The Sirena-class submarines were the second in the “600 Series” coastal models of the Regia Marina. They were essentially an improved and enlarged version of the preceding Argonauta capable of 14 knots surfaced for a range of 5,000 nautical miles with six tubes and 12 torpedoes. A dozen boats were built between 1931 and 1934, from OTO, CNT, CRDA, and CQF. They paid a heavy price of WW2 Operations: All but one, Galatea, survived the war. Nine were sunk in action, two were scuttled to avoid capture.

Galatea, Launch Ceremony

Design of the Sirena class

Development

The “600 series” were a new type of standardized coastal submarine for the Italian Royal Navy. They started as an evolution of the 1920s Squalo class. The goal was to provide an homogeneous, standardized class that could be built in numbers by all naval shipyards, and that goupr became the largest in Italian history with fifty-nine submersibles built, and one of the most successful. This group was sub-divided into five classes that did not differ greatly, but improved on each other by successive iterations: The Argonauta, Sirena, Perla, Adua, and Acciaio of WW2. The next were the Flutto class attached to the “900 tonnes” with 48 boats ordered but 7 commissioned as the war progressed.

In capabilities, they were sea-going submarines albeit designated as “coastal”. They were specialized for Mediterranean service and still under interwar naval treaties, with restrictions on the number and individual tonnage: They were limited to a 600-ton surface displacement, albeit France and Italy obtained not having any limitations in their numbers. Germany would later benefit it with the Type VII. Britain also would exploit this catergory with the S-class. The Italian’s 600 tonners really started before the 1930 London conference and reflected somewhat a Franco-Italian naval rivalry which also existed in submarines, as the French started their own 600 tonnes series from 1925.

The Italian 600-tonnes series also met export successes, provided the Argentines with the Santa Fe class. Overall, these performed very well in service, with well thought ergonomics and arrangements, a robust inner hull, excellent seaworthiness, maneuverable, well armed, albeit initially lacking in speed. But for the top brass, speed was not the priority. Next designs tried to constantly improve on the base recipe. The Argonauta initiated the “600” series and based on this first success, the Italian Naval staff ordered a second class, named after the lead board ordered at OTO (Odero-Terni-Orlando) in Muggiano. This next design drafted in 1930 was not a revolution, but an improvement of the Argonauta, sligthly larger.

The Italian Navy decided to order the construction of the Sirena series while the Argonauta series was still under construction. The original design was only marginally revised, with a few minor modifications made: The bow design changed into the “shark” style, which became a trademark of all Bernardis-designed submarines. Construction of the twelve vessels was distributed among four shipyards: Monfalcone obtained six, Sirena, Naiade, Nereide, Anfitrite, Galatea, and Ondina. Tosi in Taranto two: Diamante and Smeraldo. OTO shipyard in Muggiano also two: Ametista and Zaffiro. Quarnaro shipyard in Rijeka also had two, Rubino and Topazio, and these were the only submarines built by them ever, along with Delfinul ordered by Romania.

The large number of submarines in class was a direct result of London Naval Conference of 1930 that granted Italy and France an unlimited number of submarines of this tonnage. This solidified this standard for the future. The naming was an odd choice mixing mythological names like the previous class and diamonds, as the first ran out. For the next series, diamonds were continued, followed by colonial cities mostly in East Africa, and then metals. The ones built by Kvarner Shipyards in Rijeka remained the only submarines ever built by this shipyard for the Regia Marina as an experiment which was never repeated apparently given their lack of experience and final result.

Hull and general design

The Sirena class was an improved and enlarged version of the preceding Argonauta-class submarines. They displaced 691 metric tons (680 long tons) surfaced, so more than allowed by the treaty, as it was their standard tonnage, for 850 metric tons (837 long tons) submerged, versus 660/813 tonnes for the previous Argonauta, so a 30 tonnes rise despite identical dimensions as their precedessors. In dimensions they were slightly shorter at 60.20 meters (197 ft) long overall for a larger beam of 6.45 meters (21 ft) but approximate similar draft of 4.7 meters (15 ft 5 in) as it was estimated the new bow would compensate in buoyancy. Their crew numbered 45 officers and enlisted men, a bit more than the 4 officers and 32 ratings of the previous class. There were however discrepancies in tonnage between yards: 681, 691 or 701 tons surfaced and 842, 850 or 860 tons submerged albeit all had on paper a similar size.

The new “shark bow” was essentially a pointed or “clipper” bow for better seaworthiness, with raised deck, but otherwise the outer hull lines were essentially the same. Just recall there that Bernardis submarines. When decision was taken to start them even before their predecessors could be completed and tested, robbed the possibility to engineers start to really improve on the design based on practical experience, so they reproduced unfortunately some shortcomings of the Argonauta. The main water scoops were located over the ballasts, with a few ones in the bow. It seems the conning tower design was revised as well, albeit details are scarce. It seems the transition between the vertical bulwark of the CT with the deck was the most well refined, and the shape of the aft platform was slighly enlarged. The deck gun was also new, it was the 100mm/47 mm model instead of the old 102mm/35 of the Argonauta, and engines were the improved FIAT 1,350 hp (versus 1,250 hp on the Argonauta) for an also slightly greater range. In around 1941, survivors overhauled among others had their original conning tower cut down and replaced by a “German style” open CT, both to reduce diving time and make them less visible at a distance.

Powerplant

The surface propusion as seen above was improved by the adoption of a new type of FIAT diesel engines, two side by side, for an output of 1,350 (650 hp) but this diverged by yard. Indeed, Diamante, Rubino, Smeraldo, Topazio, the “diamonds” from the Tosi yard in Taranto and CNQ in Fiume had instead two Tosi diesels rated for 1,444 hp (675 hp per engine). Both drove the same four-bladed bronze fixed pitch propellers, for a top speed of 14 knots.

Underwater the standard was two CRDA electric motors for an output of 800 hp (400 hp per engine). But then again, the same four “diamonds” signalled above differed by their kit, as these were Marelli electric motors. In both case the official figure as 1200 and 800 hp respectively in documentation of the time. It seems the Tosi diesels did not improved much on speed. For underwater endurance they had lead-acid battery in two separate rooms amidship under the main deck, consisting of 104 elements.

This provided a top underwater speed of 7.7 knots. Surface range depended on a supply of 80 tons of fuel, same for all boats, providing 2,200 nautical miles at 14 knots (Other sources 2,280 nautical miles at 12 knots) and 5,000 (Other sources 5,590 nautical miles) at eight knots (or 4,480 miles at 8.5 knots). When submerged, this was down to 8 nautical miles at 7.5 knots and 72 (or 84 knm in other sources) at four knots. They could dive, thanks to their stronger pressure hull, to 80 meters or 262 feet, based on a safety coefficient relative to the maximum stress referred to the elasticity limit of the material, of 3.

Sirena was the only one in class to feature the “ML” apparatus, designed in the 1920s already by Naval Engineers Major Pericle Ferretti. This was the Italian version of a snorkel, sucking air from the surface while exhausting engine gases out, ventilating the interior, and enabling submerged (periscope depht) diesel use. This precursor was however only experimentally used and not adopted. The Dutch Navy independently developed a version that was later adopted by the German Navy in wartime and became a cold war staple. The ML was already tested on H3 and nearly adopted for production ordered at CRDA Montfalcone in 1934-35, but Rear Admiral Antonio Legnani decided to suspend production and cancel the order. Without this arbitrary decision, Italy could have deployed an advance asset for its submarine fleet in 1939. The ones later adopted were from German and Dutch origin. One reason for the termination of the program was the apparent poor underwater speed of 1.7 knots, due to the caliber of the pipes and lack of forced draft.

Armament of the Sirena class

Cannone da 100/47 Mod. 1931

Placed on the forward deck, on a raised platform or bandstand well integrated into the hull, acting as wave breaker, to avoid sea spray. This 100 mm/47 (3.9″) Modello 1931 benefited from developments and improvements made on the earlier Modello 1928, as manufactured by OTO. It would later evolved into the Modello 1935 and 1938 retofitted on the next Perla, Adua, Argo, Acciaio and Flutto classes. The boats carried either 144 or 152 rounds.

Specs

Gun Length oa: 194.5 in (4.940 m), 8-10 rpm.
Fixed Ammunition (HE) 30.4 lbs. (13.8 kg) 2,756 fps (840 mps)
Range: 35° 13,800 yards (12,600 m), OTO 1932
Weight 4.6 tons (4.7 mt) -5 /+32 or 35°.
To compare the previous Cannone da 100/43 modello 1927 had the following specs:
170 in (4.300 m) long, 8-10 rom. HE shells: 30.4 lbs. (13.8 kg), muzzle Velocity 2,625 fps (800 mps)
Elevation -5/+35°. Range: 30.4 lbs. (13.8 kg) HE Elevation/35° 12,000 yards (11,000 m).

AA: 2×2 Breda Breda Mod. 31

The anti-aircraft defence counted on two twin Breda M1931 13.2 mm L/76 heavy machine guns, placed aft of the conning tower. Each mount weighed 695 kg, but ensured an elevation of -10° to 90°. They fired 125 g unitary rounds, with a muzzle velocity of 790 m/s, maximum range of 6,000 meters and effective range of 2,000 meters. Their rate of fire was 500 rounds/min, so 2000 rounds when both twin mounts fired in concert, however. They carried a total of 3,000 rounds. It seems before or during the war, this progressed to two twin mounts for extra AA firepower according to many sources.

12x 533 mm (21 inches) torpedoes

The Sirna class submarines repeated the previous class for the stabndardized torpedo armament, six overall including four in the bow, and two in the stern, all reloadable for the pressure hull, and a reserve of 12 torpedoes including the six already in the tubes.
Models available in 1932:
-W 270/533.4 x 7.2 Veloce: 1,700 kg, 7.2 m WH 270 kg, 3,000-4,000 m/50 knots or 12,000 m/30 knots.
-W 270/533.4 x 7.2 “F”: 1,550 kg, 6.500 m, WH 250 kg, speed 3,000 m/43 knots or 10,000 m/28 knots
-W 250/533.4 x 6.5: 1,550 kg, 7.200 m, WH 270 kg, 4,000 m/48 knots or 12,000 m/30 knots.
-Si 270/533.4 x 7.2 “I”: 1,700 kg, 7.2 m, WH 270 kg, speed 3 km/42 kts or 7 km/32 kts, 9,2km/30 knots, 12km/26 kts
-W 250/533.4 x 6.72: 7.2m, WH 270 kg speed 4km/49 kts or 8km/38 kts.
-Si 270/533.4 x 7.2 “M”: 1,7 ton, 7.2 m, WH 270 kg speed 4km/46 kts, 8km/35 kts or 12km/29 kts.
They were also given also a pair of hydrophones.

Profile planned

⚙ specifications as built
Displacement	617-623t surfaced/standard, 830/837 tonnes underwater
Dimensions	60.2 x 6.45 x 4.70 (197 x 21 x 15 ft)
Propulsion	2x diesels Fiat/Tosi 1200 hp, 2 EM CRDA/Marelli 800 hp
Speed	14 kts surfaced, 7.5 knots submerged
Range	5,000 nmi/8 knots surfaced, 72 nmi/4 knots submerged
Armament	100 mm (3.9 in) gun, 2–4× 13.2 mm AA, 6× 533 mm (21 in) TTs (12)
Crew	45

Career of the Sirena

Note: This is a short summary. It will be expanded in a future update.

Ametista (Amethyst) was ordered from Odero-Terni-Orlando (OTO), Muggiano on 16 September 1931, launched on 26 April 1933 and commissioned on 1 April 1934. In the early months of 1940 she was tested as a mothership to carrt SLCs (Maiale human torpedoes) with supports placed on deck, for three Maiale to be placed and secured with cables. The Ametista dived into the roadstead of La Spezia for a test release of the three SLCs from underwater (the drivers mounted on the SLCs released themselves the cables and started the engine). She demonstrated her effectiveness by mining the old scout cruiser Quarto. But the time and complexity of the operation made it clear that this method was not the easiest solution to carry SLCs. Later cylindrical containers were used on the submarines Gondar and the more famous Sciré. She later operated in the Aegean Sea, making 27 combat sorties for 18,000 nautical miles without results. On 9 September 1943, with the armistice of Cassibile, she left Fiume and reached Ancona two days later, then left again at 3:00 PM in the afternoon on 12 September, towing the midget CB. Off the coast of Numana it then decided to scuttle her to prevent capture.

Anfitrite (Amphitrite) was laid down at Cantieri Riuniti dell’Adriatico (CNT) of Monfalcone on 11 July 1931, launched on 5 August 1933 and completed/commissoned on 22 March 1934. She took part clandestinely in the Spanish Civil War, making a few sorties in the Strait of Sicily trying to spot and sink Soviet cargo ships smuggling weaponry to Spain. On 28 or 30 June 1940 while in a mission she was attacked by a Short Sunderland and badly damage by bombs near misses that shook her hull so much that she had to return to port for repairs. On 6 March 1941 in another mission she was spotted by British destroyers and subjected to depth charge attacks. She had to surface later due to heavy damage and HMS Greyhound spotted her, started firing at short range. Anfitritetook a shell in her conning tower, killing all seven officers and watchmen present. The crew scuttled her, as she was now unable to dive, and she was boarded at gunpoint and capured by the British. Amphitrite in all performed 7 missions in wartime, 5 combat patrols and two training or transfers.

Diamante was ordered and laid down to Cantieri navali Tosi (CNT) of Taranto on 11 May 1931, launched on 21 May 1933 and commissioned on 18 November 1933. In 1934 she made a shakedown cruise to the Eastern Mediterranean. In 1937 she clandestinely took part in the Spanish Civil War but had no kills. On 20 June 1940, returning from her combat sortie, she was hit by two torpedoes from the submarine HMS Parthian laying in ambush and and sank in quicklly, about 30 miles north of Tobruk, with all hands, including commander Angelo Parla and 42 men.

Galatea was ordered from Cantieri Riuniti dell’Adriatico (CRDA) from Monfalcone, laid down on 18 July 1931, launched on 5 October 1933 and commissioned on 25 June 1934. She was the only survivor of WW2. Like other subs in class she took part in clandestine Spanish Civil War patrols between 22 August and 5 September 1937, with one missed attack on a merchant ship. On 16 March 1942 she surfaced after spotting a large motor vessel and stopped ger by gunfire warning along prize rules. After boarding her, papers were seized, cargo was examined, the crew was evacuated, and she was sunk with an explosive charge. Immediately afterwards watchmen spotted a rapidly approaching unknown vessel. She launched a torpedo but missed and dived. On 21 November 1942 she made another spotting, and launched four torpedoes against a steamer, off the Algerian coast but missed. The armistice of September 1943 saw her in the right spot, in no danger of catpure, she could join a safe haven and surrendered to the Allies at Bona, being employed in training missions like other Italian subs in co-belligerence, until November 1944. She was then decommissioned on 1 February 1948 after a few more postwar years of training service, and sold for BU. In all she performed 21 sorties, sailing 23,041 miles surfaced and 4,399 submerged.

Naiade was ordered from CRDA Montfalcone and laid down on 9 May 1931, launched on 27 March 1933 and commissioned on 14 November 1933. In the summer of 1937, she clandestinely took part in the Spanish Civil War in the Aegean (no kills). On 12 June 1940, she surfaced and attacked by deck gun a group of pontoons escorted by a gunboat. It seems most her shells were duds and she had to stop the attack, the skipper later complaining about the poor quality of his ammunition. But a few hours later, she spotted and sank with two torpedoes the Norwegian tanker Orkanger (8,029 gross tons). On 14 December 1940, she spotted the British destroyers HMS Hereward and Hyperion and made a run to attack, but was detected before being able to launch torpedoes. She was mercilessly depht charged, and badly damaged, being ultimately forced to surface and scuttled after an epic chase for hours. The entire crew abandoned her and was rescued and captured. There was just on man that died on board, sailor Gaetano Frankfurt, likely the one that setup the charges.

Nereide was ordered from CRDA and laid down on 30 May 1931, launched on 25 May 1933 and commissioned on 18 February 1934. In 1937 she covertly took part in the Spanish Civil War but made no kills. On 12 June 1940 she spotted, torpedoed and damaged a large tanker with a single torpedo hit. In September, she spotted three destroyers west of Zante and Cephalonia, but was never in position to attack them. On 16 July 1941 she spotted and launched two torpedoes against an enemy ship, registered detonations, but the vessel was never sunk. On 12 July 1943, she launched a torpedo array against three destroyers off Taormina but missed. The following day she was detected by ASDIC, by the HMS Ilex and Echo. They started a long chase, dropping all their depht charges and badly damaged her. Forced to surface, she was finished off with gunfire before the crew could evacuate fully and she sank with 21 still trapped inside, 40 miles east of Augusta.

Ondina was ordered at CRDA and laid down on 25 July 1931, launched on 2 December 1933 and commissioned on 19 September 1934. “On 1 July 1940 she attempted to fire on two steamers but was unable to do so due to rough seas[23]. On the evening of 20 June 1941 she sighted the Turkish steamer Refah (3805 tsl) which did not have neutrality markings; the commander Corrado Dal Pozzo therefore thought she was sailing on behalf of the Allies[9] and ordered three torpedoes to be launched; hit, the merchantman sank[23]. On 11 July 1942 Ondina tried to attack the submarine chasers Maid and Walrus but was damaged by their depth charges and forced to surface; hit by their artillery (in the meantime two other units had arrived on the scene) and by aircraft, the submarine scuttled shortly afterwards and the crew was captured[23][24], except for six men who died in the action[25].”

Rubino (Rubis) was ordered from Cantieri navali del Quarnaro (CNQ) in Fiume, laid down on 26 September 1931, launched on 29 March 1933 and commissioned on 21 March 1934. Like the others she performed a single unfructuous sortie in the Spanish Civil War. At 2PM; 29 June 1940, while returning to Taranto after stopping her sorties due to engines issues, Rubino was spotted and attacked by a Short Sunderland. There were near misses and two bomb hits that ruptured her pressure hull; She sank about 150 miles from Cape Santa Maria di Leuca, with 40 of her crew inc. commander t.v. Luigi Trebbi and another officer, but four men were in CT when it happened and survoved, including XO s.t.v. Bracco, all recovered by the Sunderland. That was Rubino’s first wartime sortie and she was also one of the very first sunk Italian sub in WW2.

Sirena was ordered from CRDA of Monfalcone, laid down first in class on 1 May 1931, and launched also first in class on 26 January 1933, commissioned on 2 October the same year. Her motto was “E gurgite dominans” (“from the whirlpools [comes out] dominant”). In 1937 she was part in the clandestine sorties to track down and sunk Soviet cargo ships smuggling arms to Spanish Republicans in the Spanish Civil War. Nothing came out of it. From 20 to 21 June 1940 she spotted and torpedoed a a destroyer off Sollum but missed, the latter followed the trail and starrted a depht charge hunt for hourse, foring her to evasive action, and taking enough damage to return to base. On 29 June while sailing towards Taranto, she was also attacked by a Short Sunderland. She was surfaced and her crew managed to hit her with their Breda 13.2 HMGs (perhaps the two twin mount arrangement). The Sunderland was last seen trailing with smoke and claimed shot down, unconfirmed on the British side. On 4 April 1941 she spotted and launched two torpedoes on a destroyer, claming a hit. On 10 April 1943 she was in La Maddalena when a US bomber air raid sank the heavy cruisers Trieste and Gorizia. Near misses caused 3 dead and 10 wounded while the crew was out of the boat. On 9 September 1943, she was in repair and maintenance at La Spezia and, to depart. She was scuttled by port authorities to avoid capture by the Germans.

Smeraldo (“Emerald”) was ordered from Cantieri navali Tosi (CNT) at Taranto, laid down on 25 May 1931, launched on 23 July 1933 and commissioned on 29 November. She had a single, unsuccessful mission by 1937 in the Spanish Civil War. Her first action was on 11 June 1940 as she was the first Italian submarine to launch a torpedo, which hit home, a merchant ship under escort but was a dud. The night of 7-8 July she was detected and mercilessely hunted down. Her skipper estimated she took some two hundred depth charges. Damage was enormous but she managed to returned to Tobruk to be patched up enough to sail to Augusta for repairs completed only on 2 December. On 18 January 1941 in her third sortie her engines had a breakdown forcing her back. On 16 March she was placed in a good enough position to launch torpedoes at a convoy of seven merchant ships, protected by a cruiser and destroyers, but recounced to fire her torpedoes as the convoy speed and position changed rapidly. Two days later she spotted a light ships, fired and missed while surfaced, but the latter spotted her, reacted by a ramming attack, forcing her to submerge. On 15 September 1941 she joined her designated ambush area off Tunisia, and was never heard of again. Postwar analysis of records showed the British side reporting no kill in that time and area, so the most probable hypothesis was a mine between 16 and 26 September, on the probable route of her return. Cdr. T.V. Bartolomeo La Penna, 4 officers, 40 non-commissioned officers and sailors are on eternal patrol. Smeraldo made 8 sorties over 10,345 miles.

Topazio (Topaze) was ordered from Cantieri navali del Quarnaro (CNQ) in Fiume, laid down on 26 September 1931, launched on 15 May 1933 and commissioned on 26 April 1934. Like the others she was deployed for a single mission clandestinely in the Spanish Civil War, close to Spanish shores. On 12 February 1937, she shelled Valencia until her deck gun exploded probably due to a faulty ammunition. Then came WW2. On 12 July 1940 she rescued six survivors from the destroyer Espero, sunk two weeks earlier, the only survivors of the 36 that drifted since that time. On 11 November 1940 she spotted and launched two torpedoes against a British convoy to Malta, registed two detonations, but gthis never was conformed on the British side. In return, she suffered two hours of depth charge attacks, but survived undamaged. British sources did not even report this attack. On 10 September 1941 under the command of c.c. Emilio Berengan while surfaced she caught and gunned down the British steamer Murefte (691 GRT) finished off with three torpedoes.

On 14 December 1942, Topazio spotted Force K (three cruisers and two destroyers) underway and launched three torpedoes, but missed. On 10 April 1943, she was at La Maddalena dueing the US air Force raid. Topazio was unharmed by near-misses but her crew ashore did suffered one one dead, one missing. At the armistice, Topazio was in the South Tyrrhenian Sea. She decided under orders to head for Bona but disappeared after the evening of 10 September 1943. British sources specified that on 12 September an aircraft (likely a Sunderland) sunk an unknown submarine with bombs,but it was not on course for Bona. Some members of the crew managed to abandon ship but never were rescued leaving no survivors to account on the fate of Topazio. Among the crew in ertenal patrol are CO Pier Vittorio Casarini, 5 other officers and 43 petty officers and sailors. Probably the most active Italian sub in class, she performed 41 sorties for 26,000 miles.

Zaffiro (Zephyr) was ordered from Odero-Terni-Orlando, Muggiano laid down on 16 September 1931, launched 28 June 1933, and commissioned on 4 June 1934. From 24 to 26 December 1941 Zaffiro was used every night off Rosetta to recover SLC “Maiale” operators accomplishing the famous Alexandria mission, but her presence was useless as they all been captured. On 8 June 1942 she left Cagliari for the Baleares but never returned. She was reported later sunk by a PBY Catalina on 9 June, approximately 35 miles south-west of Ibiza (no survivors). Of the 39 includung the CO Carlo Mottura, 4 other officers, 34 NCO and sailors or in other sources as many as 47. Zaffiro performed 22 combat sorties for 15,000 nautical miles. In 2005, Spanish divers located the wreck and attributed it to the Sapphire.

Read More/Src

Books

Bagnasco, Erminio (1977). Submarines of World War Two. NIP
Brescia, Maurizio (2012). Mussolini’s Navy: A Reference Guide to the Regina Marina 1930–45. NIP
Chesneau, Roger, ed. (1980). Conway’s All the World’s Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press.
Frank, Willard C. Jr. (1989). “Question 12/88”. Warship International. XXVI (1): 95–97.
Rohwer, Jürgen (2005). Chronology of the War at Sea 1939–1945: The Naval History of World War Two (3rd Revised ed.) NIP

Links

regiamarina.net
xmasgrupsom.com
regiamarina.net
betasom.it
navypedia.org
uboat.net
regiamarina.net Bernardis type subs
ww2-weapons.com
it.wikipedia.org
en.wikipedia.org
worldnavalships.com

Model kits

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Video: Launch of Sirena (Luce)