Russia's Black Sea fleet, based in Crimea for 240 years, is at risk of losing its flagship naval hub as Ukraine steps up attacks. The assaults have forced Russia to move its ships further from harm's way. Ukraine's success at sea is notable because it lacks its own warships, instead challenging Russia's naval supremacy using missiles and unmanned maritime drones. The Ukrainian attacks have increased pressure on Russian defenses in Crimea and on supply lines to its troops in occupied southern Ukraine.