The Ukrainian military says it sank a Russian submarine during an attack on the port of Sevastopol in Russian occupied Crimea. Kyiv says it also damaged an advanced air-defense system. Ukraine also says it attacked an airbase inside Russia, hitting ammunition stored there. Verified video shows huge explosions at the Morozovsk airbase, more than a hundred kilometers from the Ukrainian border. This comes as Russian troops have made sustained gains in the eastern Ukrainian region of Donetsk.00:00 Ukraine attacks inside Russia01:20 DW speaks with Christopher Morris, security expert at the University of Portsmouth05:40 DW speaks with military analyst Frank Ledwidge in Oxford