Stary Oskol ( Russian Старый Оскол ) is the name of a Russian, diesel-powered submarine from the 636 .3 project “Varshavyanka”. It was keeled in August 2012, launched in August 2014 and has been tested in the Barents Sea and the North Sea . In June 2016, the submarine began a longer surface voyage accompanied by the Russian tug “Altaj” to its operational area in the Black Sea as part of the Black Sea fleet . It was also observed in the English Channel by the Royal Navy .