The 'Action of 6 December 1941' was an engagement between Soviet and Bulgarian naval forces in the Black Sea in the area off the Bulgarian coast at Cape Emine (6 December 1941).
When the Axis invasion of the USSR got under way on 22 June 1941, Bulgaria did not declare war on the USSR and made no contribution to the land invasion. The country did offer naval support to the Axis, however, in allowing Axis warships to use Bulgarian ports and even use three of its torpedo boats (including Drazki) to escort Romanian warships as they laid mines along the Bulgarian coast in October 1941. These actions made the Bulgarian coast a target for the Soviet warships of Vitse Admiral Filipp S. Oktyabrsky’s Black Sea Fleet.
On 1 December 1941, several Soviet submarines, including the 'Shchuka' class Shch-204, commanded by Captain Gricenko, were sent to patrol along the Axis coastline. On 6 December, Shch-204 was spotted near Cape Emine, 20 miles (32 km) off Varna, by Arado Ar 196 single-engined floatplanes of the Bulgarian air force. The Bulgarian submarine chasers Belomorets and Chernomorets were quick to reach the scene and together with the floatplanes attacked the Soviet submarine with depth charges, soon sinking her with all hands.
This engagement was the most significant Bulgarian naval victory of World War II, and Shch-204 was the only Allied submarine sunk by the Bulgarian navy. Through this victory, the Bulgarian navy demonstrated its availability and capability of working together with its German and Romanian counterparts in the Black Sea for the defence of Axis coastlines and convoys.
It is worth noting that non-Bulgarian sources describe the loss of Shch-204 as the result of hitting a mine on this day. A Russian author has averred that the submarine chasers were at Burges at the time of the claimed engagement for work on their engines. Some Russian sources claim that the submarine was lost to a German Heinkel He 59 floatplane or to just a Bulgarian Ar 196 floatplane.