Black Sea Fleet
Russia's southern fleet, based in Crimea since 1783, the reason Moscow wanted the peninsula back, and the force a country with no navy has beaten out of it.
Russia has always had a geography problem: its coastline is long, and most of it is frozen, landlocked, or both. The Black Sea is the exception, a warm-water outlet that leads through the Turkish straits to the Mediterranean and the world. The fleet that guards it was founded in 1783, the year Catherine the Great annexed Crimea, and Grigory Potemkin built a new base for it at a spot he named Sevastopol. Everything Russia has done in Crimea since, including in 2014, follows from wanting to keep that base.
Defeats that shaped Russia
The fleet's history is a record of being bottled up. In the Crimean War, unable to face British and French steam warships at sea, the Russians sank their own ships across the mouth of Sevastopol harbor to block the entrance, and the peace of 1856 forbade Russia from keeping a fleet in the Black Sea at all, a humiliation Alexander II spent fifteen years undoing. In 1905 the mutiny aboard the battleship Potemkin became a symbol of imperial decay and, later, one of the most famous films ever made. In 1918 the fleet was scuttled again, this time on Lenin's orders to keep it from the Germans.
The constraint that never went away is the geography. The Montreux Convention of 1936 gives Turkey control of the straits and lets it close them to warships in wartime, which means the Black Sea Fleet can be locked in or locked out by a country that is now a NATO member. A fleet in the Black Sea is powerful against its neighbors and irrelevant everywhere else.
Divorce and repossession
When the Soviet Union broke up, the fleet and its bases sat in newly independent Ukraine. It took six years to settle: a 1997 partition treaty gave Russia the large majority of the ships and leased it the main Sevastopol facilities until 2017. In 2010 President Viktor Yanukovych extended the lease to 2042 in exchange for cheaper Russian gas, a deal Ukrainian opposition members fought over on the floor of parliament. Four years later, after Yanukovych fled, Russia annexed Crimea outright. The soldiers who took the peninsula's airports and parliament came in significant part from the forces already legally stationed there.
Losing a sea war to a country with no navy
Ukraine began the 2022 invasion with essentially no warships, having scuttled its own flagship. It has nonetheless driven the Black Sea Fleet out of the western Black Sea. On April 14, 2022 Ukrainian Neptune missiles hit the cruiser Moskva, the fleet's flagship, which sank under tow. Drone boats packed with explosives, cruise missiles, and long-range strikes on Sevastopol followed, including a hit on the fleet headquarters in September 2023. By October 2023 Russia was moving major units east to Novorossiysk, and Ukraine had lost or damaged a substantial fraction of the fleet, including landing ships and submarines.
The strategic consequence was immediate: Ukraine reopened a maritime corridor for its grain exports without a navy protecting it, simply by making the sea too dangerous for Russian warships. For a fleet that exists to project power over its neighbors, that is a more serious defeat than the sinking of any single ship, and it is the strongest evidence yet that cheap precision weapons have made large surface ships in enclosed seas a liability rather than an asset.