the initial torpedoes and alerted other ships; their formation maneuvered starboard to evade them. The stern torpedoes passed beneath Nestor due to depth settings aimed at larger vessels. Nestor retaliated with depth charges that inflicted only minor damage on Diaspro.

Between late July and early August 1941, Diaspro patrolled southwest of Sardinia alongside three other submarines aiming to intercept a British convoy during Operation "Style," but no contacts were made; subsequently she was redeployed near La Galite.

In September of that year, initially stationed off La Galite Island, on September 28 she moved east of the Balearic Islands near Menorca as part of a screen against British Operation Halberd naval forces; however, no British ships traversed those waters. Ordered southward thereafter, on September 29 at approximately 6:17 she spotted enemy vessels about forty miles northwest of Philippeville at coordinates 37°32′N 6°45′E. She launched two torpedoes targeting destroyer HMS Gurkha, which successfully detected their wakes and evaded them.

On October 20, while patrolling off Cape Fer, Diaspro observed Force K's ships but could not engage due to distance constraints.

From April through September 10, 1942, she was assigned to the Submarine School at Pula, completing thirty-two training sorties before returning to active service based in Cagliari.

On November 8, near Cape Bougaroun while approaching her patrol zone, Diaspro collided underwater with Italian submarine Alagi. The latter sustained severe damage whereas Diaspro incurred only minor harm allowing continuation of her mission. Four days later in Bougie harbor vicinity she launched four torpedoes from approximately one thousand meters at a transport ship which evaded them all; a fifth torpedo exploded without confirmed hits on any target. Command passed to Alberto Donato on November 12.

December saw her patrolling off Bona (Algeria), entering its harbor on December 14 but achieving no successful attacks.

In May 1943 she operated west of Sardinia.

During July that year while patrolling southwest of Sant'Antioco near Cape Fer on July 13th morning sightings included a large merchant escorted by two corvettes. She fired four torpedoes hearing two detonations but apparently inflicted no damage. One corvette counterattacked with depth charges causing no harm to Diaspro. She returned to Cagliari the following day.

On August 18 off Stromboli she unsuccessfully fired two torpedoes at two British destroyers. The next evening en route to Naples she intercepted two destroyers and launched four electric torpedoes at them around 23:23. About an hour later one destroyer appeared disabled; however lacking further torpedoes she could not renew her assault.

As part of the Zeta Plan on September 7, 1943, Diaspro joined ten other submarines deployed in the Tyrrhenian Sea—initially in the Gulf of Salerno then off Gaeta—to counter expected Anglo-American landings in southern Italy. On September 8 she remained deployed when ordered to cease hostilities following Italy’s Armistice announcement. For three days thereafter she stayed at sea uncertain whether to surrender at Bona (Annaba). After consulting commanders of two other submarines Captain Donato chose compliance but first had engine repairs carried out in Cagliari.

By March 1944 after repairs were completed she relocated to Taranto where her role shifted primarily towards training Italian naval personnel.

Under Emilio Botta’s command on July 17 that year, Diaspro embarked on a mission transporting espionage agents who were disembarked in two groups—first in Zante and then Kefalonia—returning safely to Brindisi by July 22.

From April until August 1945, Diaspro served as an anti-submarine warfare training platform for Allied naval forces while based in Malta.

Following the war's conclusion, Diaspro was disarmed at Taranto and officially struck from records on February 1, 1948 before being dismantled.

Ships sunk by Diaspro

Date	Ship	Flag	Tonnage	Ship Type	Cargo
September 1, 1937	SS Woodford		6,987 GRT	Tanker	Fuel Oil
Total:			6,987 GRT

References

• Bagnasco, Erminio (1977). World War Two Submarines. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.
• Chesneau, Roger, ed. (1980). Conway's Complete Guide to Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press. ISBN 0-85177-146-7.
• Rohwer, Jürgen (2005). Naval War Chronology 1939–1945: The History of World War Two at Sea (Third Revised ed.). Annapolis, Maryland: Naval Institute Press. ISBN 1-59114-119-2.
• Bargoni, Franco (1992). Italian Naval Involvement in the Spanish Civil War (1936–1939). Mondadori. ISBN 88-98485-07-7.
• Frank, Willard C. Jr. (1989). "Inquiry 12/88". Warship International. XXVI (1): 95–97. ISSN 0043-0374.
• Giorgerini, Giorgio (2002). Manned Below: The History of Italian Submarines from Their Origins to Present Day (Second ed.). Mondadori. ISBN 88-04-50537-0.
• Pollina, Paolo (1963). Italian Submarines 1895–1962. Rome, Italy: SMM.