The Ukrainian MoD announced that as a result of an attack, a Project 636.3 submarine, B-237 Rostov-na-Donu, was sunk in the Sevastopol Port. The attack hit the Russian Black Sea Fleet home both metaphorically and technically, as Sevastopol is the fleet's headquarters. Rostov-na-Donu was hit in the past by a cruise missile attack from Ukrainian aircraft and had to be taken to extensive maintenance.
Rostov-na-Donu, as a Project 636.3 (Improved Kilo-class II) attack submarine, posed a significant threat to Ukraine with its capability to fire Kalibr land attack cruise missiles. Ukraine doesn't have the means to perform anti-submarine warfare, and it has no suitable ships or aircraft for such missions.
Thus, it has to rely on intelligence and its long-range missiles and kamikaze UAVs to attack the Black Sea Fleet-affiliated submarines in their most open state. However, it is unclear how Ukraine conducted the attack. Beyond the attacks on submarines, other Russian warships and support ships have also taken their share from the Ukrainian stand-off attacks in several cases.
