British submarine development also was influenced by the cruiser and fleet submarine concepts, though the manifestation of those ideas was almost entirely through evolution from designs existing at the end of World War I. The main thrust of early evolution between the wars centered on the overseas patrol type, displacing 1,475 tons on the surface, with 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 minelaying submarines of similar size also were built, as well as a small series of very fast large submarines for work with the fleet. Both of those developments, however, proved very costly and of limited operational utility.

In the early 1930s a fresh start was made with the Swordfish class, designed for offensive patrols in narrow waters. These boats displaced 640 tons standard, had a cruising range of 3,800 miles at 9 knots on the surface and 36 hours at 3 knots submerged, and 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, had a cruising range of 4,500 miles at 11 knots on the surface and 55 hours at 3 knots submerged, and 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 World War II on these two types, producing a total of 62 of the “S” type and 53 of the “T” type.

Just before World War II 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 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. It had 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. While they were useful boats in the early part of the war, later examples diverted resources from the construction of more effective vessels. Britain also constructed some 36 midget submarines, with four-man crews, for attacks on shipping at anchor in harbor.

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, few in number, proved rather unsuccessful, especially as they were slow to dive; they saw little operational service. The minelayers, however, 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 one or two 3-inch deck guns.

The two series of patrol submarines emerged as essentially standard designs immediately before World War II 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 one 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 one 4-inch deck gun. These smaller patrol submarines were very successful boats, performing well in the shallow, clear waters of the Mediterranean; the larger boats performed quite effectively in the Atlantic.

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 31 large submarines of the Redoutable class were generally regarded as very effective boats. They displaced 1,384 tons standard on the surface, with a maximum range of 10,000 miles at 10 knots on the surface and a submerged endurance of 60 hours at 2 knots. They had a battery of 11 torpedo tubes (seven of them in two remote- controlled, trainable external mounts), with a total of 13 torpedoes and a single 3.9-inch deck gun. The series of smaller patrol submarines began with 12 boats of the “600-tonne” type, followed by 30 of an improved “630-tonne” model, several of which were still incomplete when France fell in June of 1940. They had a range of 4,000 to 5,600 miles at 10 knots on the surface, an underwater endurance of 48 hours at 2 knots, and a safe operating depth of 330 feet. The torpedo battery comprised 9 tubes (three in an external, remote- controlled trainable mount) with a total of 9 torpedoes, plus a single 3.9-inch deck gun. The minelayers displaced 761 tons, could cruise for 7,000 miles at 10 knots on the surface, 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 (three 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 between the two world wars. The Surcouf was designed for long-range commerce war and displaced 2,880 tons standard on the surface, had a range of 10,000 miles at 10 knots on the surface and 60 hours at 2 knots submerged, and could operate safely at 250 feet. The Surcouf’s battery included no fewer than 12 tubes (eight in external mounts) with 22 torpedoes, two 8-inch guns in a special turret mounting, and a seaplane stowed in a hangar and launched with a catapult. The Surcouf was also 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 never operated as designed during combat because of the fall of France and the boat’s subsequent loss in a collision.

Soviet production of new submarines began in 1927. Clandestine cooperation with Germany gave Soviet engineers access to design data for German types from late World War I: minelayers, Type UBIII, and Mittel-U. The Soviets salved and recommissioned the sunken British submarine L-55, which gave them access to late-war British design information. Soviet designers also gained considerable data from rehabilitating the later czarist-era Bubnov-designed boats and the final examples of the ubiquitous Holland H-type submarines. Synthesizing this information permitted the Soviets to produce a wide variety of submarines on a large scale. There were two basic series of “M”-type coastal submarines, two basic medium submarine series—the “Shch” or Pike type of indigenous origin (though strongly influenced by British practice), and the later “S”-type derived from the same basic design as the German Type VII, minelayers of the “L”-type developed from the L-55, and long-range boats of the “K”-type. At the outbreak of World War II in September 1939, the Soviet Union deployed the world’s largest submarine force, with 168 boats in service.

The final “M”-type displaced 283 tons surfaced, had a range of 4,500 miles at 8 knots on the surface or 36 hours at 3 knots submerged, could dive to 295 feet, and had a battery of 2 torpedo tubes with 4 torpedoes and a 45mm antiaircraft gun. The developed “S”-type displaced 856 tons surfaced, had a range of 9,500 miles at 9 knots on the surface or 45 hours at 3 knots submerged, could dive to 330 feet, and had a battery of 6 torpedo tubes with 12 torpedoes and a 4-inch deck gun. Their indigenous rivals displaced 587 tons, had a range of 3,650 miles at 7 knots or 50 hours at 2.5 knots submerged, could dive to 295 feet, and carried 6 torpedo tubes with 10 torpedoes. The minelayers displaced 1,108 tons, had a range of 10,000 miles at 8.6 knots or 60 hours at 2.5 knots submerged, could dive to 330 feet, and carried 8 torpedo tubes with 14 torpedoes and 20 mines. The “K”-type were very popular with their crews and were regarded as the best Soviet submarines of World War II. They displaced 1,480 tons, had a range of 15,000 miles at 9 knots or 50 hours at 2.5 knots submerged, could dive to 330 feet, and carried 10 torpedo tubes with 24 torpedoes. Despite this variety, the Soviet Union’s yards produced large numbers of submarines during World War II, completing some 200 boats during the course of the conflict.