ST. PETERSBURG, May 5. /TASS /. The sixth Project 636.3 diesel-electric submarine Kolpino designed for the Russian Black Sea Fleet will be put afloat in St. Petersburg on May 31, a source in the Navy Main Command told TASS on Thursday.

"The submarine Kolpino is set to be floated out on May 31," the source said.

Russia’s United Ship-Building Corporation told TASS earlier that the submarine is expected to be put afloat in May. However, the corporation did not specify the exact date.