Security Service of Ukraine (SBU) said a domestically produced Sub Sea Baby underwater drone struck and critically damaged a Project 636.3 Kilo-class diesel-electric submarine in the port of Novorossiysk, leaving the vessel out of action and confined to port.The SBU released video footage that appears to show the drone impacting the hull and triggering a large explosion, and said the submarine carried four launchers for Kalibr cruise missiles Moscow has repeatedly used in long-range strikes on Ukrainian civilian infrastructure and energy facilities.Kyiv framed the operation as part of an asymmetrical maritime campaign that, together with Sea Baby surface drones used in operations that drove Russian ships from Sevastopol Bay, has forced much of Russia's Black Sea Fleet into mainland ports and demonstrated how relatively low-cost uncrewed systems can impose strategic costs on higher-value naval assets, a development analysts say will require new naval defence and countermeasures and carries risks of escalation.