MOSCOW, December 3. /TASS/. The Black Sea Fleet’s submarines Stary Oskol and Krasnodar currently on their deployment in the Russian Navy’s permanent Mediterranean taskforce will undergo planned repairs at the Kronstadt Marine Plant in the spring of 2020, a source in Crimean defense circles told TASS on Tuesday.

"The Kronstadt Marine Plant will carry out repairs of these submarines. The subs will arrive approximately in April," the source said.

The Admiralty Shipyard in St. Petersburg was earlier expected to repair the third and fourth submarines from the series of six Project 636.3 subs built for the Black Sea Fleet. Both the Admiralty Shipyard, which builds Project 636.3 subs and the Kronstadt Marine Plant are part of Russia’s United Shipbuilding Corporation.

In late April, the Krasnodar and the Stary Oskol passed through the Black Sea into the Mediterranean, replacing the same-type submarines Veliky Novgorod and Kolpino in the Russian Navy’s Squadron in that area. The latter submarines operated off the coasts of Syria for a year and a half. The rotation of their crews was held every three months. The fifth and sixth submarines of this Project stayed in the Mediterranean Sea after their inter-fleet passage from the Baltic Sea.

The first planned repairs of the first, second, fifth and sixth submarines of this series have already been performed or will be carried out at the Sevastopol Marine Plant (a branch of the Zvyozdochka Ship Repair Center).

The Admiralty Shipyard has built a series of six Project 636.3 diesel-electric submarines for the Black Sea Fleet. Three of them, the Veliky Novgorod, the Kolpino and the Rostov-on-Don, numerously delivered strikes with Kalibr-PL cruise missiles against terrorist targets in Syria.

Project 636.3 submarines are referred to the third generation of diesel-electric subs. These submarines are considered among the world’s most noiseless vessels. They develop a speed of up to 20 knots, can dive to a depth of about 300 meters and their sea endurance is 45 days. The sub has a crew of 52 men and displaces about 4,000 tonnes.