Short answers, pulled from the story.
The Imperial Russian Navy was officially founded on the 20th of October 1696, when the Boyar Duma passed a decree to begin constructing a navy following Tsar Peter the Great's use of warships and galleys in the Second Azov campaign against Turkey that year. The navy operated until it was dissolved in 1917 following the February Revolution.
At its peak in the early 19th century, the Imperial Russian Navy ranked third in the world by fleet size, behind only Britain and France. The Black Sea Fleet alone held 35 line-of-battle ships and 19 frigates in 1787, and the Baltic Fleet had 23 ships of the line and 130 frigates in 1788.
At the Battle of Tsushima on the 27th of May 1905, Admiral Togo intercepted the Russian Baltic Fleet in the Tsushima Strait after its voyage of over 18,000 miles from Europe. By the end of that day, nearly all of Admiral Rozhestvensky's battleships were sunk. The following day, Admiral Nebogatov surrendered the remaining ships, dropping Russia from third to sixth place among the world's naval powers.
On the 1st of January 1905, the Imperial Russian Navy established the world's first operational submarine fleet at Vladivostok, using seven submarines as its foundation. Russia's first submarine, purchased from Isaac Rice's Electric Boat Company and renamed Som, was commissioned in 1904, and the fleet's first combat patrol took place on the 14th of February 1905.
The Imperial Russian Navy was divided among the Baltic Sea, the Black Sea, the Russian Far East, and the Arctic, with no easy way for fleets to reinforce one another. Baltic ports including Saint Petersburg froze in winter, as did Vladivostok, and the Black Sea Fleet could not freely pass through the Ottoman-controlled Bosphorus and Dardanelles. This geographic isolation meant separate fleets developed independently and could not coordinate during crises.
In the Black Sea, the Russian fleet achieved near-complete dominance by the end of 1915, harassing Ottoman shipping and nearly cutting off coal supplies to Constantinople. In the Baltic, Germany held the upper hand and the Russian fleet played a mainly defensive role, suffering a major German incursion during Operation Albion in October 1917. By 1917 the navy had accumulated a fleet of 55 submarines used with varying success.