Russia's 'Silent Killer' Kilo-Class Submarine Moving Toward Black Sea As War Tensions Mount

As Russia's troop buildup on the Ukraine border enters a dangerous stage, reports emerge that a Russian Kilo-class submarine has crossed the Bosphorus strait, toward the Black Sea.

The extremely silent and improved submarine Rostov-na-Donu (Project 636.3) has crossed the 30-km-long strait from Turkey's inland Sea of Marmara and was accompanied by a Turkish coast guard vessel during its passage, reported Naval News.

The submarine, belonging to the Black Sea Fleet, was seen entering the Black Sea bordering Ukraine, days after Russia's six amphibious warfare vessels entered the waters. This includes three Ropucha-class amphibious assault ships Minsk, Korolev and Kaliningrad, which can carry troops, tanks and supplies.

Russia claims the Project 636.3 submarines are among the world’s quietest submarines and are the third generation of large diesel-electric submarines.

An upgraded version of Project 877 subs, the Project 636.3 submarines are nicknamed the 'Black Hole' and silent killer by the U.S. Navy for their stealth. The kilo-class submarines are also equipped with torpedo tubes with 18 torpedoes and eight surface-to-air missiles. The torpedo tubes can also deploy 24 mines.

According to Forbes, the improved Kilo-class submarines make the Black Sea Fleet a major undersea power in the region, after the Turkish Navy.

Besides, Rostov-No-Donu is also equipped with the Kalibr land-attack cruise missile that can play a significant role in case of a "limited assault." The report added that if Putin opts for "a shallower ground assault that secures local gains near the border," then the Kalibrs could be the main weapons and this will make the Kilos the main shooters.

Though Russia claims the vessels are said to be in the Black Sea for a pre-planned drill that began Saturday and involves 30 Russian ships, there are concerns that the reinforcement of the Black Sea Fleet hints at the upcoming invasion.

Meanwhile, Ukraine on Sunday advised airlines to avoid flying over the open waters of the Black Sea due to the Russian naval exercises taking place there. "From tomorrow, airlines are advised not to fly ...over this area, and to plan optimal routes in advance, taking into account the current situation," Ukraine's state air traffic service said. However, it said the airspace over the territory of Ukraine remained open.

Russia too has warned mariners to avoid significant portions of the northern end of the Black Sea and Sea of Azov this week. Though this is ostensibly due to the naval drill planned by Russia in the region, there are concerns that this could mean a "de facto blockade" of Ukraine's southern coastlines.