Delfino was designed by marine engineer Giacinto Pullino at the La Spezia Navy Yard. Accounts vary as to the date of her construction; it seems that she was built as an experimental craft and was under trials for several years before being accepted by the Italian Navy.
Delfino was laid down in 1889, launched in 1890 and completed in 1892. She commenced trials on April 1892 which continued until April 1895, when she was commissioned into the Regia Marina. (Her official records say she was built between 1892 and 1895, and was commissioned in 1896)
Delfino was a single hull design, powered by a 65 hp Savigliano electric motor driving a single screw, giving a surface speed of 6kn and a submerged speed of, with a range of 24nmi cruising at . She was controlled by vertical rudders two aft and unusually one forward) and horizontal planes fore and aft. She also had two vertical axis propellers to power vertical movement underwater, but these proved to give little advantage. She was armed with one torpedo tube and had a complement of 8 crewmen.
Delfino was modernized between 1902 and 1904; she was equipped with a 130 hp FIAT petrol engine which increased her surface speed to, and her surface range to cruising at . The torpedo tube was changed to and her conning tower was enlarged for surface navigation.[1]
Delfino was commissioned on 1 April 1895 (official records say 1896) and she served with the Regia Marina into the 20th century. She was still in service at the outbreak of World War I and saw action in the Adriatic, carrying out some 44 war patrols, though she also served as a training vessel. At the end of hostilities Delfino was moved into reserve, and was stricken in January 1919.[1]