Submarines of the Second World War

In the interwar period France built a formidable submarine force which was classified into three groups: long-range submarines for high-sea patrols, short-range submarines for defense patrols and minelayer submarines. Regarding Great Britain, the first submarines built in that same time were designed for carrying out operations in the Pacific Ocean, so they were large long-range vessels. At the beginning of the decade of 1930 the Royal Navy was enhanced with three submarines of the Thames class. However, since their speed did not allow them to navigate alongside the rest of the war fleet, no more vessels of this class were built, and the effort was concentrated in minelayer submarines and mid-size patrol submarines.

During the First World War the German developed the "U-Cruiser" or long-range submarine armed with heavy cannons and specifically designed for the destruction of merchant ships which navigated the ocean in isolation. After the war the Japanese and the American built several vessels of this kind. Until 1939 the two largest submarines ever built were the experimental cruiser submarines built by Great Britain and France (the X-1, the only vessel of the Royal Navy which was built during the interwar period and scrapped before 1939, and the Surcouf, respectively). This latter was armed with the heaviest cannons ever installed in a submarine - besides that of the British M class - and equipped with a Besson seaplane and a motor boat which was later removed. The two 203-millimeter cannons had a complete fire control system and they could have eliminated an escort of armed merchant ships, corvettes and other lightly armed ships from a distance at which a response from those could have not been possible. The 400-millimeter torpedoes were relatively light short-range weapons designed for being used against merchant ships, albeit this clever idea did not yield results as good as expected.

However, given her high cost and large crew, the Surcouf seemed a somewhat doubtful investment. At the time when this submarine was built it was not foreseeable that France had to fight against Great Britain, the only country against which this submarine could have been useful. At the beginning of the Second World War she accumulated one disgrace after another. Her chance came when she was sent to the Pacific Ocean, where she could have inflicted losses to the Japanese merchant fleet. However, during the travel she was accidentally hit and sunk by a merchant ship. She had already demonstrated to be an unlucky vessel when, after having fled from Brest during the German invasion of 1940, she arrived to Great Britain only to be seized, following an unfortunate skirmish, by her hosts. Later, in service with the Free France, she was hit by one of the first anti-submarine rockets ever fired, most unfortunately by an Allied aircraft.


The Surcouf was the largest submarine afloat in 1939 and the last armed with large-caliber cannons.



During the interwar period France built a formidable submarine force. With the exception of the Surcouf, they were classified into three types: long-range submarines for high-sea patrols, short-range submarines for defense patrols and minelayer submarines. The submarines of the Requin class were the first oceanic submarines built during the interwar period. They were quite well armed in relation to their size, with four torpedo tubes in the bow and two in the stern, as well as two pairs of removable tubes installed in the superstructure, afore and abaft the conning tower. In the interwar period removable torpedo launchers were installed in the largest part of the French submarines, for being used against merchant ships. Unfortunately, the submarines of the Requin class had a relatively short operational range, so they were soon superseded by the twenty-nine units of the Redoutable class, which had a displacement of 1,600 tonnes in surface and an operational range of 10,000 nautical miles at 10 knots in surface. Between 1937 and 1940 five improved submarines of the Roland Morillot class were laid down, but they were destroyed before having been completed because of the German invasion.

The submarines of the Requin class were extensively modernized between 1935 and 1937. The Morse sank near Sfax (Tunisia) after hitting a mine and the Narval hit another mine in the same place six months later. The Souffleur was sunk by the British submarine HMS Parthian. The Caïman was scuttled in Toulon to prevent her capture by the German. The Requin, Dauphin, Phoque and Espadon were captured in Bizerte (Tunisia) and incorporated to the Royal Italian Navy. The Phoque was later sunk by Allied aircraft near Sicily. The Marsouin was captured by the Free France.


Submarine of the Requin class as they appeared before the 1935-1937 modernization.

The minelayer submarines of the Saphir class carried thirty-two mines in sixteen vertical tubes placed amidships in the ballast tanks. This arrangement, known as the Normand-Fenaux system, was based in the British system used in the minelayer submarines of the E class from the First World War. The submarines of the Saphir class had two torpedo tubes in the bow and a removable triple launcher, which comprised one 500-millimeter torpedo tube flanked by two 400-millimeter torpedo tubes, installed astern in the superstructure. The 400-millimeter torpedo was a short-range weapon specifically intended for sinking merchant ships, but it did not yield great results in this regard.

With the exception of the time period comprised between November 1936 and May 1939, the submarines of the Saphir class were based in the Mediterranean Sea. Before the fall of France all of these units carried out minelaying missions. The Diamant was scuttled in Toulon to prevent her capture by the German. The Saphir, Turquoise and Nautilus were captured by the Italian in Bizerte (Tunisia). The Perle and Rubis joined the Free France. The former was mistakenly sunk by an Allied aircraft and the latter survived the war after having carried out twenty-two minelaying missions.


The Rubis is depicted here as she was on completion of her refit in May 1943. Note the British pendant number P.15 on her conning tower and the Oerlikon anti-aircraft cannon which had been added at the after end. The outline of the minelaying wells can be seen on the saddle ballast tanks in the plan view.



Like the cruisers of the County class, the first British submarines of the interwar period were designed for operations in the Pacific Ocean, so they were large long-range vessels. The cruiser submarine X-1 had a displacement of 2,634 tonnes in surface, an armament comprising two 132-millimeter cannons and six 533-millimeter torpedo tubes and an operational range of 12,400 nautical miles in surface. Her experimental Diesel engines were extraordinarily reliable. However, this submarine was scrapped in 1936, after having spent only ten years in service.

The nineteen submarines of the O, P and R classes, built between 1925 and 1931, were much more conventional units. They had a displacement in surface ranging from 1,332 to 1,499 tonnes and an armament consisting of one 102-millimeter cannon and eight 533-millimeter torpedo tubes. The prototype HMS Oberon had an operational range of 16,800 nautical miles in surface, albeit it was reduced in the subsequent submarines. With the exception of the fuel losses in the external tanks, they were vessels of excellent quality for operations in the Pacific Ocean. Unfortunately, because of the scarcity of this kind of vessels they had to be used in the Mediterranean Sea. They were too large and poorly maneuverable for those closed waters, so eleven units out of a total of fifteen which operated there were lost.

At the beginning of the 1930s three submarines of the Thames class were built. The latest two could navigate at a speed of 22.5 knots in surface, but this was not enough for staying at the same speed than the rest of the war fleet, so no more units of this class were built. During the same decade eight minelayer submarines of the excellent Porpoise class were launched. Another three which had been already planned were cancelled, following the development of a mine which could be launched from a torpedo tube, which rendered minelayer submarines completely obsolete.

In the meantime the mid-size patrol submarines of the S class were being built. The British Admiralty was trying to achieve an international limit of 610 tonnes in the displacement of submarines in surface, and the S class was designed with this condition in mind. They were built for being used in the North Sea or in the Mediterranean Sea. They were extremely maneuverable and capable of a very fast immersion. To contend with the improved air-to-surface tactics a heavy torpedo armament was installed to allow the launching of large salvos which assured results in long-range attacks. The first group had one 76-millimeter cannon installed in a folding mounting in front of the conning tower, whereas the second group had the cannon installed in a fixed deck mounting. These submarines were put into production once again during the Second World War and they were extraordinarily efficacious units in action. Some of these submarines were of partially welded construction whereas others were of integrally welded construction. Some of them were later modernized by removing their cannons and modifying their conning towers, to accommodate them to the hydrodynamical profile generally adopted during the early postwar period.

The new long-range patrol submarines of the T class were designed for replacing the vessels of the O, P and R classes. Their size was restricted to keep their displacement under the tonnage allowed by the London Naval Treaty, but as those of the S class they were fitted with a powerful torpedo armament. All the fuel was carried in internal tanks and small improvements were made as the Second World War progressed. The subsequent submarines were of either partially or integrally welded construction. Those specifically intended for operating in the Pacific Ocean had additional fuel tanks. Some of these submarines were modernized after the war, but eight of those built through integral welding were elongated and completely rebuilt, so their speed in immersion was almost doubled. Near the end of the Second World War, the A class was developed from the T class to serve in the Pacific Ocean. These submarines, which had a displacement of 1,138 tonnes in surface and were of integrally welded construction, had a greater operational range and achieved a greater speed in surface.

The U class was initially one of unarmed training submarines, intended for replacing the H class from the First World War. These small and very maneuverable submarines could be built very quickly and, after having been fitted with torpedo tubes, they were extremely efficacious in the rough waters of the North Sea and in the Mediterranean Sea. These submarines were superseded by those of the V class, which was an improvement of the U class and whose vessels were of partially welded construction. At the end of the Second World War the largest part of these submarines were reassigned to training missions. The S, T and U classes were not spectacular designs nor were they endowed with the most modern technological advancements of that time, but their units were very well armed, reliable and capable of a quick immersion. Their operational capabilities were comparable to those of foreign contemporary submarines.


The HMS Upholder of the U class is depicted here in the "Mediterranean Blue" color adopted by all of the boats of the 10th Submarine Flotilla which operated from Lazaretto, Malta, during the three critical years spanning from the last half of 1940 to the end of 1943. In glassy calm conditions, the shape of a patrol submarine could be sighted by enemy reconnaissance aircraft at depths of up to 30 meters.



The 895 vessels of the Type VII, Type IXB and Type XIV classes endured the burden of the German submarine offensive during the Second World War. After the initial trials with the submarines built in Finland between 1930 and 1933, and after the possession of submarines was unilaterally legalized by Great Britain in the Anglo-German Naval Treaty of 1935, Germany took the leading position with its submarine construction program. It had claimed equality with the countries of the Commonwealth while stating that it would not build more than 45 percent of the quantity agreed, unless the situation rendered it necessary. Sir Samuel Hoare, who later became Secretary of Foreign Affairs, stated that "the Naval High Staff, believing that we had the submarine threat under control, raised no objection to the concession". This acquiescence brought as consequence the almost complete defeat of Great Britain, whose submarine construction program had begun in 1935.

The submarines of the Type IA, Type IIA, Type IIB, Type IIC and Type IID classes were no more than training vessels in comparison with those of the Type VIIA class and its subsequent classes, the first of which was launched in 1936, following a project which had begun a few years before that date. They were excellent submarines endowed with a speed of 17 knots in surface and a great maneuverability due to their twin rudders. They were ideal for surface attacks and totally comparable to any of their contemporary counterparts, with an operational range in immersion of up to eighteen hours at four knots. Their weak point was the storage of compressed-air bottles in a container in which they could be broken during an attack. On the other hand, the discomfort of the central corridor in every living space was notorious.

The Type VIIA, Type VIIB and Type VIIC were in general very similar classes, but the latter had a more resistant pressure hull. The Type VIID was ten meters longer to accommodate five minelaying tubes with three mines on each of them. The Type VIIF had the same length than the Type VIID to carry twenty-five torpedo reloads for supplying other vessels during navigation. The Type IXA, Type IXB, Type IXC and Type IXC/40 classes were longer versions of the Type VII class, but the Type IXD1 and Type IXD2 were eleven meters longer and the latter had two additional Diesel engines. This new arrangement granted an operational range of 20,580 nautical miles at 12 knots. Several of the Type IXD submarines were used for carrying first-necessity goods imported from Japan, and others were used as supply vessels, a role which caused the loss of many units.


Submarine U-565 of the Type VIIC class. Capable of a speed of 17 knots in surface and endowed with a great maneuverability, the vessels of the Type VII class were very suitable for combat operations.


On her second patrol off Freetown, the U-107 sank more tonnage than any other German submarine during the Second World War. This Type IXB submarine is shown here as she appeared after having received an anti-fouling treatment on return from patrol in 1941. Note the 105-millimeter cannon in front of the conning tower as well as the 37-millimeter and 20-millimeter anti-aircraft cannons abaft and atop it.

The ten submarines of the Type XIV class were built as supply submarines. They were familiarly known as "milky cows" and none of them survived the war. They carried 437 tonnes of fuel, as well as four torpedo reloads, and contributed to a great extent to the success of operations as the German submarines inflicted growing losses in the poorly defended eastern coast of United States, in the first months of 1942. The "friendly cow" was surely a very pleasant vision in the "Happy Days" of the 22nd and 23rd April 1942, when fourteen submarines were refuelled in an area of 800 kilometers around the Bermuda Islands, which allowed the German to sink eighteen ships between Cape Sable and Key West. However, these supply submarines were particularly vulnerable and, despite their better prestations when navigating in immersion, nine units were sunk by aerial attacks and only one by surface ships.


The supply submarines of the Type XIV class were characterized by a deep hull, a slightly raised bow and a conning tower located rather rearward.


To compensate the growing losses of submarines which took place from the middle of 1943, the German technicians focused on the design of vessels which were true submarines rather than mere submersibles. The submarines propelled by Walter hydrogen-peroxide turbines were built in certain quantity but too unreliable for service. These turbines were based on the employment of very concentrated hydrogen peroxide and a catalyst to obtain the driving energy. Submarines fitted with this propulsion system reached a speed of 25 knots in immersion when they were tested in 1945. An alternative system was adopted in the oceanic submarines of the Type XXI class and the coastal submarines of the Type XXIII class. The external hull was given a more hydrodynamical shape, which granted better prestations in immersion than in surface, and the power of the batteries of Diesel-electric submarines was widely increased. However, albeit both designs were intended for an extensive production and a large number of units was built, only few of these new submarines carried out operational patrols. Their true meaning came after the end of the war, when they formed the base of the foreign Diesel-electric developments. The Whiskey and Narval classes (Soviet and French, respectively) were basically improvements over the Type XXI class which paved the way for newer designs of own creation.
This comprehensive depiction of a submarine of the Type XXI class shows her most important characteristics: the double-hull construction with a very hydrodynamical external hull, the twin 30-millimeter cannon turrets in the conning tower, the large amount of batteries for propelling the submarine when this one is submerged and the great number of torpedo reloads in the fore section.



The Shch class, also known as Shchuka class, was the first class of submarines completely designed in the Soviet Union. The first vessels of the 3rd Series were designed in the late 1920s and then progressively developed. Their operational range was enough for patrolling the sea during twenty days. The vessels of the 5th Series, which had two variants, had their hull and conning tower reinforced, as well as an additional cannon. Their speed in surface was increased, for the first units of the 3rd Series reached a top speed of only 11 knots during their trials. The vessels of the 10th Series had their hull further reinforced and their speed further increased, and those of the 10th-Bis Series increased their prestations significantly. The surviving units from the previous groups were adscribed to the 10th-Bis Series.

The Soviet named their first submarines of own design with fish names, including them in a numeral classification as well. The units operating in the Pacific Ocean belonged to the 100th series, those operating in the Black Sea belonged to the 200th series, those operating in the Baltic Sea belonged to the 300th series and those serving in the Arctic Ocean belonged to the 400th series. The service life of these submarines during the Second World War was not spectacular, as was the case with the whole Soviet Navy as well. While only a few German vessels were lost because of Soviet submarine attacks, the Soviet suffered a large proportion of disasters. The poor performance of the Shch class was probably due to a greater extent to the inappropriate equipment and training of the crew rather than to inherent design defects in the submarines. The Shch-305 was sunk in 1942 by the Finnish submarine Vetehinen and the Shch-214 was torpedoed by an Italian patrol torpedo boat of the MAS series.




The Japanese based their submarine program largely on large vessels of the cruiser submarine type, copied from German designs, which were suitable for operating throughout the whole area of the Pacific Ocean in an effective way. Such vessels were characterized by a notorious displacement, an excellent artillery equipment and an extraordinary operational range. However, this conception of submarine warfare did not dissuade the Imperial Japanese Navy from building in 1934 more than 2,000 midget submarines with a displacement close to 19 tonnes and capacity for one or two crewmen. Regarding the United States Navy we can highlight the excellent quality of its submarine project, which determined the success of the submarine warfare operations carried out during the Second World War. The American submarines sank nine out of ten large Japanese vessels throughout the war in the Pacific Ocean.

The I-400 and I-201 classes represent both ends of the Japanese submarine project. After the end of the First World War the Japanese obtained the blueprints of the German cruiser submarines, from which they developed successive classes of large submarines capable of operating effectively in the whole area of the Pacific Ocean. Among the submarines belonging to fifteen classes launched in 1931, several were prepared for carrying aircraft which allowed to effectuate long-range reconnaissance. These units were built with gradually larger sizes until arriving to those of the I-13 class ordered in 1943, which had a displacement of 4,883 tonnes in immersion and an operational range of 17,700 nautical miles. However, they were surpassed by the submarines of the I-400 class.

The Japanese developed three types of cruiser submarines: Type A, headquarters units which had a floatplane and additional communications equipment to coordinate the groups of the other two types; Type B, standard cruiser submarines similar to those of the Type A apart from lacking the headquarters facilities; and Type C, which were better armed than the other two types but devoid of aviation facilities for being able to carry "Kaiten" crewed torpedoes. The submarines of the I-400 class were designed for carrying out all of the aforementioned missions, besides carrying bombs and torpedoes for attacking the Panama Canal. To reduce the draught of these large submarines their hull was built with an eight-shaped cross section. Nonetheless, the submarines of the I-400 class did not enter action, because this kind of large submarines had already demonstrated how easy was to destroy them once they had been localized, due to their poor maneuverability. Besides, the American often achieved localizations with their anti-submarine vessels, thanks to their ability of deciphering the Japanese naval codes. However, the Japanese soon found an answer, albeit they did not develop it as quickly as they should have.


Regarding the standpoint of naval construction, the submarines of the I-15 class solved the problems posed by the transportation of aircraft onboard submarines. Like other excessively ambitious projects, the submarines of the I-400 class, large and vulnerable, with a broadly defined role, were disappointing in almost every aspect.


In 1937, twenty years later than the British R class and several years before the German Type XXI class, the Japanese tested the No. 71, an extremely hydrodynamical submarine which had better prestations in immersion than in surface. The Type ST (I-201 class) and Type STS (Ha-201 class) submarines, which were comparable in many aspects to the German submarines of the Type XXI and Type XXIII classes, were developed from that submarine. Unfortunately, the obsession of the Japanese for building large submarines caused that those submarines were not put into production until 1944-1945. Both types were extensively tested by the American after the war. The Type ST submarines were the first ones which entered action and their prestations were, in many aspects, comparable or even superior to those of the German designs.


The very modern silhouette of the No. 71 shows that the Japanese technicians knew how to achieve high underwater speeds, albeit the bow shape was far from being perfect. The No. 71 was armed with three 450-millimeter torpedoes. The submarines of the Ha-201 class were small, fast and highly maneuverable, like the German counterparts of the Type XXIII class. But, like these, they appeared too late for being used in the war despite the pace of their production.


The Japanese built a large amount of midget submarines from 1934, and equipped cruiser submarines and aircraft carriers to transport them. The Type A had two torpedo tubes and a crew of two men. The Type B and Type C had a Diesel generator for recharging their batteries and a crew of three men. The Type D "Koryu" had a Diesel engine and a crew of five men. The first three types were designed for carrying out offensive operations, whereas in 1945 a considerable number of Koryu submarines was built for defensive operations in Philippines, Okinawa and Japan. Some of them had explosive warheads instead of torpedoes, for being used as suicide weapons. A modified version of the Type A was built for this purpose as well, albeit both this one and the Koryu were too large and complex for being built in large amounts. Because of this the Japanese modified the Type 93 610-millimeter torpedo for carrying a piloting man, and called it "Kaiten" Type 1. The Type 2 was tested with an unfortunate hydrogen peroxide engine and the Type 3 was a merely experimental model. To achieve an effective weapon, the Type 2 and Type 4 (the last version produced) were fitted with a conventional torpedo engine. The crewed torpedoes of the Kaiten class were the product of despair and it seems that they did not attain a remarkable success regardless of having been produced in a significant amount (over 2,000 units).


In 1919 United States and Japan obtained the plans of the German cruiser submarines, which they used for the development of long-range submarines which were suitable for carrying out operations in the Pacific Ocean. The Cachalot class introduced the technique of welding the hulls and the subsequent Porpoise class introduced the fast and reliable Diesel injection engines which the United States Navy had proposed and advocated, and which meant a considerable advantage in relation to the designs of other countries. These submarines had a Diesel-electric propulsion system. During the Second World War their conning towers were modified and two 20-millimeter anti-aircraft cannons were added. Some vessels had as well two external torpedo tubes installed in the bow. The Winton, Fairbanks-Morse and Hooven-Owens-Rentschler engines were later developed and the United States Navy adopted them as the standard for its subsequent submarines. These extraordinarily reliable engines were the foundation of the success of the American submarines in the Pacific Ocean during the Second World War.

The submarines of the Porpoise class were smaller than the first American submarines from the interwar period, but they had to sacrifice very little regarding their armament, capabilities and operational range in comparison with the earlier large submarines. The relatively small size of their engines contributed to this. The submarines of the Porpoise class had slightly different silhouettes according to their classification group, albeit all of the units were modified in a very similar way during the Second World War, with the installation of light anti-aircraft cannons in the conning tower. The surviving vessels of the Porpoise class were not operational after the war, but they were assigned to the reserve.


Submarine belonging to the 1st Group of the Porpoise class with the modifications effectuated during the war.


During the Second World War the American submarines, which usually operated at considerable distances from their bases, sank nine out of ten large Japanese ships. The interception of the Japanese secret codes had an extraordinary importance, but the quality of the American submarine program was decisive for the success of the operations. The bulk of the contender submarines comprised 73 units of the Gato class, 132 units of the Balao class and 31 units of the Tench class, which was a development from the former classes. The main difference between the submarines of the Gato and Balao classes lied in the reinforced hull of the latter, which allowed them to reach a depth of 120 meters. In turn, the Gato class was a progressive development from the Porpoise class. With the adoption of a policy of gradual improvements, the American built submarines which, regardless of not being of an overall excellent quality, were extraordinarily reliable regarding some aspects and offered a great operational range and an excellent habitability. Besides, they could carry a large amount of torpedo reloads.

After having perfected four types of high-speed Diesel engines, the American had tested a composite transmission system (with direct and Diesel-electric drive) in the Salmon and Sargo classes and a Diesel-electric transmission system in the Porpoise, Mackerel, Tambor and Gar classes. This arrangement was chosen for the Gato class as well. The high speed attained when navigating in surface proved to be invaluable for getting good positions for launching the torpedoes. These submarines had six torpedo tubes in the bow and another four in the stern. They carried 24 torpedoes, which seemed enough, but their cannon armament was enhanced throughout the war. The production of these submarines was facilitated by their integral welding construction, which was carried out in four shipyards. One of these was located in Manitowoc, a town in the shores of Lake Michigan, where the vessels had to be side launched and from where they had to navigate almost 1,000 kilometers along the Mississippi River until reaching the sea. These submarines were very reliable but the Mark 14 torpedo used between 1941 and 1943 was not and it often failed to explode.

The largest part of the 54 submarines of the Gato class which survived the war were converted to the normalized GUPPY 1 class, leaving them without their cannons and with a more hydrodynamical conning tower. Six units were transferred to foreign countries and seven were refitted as submarine hunters, with more powerful batteries which granted a greater underwater speed. The USS Tunny (SS-282) was turned into a launching platform for the Regulus I surface-to-surface missile and later, in 1964, into a transport submarine. This fortunate class and its derivatives showcase the success of the American policies regarding the development of hull designs and extraordinarily reliable engines during a long time span. However, the workflow was reduced because there was not a real necessity of smaller and more maneuverable short-range submarines, so these were produced in small amounts only.


The USS Barb (SS-220) is depicted in section as she appeared in 1944. Note that an Oerlikon 20-millimeter anti-aircraft cannon on the forward conning tower's platform has been omitted.

Categories: Submarines - World War Two - 20th Century - [General] - [General]

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Article submitted: 2025-06-08

Article updated: 2025-07-09