The Regia Marina (Royal (Italian) Navy) dates from the proclamation of the Kingdom of Italy (Regno d'Italia) in 1861 after Italian unification (il Risorgimento). In 1946, with the birth of the Italian Republic (Repubblica Italiana), the Regia Marina changed its name to Marina Militare, ((Italian) Navy) as it was now the navy of the Italian Republic.
Read more about Regia Marina: Origins, World War I, Interwar Years, World War II, After World War II, The Peace Treaty