These standardized submarine types shared many common features. Functionally, they were submersibles rather than true submarines; their designs were optimized for operation on the surface, and they had only limited capabilities while submerged. Underwater, they relied on electric motors powered by large storage batteries for propulsion; on the surface, they used diesel engines for propulsion and to recharge the batteries. The submarines incorporated substantial numbers of torpedo tubes and reload torpedoes, and they also mounted guns for use against surface or aerial targets. Their operational range was a function of the capacity of their bunkers for diesel fuel; their radius of action while submerged was limited by battery cell capacity. Maximum speed while submerged usually was not much more than half their surface speed, and maintaining high submerged speeds was impossible for any length of time without totally draining the batteries and forcing the submarine to the surface. Consequently, most navies during the conflict primarily operated their submarines as stealthy surface vessels that could submerge for evasion or escape before or after an attack.
British submarine development was influenced by the cruiser and fleet submarine concepts. The main thrust of early evolution between the wars centered on the overseas patrol type, which displaced 1,475 tons on the surface and had a range of 10,900 miles at 8 knots, a submerged endurance of 36 hours at 2 knots, and a diving depth of 500 feet. Armament included a battery of 8 torpedo tubes with 14 torpedoes and a 4-inch deck gun. A group of similar-sized minelaying submarines also was built, as was a small series of very fast large submarines for work with the fleet, but both of these developments proved very expensive and of limited operational usefulness.
In the early 1930s, a fresh start was made with the Swordfish-class, which was designed for offensive patrols in narrow waters. These boats displaced 640 tons standard. They had a cruising range of 3,800 miles at 9 knots on the surface and 36 hours at 3 knots submerged, and they could dive to 300 feet. Armament was 6 torpedo tubes with 12 torpedoes and a 3-inch gun. A larger overseas patrol type, the Triton-class, appeared in 1937. These displaced 1,090 tons standard; they had a cruising range of 4,500 miles at 11 knots on the surface and 55 hours at 3 knots submerged, and they could dive to 300 feet. Armament was 10 torpedo tubes with 16 torpedoes and a 4-inch gun. Britain concentrated its production of submarines during the war on these two types, producing a total of 62 of the S type and 53 of the T type.
Just before the war, the Royal Navy developed a small submarine for training not only crews and new commanding officers but also antisubmarine vessels. When war came, the design was quickly adapted for operational use, and the submarine proved particularly useful in confined waters such as the North Sea and Mediterranean. The U class displaced between 540 and 646 tons on the surface, with a range of 3,600 miles at 10 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 200 feet. Armament included a battery of 6 torpedo tubes with 10 torpedoes and a 3-inch deck gun. A total of 71 boats were constructed of this class and its slightly improved successors of the V class. Although they were useful boats in the early part of the war, the later examples diverted resources from construction of more effective vessels. Britain also built some 36 midget submarines; with 4-man crews, these vessels attacked ships at anchor in harbor.
France constructed three series of submarines in the period between the wars: large oceangoing long-range vessels for worldwide service and for operation with the fleet, smaller boats for offensive patrols in European waters, and a successful group of minelayers. The first postwar French submarines were of the 1922 and 1923 programs and were based on the study of German U-boats taken as reparations. These 9 submarines of the Requin-class had a standard surface displacement of 947 tons and were armed with 10 x 21.7-inch torpedo tubes, 1 x 3.9-inch deck gun, and 2 x 25.2 mm machine guns. The 31 large submarines of the Redoutable-class (launched between 1928 and 1937) generally were regarded as very effective boats. They displaced 1,384 tons standard on the surface; their maximum range was 10,000 miles at 10 knots on the surface, and their submerged endurance was 60 hours at 2 knots. They had a battery of 11 torpedo tubes (7 of them in 2 remotely controlled trainable external mounts) with a total of 13 torpedoes and a single 3.9-inch deck gun.
The French also constructed several smaller seagoing patrol-type submarines. A 1922 building program called for 4 x 600-ton boats. These were the Sirène-class, 9 of which were eventually built. Several other patrol-type submarine classes were authorized in the years before the war, but not all were complete when France fell in June 1940. These submarines displaced between 600 and 900 tons. The Aurore-class, the last series of French submarines being constructed when World War II began, displaced 893 tons and were armed with 9 x 21.7-inch torpedo tubes (3 in an external remotely controlled trainable mount) plus a single 3.9-inch deck gun and 2 x 13 mm machine guns.
The French minelaying submarines of the Saphir-class displaced 761 tons on the surface and could cruise for 7,000 miles at 10 knots on the surface. They had a submerged endurance of 48 hours at 2 knots and could safely operate to a depth of 250 feet. They carried 5 torpedo tubes (3 in a trainable external mount) with 7 torpedoes, 32 mines, and a single 3-inch deck gun.
The French navy also operated the largest submarine in the world at the outbreak of the war. The Surcouf, designed for long-range commerce warfare, displaced 2,880 tons standard on the surface and had a range of 10,000 miles at 10 knots on the surface. It had a range of 60 hours at 2 knots submerged and could operate safely at a depth of 250 feet. The Surcouf's battery included no fewer than 12 tubes (8 in external mounts) with 22 torpedoes, 2 x 8-inch guns in a special turret mounting, and a seaplane stowed in a hangar and launched with a catapult. The Surcouf also was equipped with a special compartment to accommodate prisoners taken from intercepted vessels and a small motor launch to transport boarding parties. The submarine proved to be successful in peacetime, but it never operated as designed during combat because of the fall of France and the boat's subsequent loss in a collision.
At the outbreak of war in September 1939, the Soviet Union deployed the world's largest submarine force, with 168 boats in service. Soviet mass production of submarines began early and produced a wide variety of different types. There were two basic series of M-type coastal submarines, two basic medium submarine series (the S-type, derived from the same basic design as the German Type VII, and the Shch or Pike-type of indigenous origin), minelayers of the L-type, and long-range boats of the K-type.
The U.S. Navy took the process of type standardization the farthest, entering World War II with a single basic design that was improved but never replaced during the course of the conflict. These "fleet boats" emerged through the crystallization and synthesis of a series of designs produced to meet requirements for fleet submarines to accompany the battle fleet, cruiser submarines for long-distance raiding, and patrol submarines for offensive operations in the Pacific. Nine vessels (essentially experimental prototypes) in five classes were produced between 1921 and 1934, ranging in size from 1,100 tons to 2,700 tons standard on the surface. Overall, these submarines were not very successful, suffering problems with their diesel machinery, diving ability, and general reliability, but they provided valuable experience and data for an improved design.
The new series that began with the Porpoise-class of 1934 were of 1,310 to 1,475 tons standard on the surface. They introduced diesel-electric reduction drive, which proved vastly more reliable than previous arrangements. Surface cruising range was 11,000 miles at 10 knots, and they had a patrol endurance of 75 days. They could operate for up to 48 hours submerged at 2 knots and had a safe-operating-depth limit of 250 feet. A battery of 6 to 8 torpedo tubes with 16 to 24 torpedoes was fitted, along with a light deck gun. Between 1934 and 1940, 38 submarines of this group were constructed, and they formed the backbone of the American submarine force when the United States entered the war.
The Gato-class that followed became the first wartime standard class. Displacement rose to 1,526 tons, the torpedo tube battery increased to 10 tubes, and safe depth increased to 300 feet. They were followed by the very similar Balao-class; its deeper safe-operating depth of 400 feet was accomplished by substituting high-tensile steel for the mild steel used in earlier boats. The Tench-class introduced diesel-electric direct drive that brought about a very significant reduction in noise and internal machinery space, leading to the addition of 4 reload torpedoes to the outfit. A total of 221 submarines from these 3 classes were completed during or immediately after the war. Significant wartime modifications included reducing superstructure, adding radar, and enlarging the gun armament by fitting 4-inch or 5-inch deck guns and adding multiple light antiaircraft weapons.
Germans developed their submarines clandestinely, since the Versailles Treaty prohibited them such weapons. Design work continued for foreign navies, with production undertaken in the customers' yards under German supervision. The first new German submarine, U-1, was completed only five weeks after the repudiation of the Versailles Treaty on 29 June 1935.
The overwhelming majority of the 1,150 U-boats commissioned between 1935 and 1945 belonged to two groups: the so-called 500-ton Type VII medium boats and the 740-ton Type IX long-range submarines. The Type VIIC actually displaced between 760 and 1,000 tons on the surface; it had a cruising range of 6,500 to 10,000 miles at 12 knots on the surface and 80 miles at 4 knots submerged. It had a battery of 55 torpedo tubes with 14 torpedoes, an 88 mm deck gun, and ever-increasing numbers of light antiaircraft weapons. Almost 700 of these boats in all their variants entered service during World War II. The Type XIC actually displaced 1,120 tons; it had a cruising range of 11,000 miles at 12 knots on the surface and 63 miles at 4 knots submerged. It had a battery of 6 torpedo tubes with 22 torpedoes, a 105 mm deck gun, and ever-increasing numbers of light antiaircraft weapons. Almost 200 of this type and its variants were commissioned.
Germany also commissioned several other important types of submarines during the war. Among the most important were the Type X minelayers and the Type XIV supply boats. Both variants operated as resuppliers for the operational boats during the Battle of the Atlantic, providing fuel, provisions, medical supplies, reload torpedoes, and even medical care and replacement crew members. Consequently, they became prime targets for Allied antisubmarine forces, and few survived. The other major vessels were the radical Type XXI and Type XXIII boats designed for high submerged speed and extended underwater operation. Revolutionary streamlined hull shapes, greatly increased battery space, and the installation of snorkels allowed these boats to operate at submerged speeds that made them very difficult targets for Allied antisubmarine forces. However, confused production priorities and the general shortage of materials late in the war prevented more than a very few from putting to sea operationally.
Italian submarines were of four basic types: very large oceangoing cruiser submarines, large minelayers, large long-range patrol boats, and medium-size vessels. The cruisers were few in number and proved rather unsuccessful, especially as they were slow to dive; they saw little operational service. The minelayers were much more successful. They displaced between 1,054 and 1,305 tons standard on the surface, with a range of 8,500 miles at 9 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 330 feet. Armament included a battery of 6 to 8 torpedo tubes with 8 to 14 torpedoes, 36 mines, and 1 or 2 3-inch deck guns.
The 2 series of patrol submarines emerged as essentially standard designs immediately before the war began. The larger group displaced between 920 and 1,000 tons standard on the surface, with a range of 9,000 miles at 8 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 330 feet. Armament included a battery of 8 torpedo tubes with 12 torpedoes and 1 x 4-inch deck gun. The smaller group displaced between 650 and 680 tons standard on the surface, with a range of 5,000 miles at 8 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 330 feet. Armament included a battery of 6 torpedo tubes with 12 torpedoes and 1 x 4-inch deck gun. These smaller patrol submarines were very successful boats and performed well in the shallow, clear waters of the Mediterranean. The larger boats performed quite effectively in the Atlantic.
Japan constructed very large submarines intended to operate primarily as integral components of the battle fleet. The kaidai (admiralty) type design was based on a large German cruiser submarine from World War I, and the type evolved into a series of 24 boats in 5 classes, constructed between 1921 and 1935. These vessels displaced between 1,390 and 1,635 tons standard, had operating ranges between 10,000 and 14,000 miles at 10 knots, carried a battery of 6 to 8 tubes with 14 to 16 torpedoes, could operate submerged for 36 hours at 2 knots, and had a safe operating depth of between 200 and 250 feet. Japan also developed very large cruiser submarines of the junsen (cruiser) typebetween 1924 and 1938. These 8 huge vessels had standard displacements between 1,970 and 2,231 tons and an operational range of 24,000 miles at 10 knots on the surface. They could dive safely to 300 feet.
In 1939, Japan essentially standardized its large submarine type with a vessel design displacing about 2,100 tons and capable of cruising on the surface for 14,000 miles at 16 knots or 24,000 miles at 10 knots. They could dive to 330 feet. Three models were produced—a headquarters type emphasizing communications and command facilities, an attack type emphasizing torpedo armament, and a scouting type that added hangar space and a catapult for a small reconnaissance floatplane. Some 46 of these large submarines were constructed, plus 3 others that brought together the facilities of all 3 types into the sen-toku (special submarine) type, a single monster hull displacing 3,530 tons standard. Japan also constructed 10 final examples of the kaidai type early in World War II.
Japan also developed and constructed a series of medium submarines intended for coastal work. In addition, Japan expended considerable effort on the development of midget submarines: small boats with two-man crews intended for stealthy attacks on ports and roadsteads after they were transported close to the scene of operation by larger submarines. Finally, late in the war, Japan was developing submarines with high underwater performance, but these never entered service.
Technology played a major part in determining the effectiveness of submarines. Most navies encountered problems with their torpedoes early, especially those submarine arms that relied on magnetic rather than contact pistols. Radar development conferred a special advantage on Allied submarines in particular, offsetting the edge in optical quality possessed by German and Japanese vessels. U.S. submarines were almost unique in their level of habitability, and they were almost the only boats that featured full air-conditioning and adequate space for their crews to sleep. Sonar developed rapidly, as did countermeasures; some navies put considerable effort into stealth and self-defense measures by emphasizing use of wakeless electric torpedoes and special antiescort homing torpedoes. The course of the submarine war demonstrated that those arms that fell behind in the technological battle suffered disproportionately heavily in combat. Paul E. Fontenoy
Carpenter, Dorr, and Norman Polmar. Submarines of the Imperial Japanese Navy. Annapolis, MD: Naval Institute Press, 1986.; Friedman, Norman. U.S. Submarines through 1945: An Illustrated Design History. Annapolis, MD: Naval Institute Press, 1995.; Gardiner, Robert. Conway's All the World's Fighting Ships, 1922–1946. London: Conway Maritime Press, 1980.; Polmar, Norman, and Jurrien Noot. Submarines of the Russian and Soviet Navies, 1718–1990. Annapolis, MD: Naval Institute Press, 1991.; Rössler, Eberhard. The U-boat: The Evolution and Technical History of German Submarines. Annapolis, MD: Naval Institute Press, 1981.
Paul E. Fontenoy