The Type IX U-boat was designed by Nazi Germany's Kriegsmarine in 1935 and 1936 as a large ocean-going submarine for sustained operations far from the home support facilities. Type IX boats were briefly used for patrols off the eastern United States in an attempt to disrupt the stream of troops and supplies bound for Europe. It was derived from the Type IA, and appeared in various sub-types.
German Type XXIII submarines were the first so-called elektroboote to become operational. They were small coastal submarines designed to operate in the shallow waters of the North Sea, Black Sea and Mediterranean Sea, where larger Type XXI electric boats were at risk in World War II. They were so small they could carry only two torpedoes, which had to be loaded externally. As with their far larger sisters—the Type XXI—they were able to remain submerged almost all of the time and were faster than conventional U-boats, due to the improved streamlining of their shape, batteries with larger capacity and the snorkel, which allowed the diesel engines to be used while submerged. The Type XXI and XXIII U-boats revolutionized post-war submarine design. Nearly a thousand Type XXIII boats were projected towards the close of World War II, but most of these were either cancelled, scrapped incomplete, or only projected.
The Loch class was a class of anti-submarine (A/S) frigate built for the Royal Navy and her Allies during World War II. They were an innovative design based on the experience of three years of fighting in the Battle of the Atlantic and attendant technological advances. Some shipyards had trouble building these larger ships, which led to widespread use of the Castle-class corvette, introduced around the same time.
Imperial Japanese Navy submarines originated with the purchase of five Holland type submarines from the United States in 1904. Japanese submarine forces progressively built up strength and expertise, becoming by the beginning of World War II one of the world's most varied and powerful submarine fleets.
At the outbreak of the Second World War Nazi Germany's Kriegsmarine had 21 destroyers in service, while another one was just being completed. These 22 vessels – comprising 3 classes – had all been built in the 1930s, making them modern vessels. Including that final pre-war vessel, a further 19 were brought into service during the war and more were captured from opposing navies, including the Italian Navy after the Italian Armistice with the Allies in 1943.
The Torpedoboot Ausland were small destroyers or large torpedo boats captured by Nazi Germany and incorporated into the Kriegsmarine. They were assigned a number beginning with TA.
A merchant submarine is a type of submarine intended for trade, and being without armaments, it is not considered a warship like most other types of submarines. The intended use would be blockade running, or to dive under Arctic ice.
The Marcello class was a class of nine submarines built in 1937 and 1938 by CRDA in Trieste for the Royal Italian Navy. Two similar submarines built in 1939 at La Spezia by Oto Melara are sometimes considered part of the class. All eleven served in the Mediterranean Sea at the start of the Second World War. After Provana's 1940 sinking, the remaining boats were transferred to the BETASOM Atlantic submarine base at Bordeaux in August 1940. After four boats had been sunk in the Atlantic, Barbarigo and Comandante Cappellini were then selected for conversion to "transport submarines" in order to exchange rare or irreplaceable trade goods with Japan. Cargo capacity of 160 tons reduced reserve buoyancy from 20–25% to 3.5–6%; and armament was reduced to defensive machine guns. Only Dandolo was in operational condition at the end of the war.
The Redoutable-class submarines were a group of 31 submarines built between 1924 and 1937 for the French Navy. Most of the class saw service during the Second World War. The class is also known in French as the Classe 1 500 tonnes, and they were designated as "First Class submarines", or "large submarine cruisers". They are known as the Redoutable class in reference to the lead boat Redoutable, in service from 1931 to 1942. The class is divided into two sub-class series, Type I, known as Le Redoutable and Type II, Pascal.
The Cagni or Ammiraglio Cagni class was a class of submarines built for Italy's Regia Marina during World War II.
The CB class was a group of midget submarines built for the Italian Navy during World War II. However, they were also used by several other navies, seeing action in the Mediterranean and in the Black Sea.
Italian submarine Luigi Torelli was a Marconi-class submarine of the Italian navy during World War II. The vessel operated in the Atlantic from September 1940 until mid-1943, then was sent to the Far East. After Italy's surrender in 1943, the Luigi Torelli was taken over by Nazi Germany's Kriegsmarine, then, in the waning months of the war, the Japanese Imperial Navy. It was one of only two ships to serve in all three major Axis navies, the other being the Italian submarine Comandante Cappellini.
The Élan class was a class of French minesweeping sloops. Originally designed as minesweepers, they were never used in that role, instead being used mostly as escort vessels. Built between 1936 and 1940, the first came into service just before the outbreak of World War II.
German submarine U-476 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
The Chamois class were French minesweeping sloops ordered between 1935 and 1939. They were similar in design to the Élan class, and like them classed as minesweepers, but were actually used as anti-submarine ships, convoy escorts and patrol vessels.
Sava was a Flutto-class submarine in service with the Yugoslav Navy. Built by Cantieri Riuniti dell'Adriatico in Monfalcone during the Second World War, Sava was laid down and completed as Nautilo for service with the Italian Regia Marina.
The German torpedo boat TA37 was an Ariete-class torpedo boat operated by the German Kriegsmarine during the Second World War. The ship was built for the Italian Navy by the shipbuilder CRDA at their Trieste shipyard with the name Gladio in 1943, but was incomplete when Italy surrendered to the Allies in September 1943, and was seized by Nazi Germany. The ship entered service as TA37 in 1944, serving in the Adriatic and Aegean seas and was sunk by British destroyers on 7 October 1944.
Regia Marina 
