Short answers, pulled from the story.
The Regia Marina was established on the 17th of March 1861, following the proclamation of the Kingdom of Italy. It was formed primarily from the navies of the former kingdoms of Sardinia and Naples, along with the other states of the Italian peninsula.
At the Battle of Lissa on the 20th of July 1866, the Italian fleet under Admiral Persano, despite outnumbering the Austrians in both ships and equipment, suffered a severe defeat. Italy lost two armored ships and 640 men to the Austrian force commanded by Admiral Wilhelm von Tegetthoff.
Admiral Domenico Cavagnari, appointed Chief of Staff of the Navy by Mussolini in 1933, actively discouraged the adoption of radar and sonar. He told Admiral Iachino to "proceed with extreme caution regarding brilliant technical innovations," calling such devices "traps in your way," even though Italian scientists including Ugo Tiberio and Guglielmo Marconi were conducting relevant research.
The Mignatta, codenamed "leech," was an early crewed torpedo carrying two men. On the 1st of November 1918, it entered the harbor of Pola and planted two magnetic mines that sank the Austro-Hungarian flagship, shortly after the entire Austrian navy had been transferred to the newly founded State of Slovenes, Croats and Serbs.
When the Regia Marina sailed its fleet to Allied ports following the 1943 armistice, a flotilla from La Spezia was intercepted by German aircraft. The battleship Roma was struck by two Fritz X guided glide-bombs and sunk, killing approximately 1,600 sailors including Admiral Carlo Bergamini, the Italian Naval Commander-in-Chief.
The peace treaty signed on the 10th of February 1947 banned Italy from owning battleships, aircraft carriers, submarines, and amphibious assault units. The total displacement of the future navy was capped at 67,500 tons and staff at 25,000 men. Italy also had to hand over three battleships, five cruisers, seven destroyers, six minesweepers, and eight submarines to the victorious powers.