According to the findings of the military portal Jene's 360, on March 27, the Turkish ship noticed a Russian submarine of Kilo type (project 636.3, Warszawianka) flowing north towards the Bosphorus strait. Earlier, on March 14, the Turks noticed the south of the straits, dividing Europe and Asia, another Russian submarine of the same type.
The Russian submarine, identified at the end of March, is probably a unit called "Nowogród Wielki", and the one noticed in the middle of last month was "Krasnodar". Both ships are Kilo units. In the first half of March, the commander of the 4th Independent Brigade of Submarines, part of the Black Sea Fleet, reported that two submarines - "Krasnodar" and "Old Oskol" are preparing to go out into the sea for a longer period.
The above facts indicate the truthfulness of the thesis made in the media for some time that the Russian underwater presence off the coast of Syria is permanent and rotational. Still in 2018, when the security situation in that country was much more inflamed, it was pointed out that the presence of Russian ships, including submarines, was to serve as a "shield" for the possible deployment of US Navy units and American allies in this area.
Just over half a year ago, in August 2018, Russia sent the largest group of ships to the eastern Mediterranean since the end of the Cold War. This movement occurred shortly after the Kremlin said that the United States and their allies are considering another wave of attacks on objects belonging to the Syrian President Bashar Al Assad regime.
The above actions took place during the planned operation of the Syrian government forces against the rebels in the Idlib province. American security adviser John Bolton warned then that the United States would react "very strongly" to the possible use of chemical weapons by the Al Assad regime. Such strikes have occurred before, in April 2017 and 2018, in response to the use of this type of weapon against forces fighting Syrian government troops.