Foca class submarine

Minelaying Submersibles: Foca, Atropo, Zoea (1936-47)

WW2 Italian Submarines

Balilla class (1927) | Ettore Fieramosca (1929) | Archimede class (1933) | Glauco class (1935) | Pietro Micca (1935) | Calvi class (1935) | Foca class (1937) | Marcello class (1938) | Brin class (1939) | Liuzzi class (1939) | Marconi class (1940) | Cagni class (1940) | Romolo class (1943)

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Mameli class (1926) | Pisani class (1928) | Bandiera class (1929) | Squalo class (1930) | Bragadin class (1929) | Settembrini class (1930) | Argonauta class (1931) | Sirena class (1933) | Argo class (1936) | Perla class (1936) | Adua class (1936) | Acciaio class (1941) | Flutto class (1942)

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CM class (1943) | CC class (Laid down) | CA class (1942) | CB class (1942)

The Foca class were three minelaying submarines (sommergibili posamine) of the Regia Marina, sister ships derived from the earlier Pietro Micca but smaller, cheaper, and yet quite capable. They played minor roles during the Second World War, one being lost to unknown causes off British Palestine in 1940 and the other two surviving the war, to be BU in 1947. Their design was peculiar, with a double row of mines running in an longitudinal wells along the hull and chutes at the poop. They also had a defensive gun in the conning tower and were reasonably fast for the time with a sufficient range to roam the Mediterranean and beyond the red sea.

Design of the class

Development

Pietro Micca was a cruiser-submarine in concept, but tailored to lay mines. Launched in 1935 and given her cost, it was quickly established that, despite her capabilities, no follow-up would be ordered, at least in the same package. Plus her minelaying capacity and system were not seemingly optimal. Micca indeed had a “belly well” containing all the 40 mines she carried in two larege holds either side of the keel, in two rows of ten each. This made for a relatively compact “wet room” leaving no cluse on her upper hull to her real nature. A true “secret weapon”. Externally she looked like indeed a regular cruiser sub, well armed with two 120 mm guns. She also had ten torpedoes to complete her patrol’s predation. But at 90 meters (296 feet) long and 1,883 tons submerged she was relatively slow to go under.

Pietro Micca was commissioned on 1 October 1935. She was the largest Regia Marina’s submarine ever built, and if not a bad submarine, her cost prevented any sister-ship, which limited Italy’s abilities to perform potential minelaying operations in wartime. More of the type were needed, Picca was just too large as a design to be practicable. It was thus decided to create already in 1935 a smaller, more compact version, still capable of carrying if possible the same number of mines. Starting with a submerged displacement 200t lighter at 1,600t, standard 1,300t, engineers at Cantieri navali Tosi di Taranto (Micca was built also at Tosi) found an ingenious solution. Keeping the underbelly well which had now smaller dimensions, they found a way to add two outer hull longitudinal wells to carry the remaining mines. After tweaking the design, it was possible to carry 36 mines, 4 mines shy of the objective. However the “hidden feature” that was this minelaying capability was not lost.

Anyway the new design was much more compact, with just one main gun instead of two, in a conning tower instead of the deck, and eight torpedoes instead of ten. The new design was lo longer assimilated to cruiser but mor oceanic submersibles. But as expected, they turned out as hoped, much cheaper than the Micca. In addition they were proven as fast, deep diving, with a long range as Micca, but diving faster and being more agile.

Retrospectively the the «Foca» class were considered best minelayer submarines of the Regia Marina. They belonged to the “Cavallini” hull type, built with a partial double hull, aft longitudinal mine wells, and main belly mine well amidships. The only issue with the “compact design” with a cannon positioned in the rear CT was unusual place and despite its rotating platform, traverse remained poor. This arrangement was later cancelled and the gun moved to a more conventional stern deck location.

About the names:
Pietro Micca was named after a Savoy national hero of 1706, but the new minelayer submersibles would be seemingly named in a rather strange way: Foca (“seal”) was coherent (the British Grampus class were also minelayer subs), atropo (one of zeus’s daughters) and Zoea (A crustacean larva ?).

Hull and general design

The Foca-class submarines displaced 1,326 metric tons (1,305 long tons) surfaced, 1,625 long tons (1,651 t) submerged. The general hull shape wasa bit simpler, with less convoluted shapes than the Micca’s hull, hopefully a bit easier to built. But the ballast bilsters integration was still a work of art. They were still large submarines, but were seven meters shorter at 82.85 meters (271 ft 10 in) long compared to Micca, with a slightly larger beam at 7.17 meters (23 ft 6 in), and similar draft of 5.2 meters (17 ft 1 in), about the same as Micca, to preserve stability. Operational diving depth remained the same at 90 meters (300 ft) but the crew was reduced due to the single gun and in general crampier accomodations at 60 officers and men rather than 72, which made Micca the most labor-intensive RM submarine.
The design of the conning tower was about the same as Micca, with a protected helm’s bridge with windows, and a raised observation platform behind. The two meriscopes, watch and attack, were framed by an imposing fairing. There was also the usual net-guard cable running from the prow to the stern, supported by half masts on deck and a strut between periscopes amidships and the usual leg supported saw. The CT space was much more restricted and she only carried two machine guns for AA defense instead of four.

Powerplant

The Foca class boats had two 1,440 brake-horsepower (bhp) (1,074 kW) diesel engines which drove each of her propeller shafts so that she could run at 15.2 knots (28.2 km/h; 17.5 mph), a bit les than Micca (which had double the output at 3,000 bhp). The latter were the same three-bladed model as the Micca, albeit reduced. When submerged, a pair 625-horsepower (466 kW) electric motors took over. This enabled a top speed of 7.4 knots (13.7 km/h; 8.5 mph) underwater. Micca was capable of 8.5 knots but based on also more than double the power (2x 1600 shp). Which all considered given the end performances at their size, was a quite impressive feat. They were also more efficient, with a range of 7,800 nautical miles (14,400 km; 9,000 mi) at 8 knots (15 km/h; 9.2 mph), compared to 5,000 nm for Micca (but at 9 knots). Submerged they were even more capable, at 120 nmi (220 km; 140 mi) at 7 knots (13 km/h; 8.1 mph) -versus 70 nm at 4 knots for Micca. This was based on 63 tnnes of diesel in normal conditions. Other sources states 8,500 nm at 8 knots, and 106 nm at 4 kts. But this was still much better than Micca.

Armament

The Foca class boats had the same torpedo arrangement as Micca, with six internal 53.3-centimeter (21.0 in) torpedo tubes: Four were located in the bow, and two were located in the stern. The more restrictive internal space imposed a load of eight rather than ten torpedoes. But the main shortcoming was 100-millimeter (4 in) deck gun for surface action mounted at the rear of the conning tower.
On paper, this had advantages. It was believed that the higher position gave it potentially a better chance at hitting targets lower on water, a better view, and better protection from the elements. Similar solutions were shared by British submarines. However this proved an hinderance as many levels, starting with their far more restricted traverse. This gun simply could not shot forward and even was restricted aft to a narrow chase angle. Both the large CT and gun positons were criticized in service and the two survivors were modified in 1941 (see below).

They also had an anti-aircraft armament with two twin 13.2-millimeter (0.52 in) machine gun mounts located in the CT.
The third part, and most interesting design feature was the location of the mines she carried. To manage a total of 36 mines, twenty were stored in a central chamber and the remaining 16 were stored over a roller chain and dropped through two aft chutes. This “belt and suspenders” approach ensured they could lay mines safely in most situations. The longitudinal tubes were 8 mines were stowed were more usable when surfaced at night, but the belly well was a far more “covert” feature.

Cannone da 100/43 Mod. 1927 (1936)

The 100 mm/43 (3.9″) Model 1927 was adopted by the Foca and Brin classes:
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).

Cannone da 100/47 Mod. 1938 (1941)

A slightly improved version of the 100 mm/47 Model 1928 specifically intended for submarines but also used on a few auxiliary vessels. Manufactured by OTO. Slightly shorter than the other 100 mm/47 guns.
In all were developed the 100 mm/47 (3.9″) Models 1931, 1935 and 1938 for Subs, for the Glauco, Marcello, Cappellini, Liuzzi, Marconi, Cagni, Sirena, Perla, Adua, Argo, Acciaio and Flutto classes.
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°.

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 on a rear platform 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.

16x 533 mm torpedoes

Model unknown. When completed it had models powered by wet-heaters:
-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.

P150 and P150/1935 Mines

The mines were manufactured by Pignone, specifically designed to be laid by submarines such as the Foca, Micca and Bragadin classes. Their warhead was either 265 or 331 lbs. (120 or 150 kg) and they had mooring cables 990 feet (300 m) long. On Micca they were located amidship, in a second half-cylindrical outer hull below, in short wells, two rows of ten in a forward chamber and the same aft. They were guided by sloped chutes to pass the axial double keel.

Author’s rendition of Atropo in April 1941

Modifications

In 1941 the two suviving boats were modified. The CT gun was re-sited on the forward deck. In addition it was swapped for a moer modern 100mm/47 OTO 1938 main gun. The large conning tower was re-built to a smaller design. This helped greatly their diving time and reduced noise. By the way, all three were equipped with a similar standard hydrophone set giving some awareness of the surroundings when submerged.

Career of The Foca class

Foca was laid down at Cantieri navali Tosi di Taranto on 15 January 1936. She was launched on 26 June 1937 and completed on 6 November 1937. She had a short operational life. On 13 June 1940, while laying mines off Alexandria by night, surfaced, she was spotted and caught in the projector’s lights of the destroyers Decoy and Voyager in patrol. She made a crash-dive but was hammerred with depth charges for hours but managed to escape. She came out of this unscathed. The following morning minesweepers rushed out to the location.
Shortly after she used her large holds to carry supplies tonthe isolated garrison of Leros, and was back to Apulia on 15 September.
On 8 October 1940 she left for her third and last mission. She was supposed to lay mines near Haifa (British naval base in Palestine) but never reported. Overdue, she was reported missing in action, persumably sunk.
Hypothesis postwar abunded in her fate, but rsearched led to a most probable mine between 12 and 15 October, probably, but most exclusively from a British defensive minefield in the area around Haifa, or a still possible mine (accidental) explosion when laying these, notably due to a contact after turbulences.
Whatever the case, she carried a large crew at the time, 69 men, which well went down with her, including commander Mario Ciliberto), 7 officers and 61 non-commissioned officers and sailors. Her three war missions brought her over 2,063 miles surfaced, 293 submerged. Officially she is accepted “Lost on 13 October 1940 off Haifa”.

Zoea was laid down on 3 February 1936, so not long after Foca, launched on 5 December 1937 and completed on 12 February 1938. Albeit a minelayer she carried mostly transport runs during her wartime carrer, with 21 of such missions. On 18 June 1940 she was the first Italian submarine to do so, leaving for Tobruk with 48 tons of ammunition and relieving the surrounded garrison here. She was back at to Taranto on the 24th. On the 29th she performed her first minelayiong mission, being sent west of Alexandria. Two however exploded accidentally, forcing her minelaying to be interrupted. She had to leave the area fast, and moved south of Crete to complete her mission, but was attacked and damaged by an aircraft, and was forced to return to Taranto with her mine cargo still aboard.

On 10 October, she left Taranto to mine the Haifa area, an important Palestine British naval base. It was probably a creepy mission as her sister Foca disappeared there. But the mission was completed, albeit there are no record of british losses here. In May 1941, she was visited in Bardia by Erwin Rommel, who thanked the crew for a transport run bringing 80 tons of much needed petrol for the Afrika Korps. In the summer of 1941 an error with valves and vents had her rapidly diving and she sank in the port of Taranto. There was almost no personal on board and no victims, and there in shallow waters she was easy to refloat and restored in working order.
In June 1942, while returning from Libya from another transport run with fuel and supplies to Derna (she departed on 24 June), she was attacked by a Bristol Blenheim and like her sister Atraopo, repelled it by AA fire, reporting damage. By September 1943 she took part in the “Zeta Plan”, countering the imminent allied landing at Salerno but was redeployed instead for defensive purposes in the Ionian Sea and learned there about the armistice.

She surrendered to the Allies in Augusta, Sicilia, and on 16 September, moved to Malta to be interned for a short while peinding discussions with the allies. She made her run from Augusta to Malta underwater to avoid both Luftwaffe and allied patrols the entire voyage. On 13 October she left Malta with 14 other submarines back to Italy. Her co-belligerence time was short. Overfue for maintenance, it started in early 1944 but all sorts of shipyard shortages meant this was never completed when the war ended. She was decommissioned postwar and sold for BU in 1947. In her wartime career she conducted 32 missions, inclusing 21 transport runs, the remainder being minelaying and patrols, over 31,192 miles surfaced, 2689 miles submerged.

Atropo was laid down on 10 July 1937 at Tosi, so more than a year and a haf later than Foca and Zoea for early trials return and possible modifications. She was thus launched on 20 November 1938 and completed on 14 February 1939 with the war looming near. Under command of Lieutenant Commander Luigi Gasparrini she underwent a first peacetime mission in the summer (June-July) 1939 to El Ferrol in Portugal, checking conditions for crossing the Strait of Gibraltar. She carried he journalist Paolo Monelli aboard to document this cruise. This clearly announced Mussolini’s contingency plans in case of war.
On 22 June 1940 she left for a first wartime mission at Leros in the Aegean sea. On 26 June, while returning to base, after laying her 36 mines, she spotted a presumably British submarine and attacked, launching two torpedoes off the island of Amorgos, but missed.

On 29 October, she laid 16 mines near Zakynthos, interrupted due to an accidental explosion, strong enough to damage her, so she had to limp back to base.
She became the most successful Italian transport submarine as in this new role, she performed the greatest number of such missions. On May 1941 she made to transport runs to Derna in Libya, and on 17 October a fuel supply mission to Bastia, Corsica.
On 16 November 1941 she suffered four deaths on board, two petty officers, a petty officer and a sailor (what causes ?).
On 19 October 1940 she was attacked while underway at the surface by a lone Bristol Blenheim bomber, but the crew used the four Breda HMGs to repel it and cliamed having damaging it in the process.

At the armistice in September 1943, Atropo sailed to Taranto to waot for further instructions, then left with the submarines Fratelli Bandiera and Jale on 12 September to surrender to the Allies in Malta. She arrived on the afternoon of 13 September, then left on 13 October with a group of 14 Italian submarines back to Italy after an agreement was found and started a much quieter late career in co-belligerence in Bermuda, training allied pilots to ASW.
She cranked up in 1940-43 no less than 30 war missions over 27,884 miles surfaced, 2,703 submerged. Her fate is uncertain after the war. She wa sprobably placed in reserve and BU in 1947.

Read More/Src

Books

Conway’s all the world’s fighting ships 1922-46
Campbell, John (1985). Naval Weapons of World War Two. Annapolis, Maryland: Naval Institute Press.
Fontenoy, Paul E. (2007). Submarines: An Illustrated History of Their Impact. Santa Barbara, California: ABC-CLIO.
Fraccaroli, Aldo (1968). Italian Warships of World War II. Shepperton, UK: Ian Allan.
Kafka, Roger; Pepperburg, Roy L. (1946). Warships of the World. Cornell Maritime Press.
Giorgio Giorgerini, Uomini sul fondo. Storia del sommergibilismo italiano dalle origini a oggi, Segrate, Arnoldo Mondadori Editore, 2002
Alessandro Turrini e Ottorino O. Miozzi, Sommergibili italiani, Roma, Ufficio Storico della Marina Militare, 1999.
Bagnasco, Erminio (1977). Submarines of World War Two. NIP
Chesneau, Roger, ed. (1980). Conway’s All the World’s Fighting Ships 1922–1946. Conway Maritime Press.
Fraccaroli, Aldo (1968). Italian Warships of World War II. Shepperton, UK: Ian Allan.
Rohwer, Jürgen (2005). Chronology of the War at Sea: The Naval History of WW2 (3rd Revised ed.). NIP
Giorgio Giorgerini, Uomini sul fondo. Storia del sommergibilismo italiano dalle origini a oggi, Mondadori 2002,

Links

xmasgrupsom.com
on regiamarina.net/
On trentoincina.it/
on navyhistory.au/
on navypedia.org/
on trentoincina.it/
on it.wikipedia.org/
on xmasgrupsom.com/Sommergibili/foca
trentoincina.it Foca
trentoincina.it/ Atropo
trentoincina.it Zoea
navypedia.org/ calvi.htm
navweaps.com 39/43 m1927
navweaps.com 39/47 m1935
betasom.it successi dei sommergibili italiani iiww

Model Kits

1:700 MARCELLO & FOCA Class Waterline: DELPHIS MODELS