By August 1941 the German Army Group North was on the outskirts of Leningrad, having occupied the Baltic states and northwest Russia, while the Finns had advanced south into the Viipuri peninsula, leaving the city surrounded and cut off from all communication by land.

Against this, the Axis had little response; their only offensive force was a single Finnish ship, the torpedo boat Sisu, which was unable to interrupt the Soviet supply route.

Already on the lake was the Finnish torpedo boat Sisu, and a German force, Naval Detachment K, composed of a number of minesweepers (KM) and armed barges (Siebel ferries).

The XII MAS commenced operations on 25 June 1942, making reconnaissance sweeps across the lake, landing observers behind Soviet lines, and searching for submarines.

Following its 1000-mile journey to its area of operations, XII MAS served on Lake Ladoga for a 90-day period, making 59 sorties, and engaging in 17 actions, during which they sank Soviet barges, a gunboat (Bira class) and a merchant ship of 1300 tons.

Despite the skill and enthusiasm which the MAS brought to this corner of the Eastern Front, the combined operation was unable to stop Soviet efforts to maintain supply route to Leningrad,[1] and the winter of 1942/43 saw the Sinyavino offensive and Operation Iskra, which led to an easing of the Soviet supply dilemma, though the siege was not completely lifted until January 1944.