The Regia Marina (RM) or Royal Italian Navy was the navy of the Kingdom of Italy from 1861 to 1946. In 1946, with the birth of the Italian Republic, the Regia Marina changed its name to Marina Militare.
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 Marconi class was a class of six submarines built for the Royal Italian Navy. The submarines were all launched between 1939 and 1940, and all but one, Luigi Torelli, were lost in the Atlantic during the Second World War.
Carlo Fecia di Cossato was an officer in the Regia Marina, in command of submarines and torpedo boats during World War II. He was credited with the confirmed sinking of 23 enemy ships. He was also a recipient of the Knight's Cross of the Iron Cross and of the Gold Medal of Military Valor, the highest decoration of the Italian Armed Forces.
BETASOM was a submarine base established at Bordeaux, France by the Regia Marina during the Second World War. From this base, Italian submarines participated in the Battle of the Atlantic from 1940 to 1943 as part of the Axis anti-shipping campaign against the Allies.
The Cagni or Ammiraglio Cagni class was a class of submarines built for Italy's Regia Marina during World War II.
Leonardo da Vinci was a Marconi-class submarine of the Italian navy during World War II. It operated in the Atlantic from September 1940 until its loss in May 1943, and became the top scoring non-German submarine of the entire war.
The Italian submarine fleet of World War II was the largest in the world at the time, with 116 submarines. It saw action during the Second World War, serving mainly in the Mediterranean. During the conflict 88 submarines, 75% of its total strength, were lost.
Operation Neuland was the code name of the Kriegsmarine extension of unrestricted submarine warfare into the Caribbean Sea during World War II. U-boats demonstrated range to disrupt United Kingdom petroleum supplies and United States aluminum supplies which had not been anticipated by Allied pre-war planning. Although the area remained vulnerable to submarines for several months, U-boats never again enjoyed the opportunities for success resulting from the surprise of this operation.
Archimede was a Brin-class submarine built for the Royal Italian Navy during the 1930s.
The Argo-class was a class of two coastal submarines built by Cantieri Riuniti dell'Adriatico in Monfalcone for Portugal but operated by the Royal Italian Navy after Portugal was unable to pay construction costs. The submarines were built in 1936, and both served in the Mediterranean Sea at the start of the Second World War. The boats were transferred to the BETASOM Atlantic submarine base at Bordeaux in 1940, but returned to the Mediterranean in 1941, where both were sunk within a few days of the September 1943 Italian armistice.
The Liuzzi class was a class of four submarines built by Tosi in Taranto for the Royal Italian Navy. The submarines were built in 1939 and began their Second World War service in the Mediterranean Sea, where Liuzzi was sunk. The three surviving boats were transferred to the BETASOM Atlantic submarine base at Bordeaux in 1940. After Tarantini was sunk, Bagnolini and Giuliani were 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 between 20 and 25% to between 3.5 and 6%; and armament was reduced to defensive machine guns. The submarines saw action in the Second World War during which they collectively sunk 5 freighters and 1 light cruiser and were eventually either sunk or captured.
Giuseppe Finzi was one of three Calvi-class submarines built for the Regia Marina during the 1930s. Completed in 1936, she played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists. The submarine made multiple patrols in the Atlantic Ocean during the Second World War, sinking five Allied ships. Gisueppe Finzi began conversion into a transport submarine in 1943, but was captured by the Germans in September 1943 before it was completed and redesignated as UIT-21. She was scuttled by them in August 1944 to prevent her capture.
Pietro Calvi was the lead ship of its class of two submarines built for the Regia Marina during the 1930s. Completed in 1936, she played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists. The submarine made multiple patrols in the Atlantic Ocean during the Second World War, sinking seven Allied ships. Pietro Calvi was rammed and sunk by a British convoy escort in July 1942.
USCGC Chelan was a Lake-class cutter belonging to the United States Coast Guard launched on 19 May 1928 and commissioned on 5 September 1928. After 13 years of service to the Coast Guard, she was transferred to the Royal Navy as part of the Lend-Lease Act, and named HMS Lulworth (Y60). During the war Lulworth served in a convoy Escort Group for Western Approaches Command
Michele Bianchi was a Marconi-class submarine of the Italian Regia Marina that saw action in the Second World War. The submarine,, was launched on 3 December 1939.
Guglielmotti was a Brin-class submarine built for the Royal Italian Navy during the 1930s.
Enrico Tazzoli was one of three Calvi-class submarines built for the Regia Marina during the 1930s. Completed in 1936, she played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists. She operated in the Atlantic during the Second World War and was second only to the submarine Leonardo da Vinci as the highest scoring Italian submarine of the conflict. Enrico Tazzoli was converted in 1943 to be a submarine transport for blockade-running between Europe and the Far East. She was lost on her first voyage in this role. She had been pronounced missing on 17 May after loss of contact. Her loss has never been definitively explained.
Salvatore Bruno Todaro was an Italian naval officer and submariner during World War II. He is best known for his participation in the battle of the Atlantic and the two instances in which he towed to safety the lifeboats carrying the survivors of ships he had sunk.
Primo Longobardo was an Italian naval officer and submariner during World War II.
Regia Marina 
