The flagship of Russia's Black Sea Fleet, the Moskva, lies at the bottom of the sea.
Ukraine says the Russian warship, which was sailing off the coast of Odesa, was destroyed Thursday by one of its missiles.
A US official has supported Ukraine's version of events, saying they believe the Moskva was downed by a Ukrainian Neptune anti-ship missile.
Still, Russia's defence ministry has not confirmed this. They said the warship sunk while being towed to port, following a fire onboard, which involved ammunition stored in the hull.
In any case, the Moskva is now out of action - for good. But what impact, if any, will this have on the war in Ukraine?
The Moskva, equipped with surface-to-air missiles, provided long-range and mobile air defence for the whole of Russia's fleet in the Black Sea. It protected cruisers, frigates, missile corvettes and amphibious landing ships capable of carrying thousands of troops.
Without the Moskva's defensive firepower, this fleet will be more vulnerable to attack, especially from the Ukrainian Air Force.
Nevertheless, Russia has powerful air defence systems deployed in Crimea, which it seized from Ukraine in 2014. These can defend the fleet against attack as it operates in the area.
Russia will not be able to replace the capabilities of the Moskva any time soon. It only has two other ships of the same class - the Marshal Ustinov and the Varyag - which serve with Russia's Northern and Pacific fleets respectively.
To reach the Ukrainian theatre, both would need to pass through the Bosphorus into the Black Sea. The waterway between Istanbul is controlled by Turkey, which says it will not let warships from any state pass through.
"When Turkey is not a belligerent in the conflict, it has the authority
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