F21 was an F-class submarine in commission in the Italian Regia Marina (Royal Navy) from 1918 to 1930. She took part in the Adriatic Campaign of
Design
Construction and commissioning
In July 1915, FIAT-San Giorgio laid down an F-class submarine for the Italian Regia Marina (Royal Navy) at Italy. Originally designated F21, that submarine was sold to Portugal and entered service in the Portuguese Navy as NRP Hidra.
To replace the first F21, the Regia Marina ordered a second submarine also designated F21. FIAT-San Giorgio laid down the second F21 at La Spezia on 1915. She was launched on 1918 and commissioned into service in the Regia Marina as F20 on 1918.
Service history After F21 completed workups, the Regia Marina assigned her to the Brindisi Submarine Squadron for operations in the southern Adriatic Sea during the Adriatic Campaign of Before the war ended in November 1918, she had carried out two war patrols along the coast of Austria-Hungary, but without significant results. After World War I, she participated in numerous training exercises and in naval maneuvers with surface warships.
F21 was decommissioned and stricken from the navy list on 1930. She subsequently was scrapped.
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