Short answers, pulled from the story.
The Regia Marina emerged on the 17th of March 1861 following the unification of various Italian state navies. The new navy inherited a chaotic mix of equipment and standards primarily from the Kingdoms of Sardinia and Naples.
In 1897, the Regia Marina experimented with radio communications using Guglielmo Marconi's technology. By 1903, naval officer Vittorio Cuniberti published an article envisioning the all-big gun battleship design that would later become known as the dreadnought.
On the 11th of November 1940, British aircraft sank three Italian battleships during a surprise raid against Taranto harbor. Albert Kesselring observed that the Regia Marina functioned well only in fair weather conditions due to conservative leadership hindering critical technologies like radar and sonar.
On the 2nd of June 1946, a popular referendum abolished the Italian monarchy and established the Republic. This political shift caused the Regia Marina to officially become the Marina Militare, marking the end of over eighty years of royal service.
A peace treaty signed in Paris on the 10th of February 1947 imposed severe restrictions including a total displacement cap of 67,500 tons excluding battleships. Italy could not own battleships, aircraft carriers, submarines, or amphibious assault units under these terms.