The Glauco class was a pair of submarines ordered by the Portuguese government, but were taken over and completed for the Regia Marina during the 1930s. They played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists.
Delfino was one of four Squalo-class submarines built for the Regia Marina during the late 1920s. The boat served in World War II and was sunk in 1943 after a collision with another Italian ship.
The Squalo-class submarines were a group of four submarines built for the Royal Italian Navy during the 1930s. They were built at the Cantieri Riuniti dell'Adriatico (CRDA) shipyard at Monfalcone, and designed by Curio Bernardis.
Domenico Millelire was one of four Balilla-class submarines built for the Regia Marina during the late 1920s.
Balilla was the lead ship of her class of four submarines built for the Regia Marina during the late 1920s.
Antonio Sciesa was one of four Balilla-class submarines built for the Regia Marina during the late 1920s. She played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists.
Foca was the lead ship of her class of three submarine minelayers built for the Regia Marina during the late 1930s.
Zoea was one of three Foca-class submarine minelayers built for the Regia Marina during the late 1930s.
The Settembrini class was a pair of submarines built for the Regia Marina during the late 1920s. They played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists.
The Pisani-class submarines were built for the Regia Marina during the late 1920s. They played a minor role in the Spanish Civil War of 1936–1939 supporting the Spanish Nationalists.
Argonauta was the lead ship of her class of seven submarines built for the Regia Marina during the early 1930s.
Salpa was one of seven Argonauta-class submarines built for the Regia Marina during the early 1930s.
Serpente was one of seven Argonauta-class submarines built for the Regia Marina during the early 1930s.
Des Geneys was one of four Pisani-class submarines built for the Regia Marina during the late 1920s. Due to her age, her usefulness was limited, and she saw no real service during World War II. The submarine was decommissioned in 1942 and converted into a battery-charging hulk.
Giovanni Bausan was one of four Pisani-class submarines built for the Regia Marina during the late 1920s. Due to her age, her usefulness was limited, and she saw no real service during the war. The submarine was decommissioned in 1942 and converted into an oil barge.
Squalo was the lead ship of her class of four submarines built for the Regia Marina during the late 1920s. The boat served in World War II and was decommissioned in 1948.
Tricheco was one of four Squalo-class submarines built for the Regia Marina during the late 1920s. The boat served in World War II and was sunk in 1942 by the British submarine HMS Upholder.
The Bragadin-class submarines were built for the Regia Marina during the late 1920s. Both boats participated in the Second World War and were discarded in 1948.
Marcantonio Bragadin was the lead ship of her class of two submarines built for the Regia Marina during the late 1920s. The boats participated in the Second World War and was discarded in 1948.
Filippo Corridoni was one of two Bragadin-class submarines built for the Regia Marina during the late 1920s. The boat participated in the Second World War and was discarded in 1948.
Italy 
