Baltic Sea campaigns ( 1939 – 45 ) The Baltic Sea Campaigns were conducted by Axis and Allied naval forces in the Baltic Sea , its coastal regions , and the Gulf of Finland during World War II . After early fighting between Polish and German forces , the main combatants were Germany and Finland , opposed by the Soviet Union . Sweden ' s navy and merchant fleet played important roles , and the British Royal Navy planned Operation Catherine for the control of the Baltic Sea and its exit choke point into the North Sea . While operations included surface and sub - surface combat , aerial combat , amphibious landings , and support of large - scale ground fighting , the most significant feature of Baltic Sea operations was the scale and size of mine warfare , particularly in the Gulf of Finland . The warring parties laid over 60 , 000 naval mines and anti - sweep obstacles , making the shallow Gulf of Finland one of the most densely mined waters in the world . Participants . Finnish Navy . The Finnish Navy was a small professional force . Naval strength in 1941 consisted of : The Finnish Navy used several other vessels ( for example , Coast Guard vessels ) during the wars : " Kriegsmarine " . Initially , the German " Reichsmarine " — the " Kriegsmarine " s pre - war name — suffered from the limitations imposed by post - World War I treaty obligations ; by 1935 , however , Germany had signed the Anglo - German Naval Agreement , which allowed it to expand considerably . The name Kriegsmarine was adopted the same year . Though a large , powerful , and professional force , it had to divide its assets between several theaters of war , severely limiting the number and size of the ships it was able to deploy in the Baltic Sea . At the start of the operation Barbarossa on 21 June 1941 German naval forces in the Baltic Sea consisted of In September 1941 Germany formed the provisional Baltenflotte , which consisted of the battleship " Tirpitz " , cruisers " Admiral Scheer " , " Emden " , " Köln , " Leipzig " and " Nürnberg " , destroyers " Z25 " , " Z26 " , " Z27 " and the 2nd torpedo boat squadron . It had been tasked with destroying the Soviet Baltic Fleet should it try to escape to neutral Sweden . As this did not happen , and aerial reconnaissance showed severe damage to the remaining ships of the Soviet Baltic Fleet , the " Baltenflotte " was disbanded before October 1941 . Polish Navy . The relatively small Polish Navy suffered greatly from lack of funds , but still managed to field , at the outbreak of war : Soviet Baltic Fleet . The Soviet Baltic Fleet was the largest of the four fleets which made up the Soviet Navy during World War II , and was commanded by Vladimir Tributs throughout the war . Though initially having bases only in the eastern corner of the Gulf of Finland , the Red Banner Baltic Fleet was the largest naval power in the Baltic Sea . As World War II progressed , it was able to make use of naval bases in Estonia , Latvia and Lithuania , first under the terms of agreements forced by the Soviet Union in autumn 1939 , then by direct access to the bases following the occupation of the Baltic states in spring , 1940 . Gains from the Moscow Peace Treaty ( 1940 ) after the Winter War further helped the Soviet Baltic Fleet , as it acquired a base at Hanko , Finland , as well as the coast of the Karelian Isthmus . Liepāja and Tallinn were the main naval bases of the Baltic Fleet prior to Operation Barbarossa . Other Navies on the Baltic Sea . The Swedish Navy was the third largest in the Baltic Sea . Though Sweden stayed neutral during the war , its naval vessels escorted and protected convoys inside Swedish territorial waters , at times attacking hostile submarines with depth charges . Estonia , Latvia and Lithuania all had small naval forces before World War II . During the occupation and annexation of the Baltic states by the Soviet Union in 1940 these were attached to the Soviet Baltic Fleet . Campaigns on the Baltic Sea . Operations before 1941 . Invasion of Poland . The Polish navy participated in the Battle of Gdańsk Bay in 1939 . Most of its surface ships were evacuated to continue the war from Britain ( Operation Peking ) , but a few vessels remained in Poland and were sunk by German forces . Polish Submarines operated in the Baltic until either internment or escape to Britain ( see Orzeł incident ) in the Autumn of 1939 . Operations in 1941 . The Winter War and the occupation of the Baltic states had left the Red Banner Baltic fleet in a strong position . It was the largest navy on the Baltic Sea ( two battleships , two light cruisers , 19 destroyers , 68 submarines , and a naval air arm comprising 709 aircraft ) with bases all along the Baltic coast as well as in Hanko . In particular , the long and vulnerable southern coast of Finland was now exposed to the Soviet navy for its full length . The Finnish Navy had two branches , the old but well - maintained coastal fortifications built by the Russians before World War I ( Peter the Great ' s Naval Fortress ) , and the actual navy , consisting of two coastal defence ships , five submarines and a number of smaller craft . The " Kriegsmarine " could provide only a small part of its naval force , as it was tied up in the battle of the Atlantic . Germany ' s main concern in the Baltic sea was to protect the routes through the Archipelago Sea which supplied its war industry with vital iron ore imported from Sweden . The Soviet Navy was taken by surprise by the initial German assault on the USSR on 22 June 1941 , and suffered heavy losses during the evacuation from the Baltic States and Finland . The " Kriegsmarine " had started laying mines several hours before the actual start of the invasion , with immediate effect , the Soviet Baltic Fleet losing a destroyer to mines on the second day of the war . The rapid German advance forced the Soviet Navy to abandon its bases along the Baltic coast and evacuate towards Tallinn and Kronstadt . To guard against a breakout by the Red Fleet , the Germans deployed a large battlegroup - including the new battleship , cruisers , and destroyers - to the Baltic in August – September 1941 , and laid a series of minefields across the Gulf of Finland . As the Soviet fleet made no attempt to flee to the Atlantic or neutral Sweden , Germany eventually withdrew its capital ships . Later , the Finnish coastal defence ship was sunk by mines during Operation Northwind , a failed feint operation . Finnish submarines and surface forces repeatedly attacked Soviet convoys to and from Hanko , but with limited success , due to both strong Soviet resistance and equipment failures . A report from Hanko told of a transport arriving with two unexploded Finnish torpedoes jutting from its hull . As naval bases at Riga and Liepāja were lost to German advances , the Soviet Navy withdrew to Tallinn , which was surrounded by the end of August , forcing the Soviets to conduct an evacuation by sea . To counter this , the German and Finnish navies dropped 2 , 400 mines , adding to the 600 already in the sea lanes outside Tallinn . German artillery was set up at Juminda peninsula and Finnish and German torpedo boat s were put on alert . The Soviet evacuation consisted of 160 ships , which carried 28 , 000 people ( including the Communist leadership and their families , army and navy personnel , and 10 , 000 Estonians ) and of materiel . The evacuation began on the night of 27 August , at the same time as the first German troops entered the city . During embarkation the ships were under constant attack by German bombers and artillery , which continued as the armada reached the heavily mined Juminda peninsula . At midnight on the 28th the armada ran into the minefields while being attacked by Finnish and German torpedo boats . Casualties were heavy , with 65 of the 160 ships lost , and several more damaged . Of the 28 , 000 evacuees , 16 , 000 perished . With relatively small means , the " Kriegsmarine " and Finnish Navy had dealt a severe blow to the Red Banner Baltic Fleet , which withdrew to the relative safety of the naval mine barriers and coastal fortifications of Kronstadt . At the start of the war Finnish ground troops isolated the base at Hanko , with its 30 , 000 - man garrison . The front there remained static , with only small scale naval and amphibious actions in the surrounding archipelago . By the end of the summer the Finnish 17th Division , which had made up the bulk of the besieging force , left Hanko for Eastern Karelia . By December 1941 the base was evacuated , having lost its importance due to both the continuing blockade and the rapid German advance toward Leningrad . The evacuation was performed in several convoys , which managed to transport roughly 23 , 000 troops to Leningrad . The fleet suffered casualties from Finnish minefields and coastal artillery , losing three destroyers and two large transports ( " Andrei Zhdanov " and " Iosif Stalin " ) as well as several smaller vessels . Finnish troops took the abandoned and heavily mined Hanko after the Soviets had left . Though naval mines , aerial supremacy , and the rapid German advance on land had largely neutralized its heavy elements , the Soviet Baltic Fleet in the immediate vicinity of Leningrad had not been destroyed . Shore bombardment by the fleet was important in saving Leningrad from the Initial German assault in September . The battleship " Marat " was sunk by German Junkers Ju 87 " Stuka " dive bomber s in Kronstadt on 23 September , but was partially salvaged for use as a static battery . Many Baltic Fleet sailors fought on land during the Siege of Leningrad . Also , though some of the islands in the bay of Finland had been lost during 1941 , Admiral Tributs had decided to keep the islands of Seiskari and Lavansaari , which would prove to be important bases as the war progressed . Operations in 1942 . In 1942 , the Baltic Fleet was confined to the innermost part of the Gulf of Finland by German minefields . The Soviets maintained the Oranienbaum Bridgehead and sent several submarines into the open Baltic via Lavansaari island , which now proved an invaluable base for both submarines and light surface forces . Submarines attacked German - Finnish as well as neutral shipping with limited success , sinking 18 ships but losing 12 submarines . Although the losses incurred by the Soviet submarines were fairly light , their presence in the Baltic Sea disrupted transportation and forced vessels to use safer coastal waterways instead of faster open sea routes . Continued Soviet submarine operations forced the Germans and Finns to step up their anti - submarine efforts in the Gulf of Finland , and largely due to these efforts , Soviet submariners met increasing hardships and losses , while seeing ever - fewer victories against Axis shipping . The Soviets had evacuated most of the islands in the Gulf of Finland in late 1941 . They recaptured the Suursaari from a small Finnish detachment in January 1942 ; two months later , a larger Finnish force with strong air cover marched over the ice and drove off the Soviet garrison . Soviet attempts to regain the island resulted in battles which continued over the ice until April 1942 . Finnish and German forces also captured lightly defended Tytärsaari . In July 1942 , the Soviets attempted to wrest the small island of Someri from the Finnish . In spite of initial success , the Soviet landing force was crushed , and the supporting naval units were repulsed in what proved to be one of the largest surface actions seen on the Baltic Sea during World War II . Finnish submarines spent most of early 1942 on the docks , where they were fitted with improved listening devices and weapons systems . In October 1942 , the boats were deployed to the Sea of Åland to hunt Soviet submarines which had managed to break through the anti - submarine barriers . Each of three large Finnish submarines managed to destroy one Soviet submarine , of which two were destroyed with torpedoes , and one by intentional ramming . Anti - submarine efforts on the Sea of Åland proved effective enough for the Soviet command to decrease submarine operations in the area . In November 1942 , Finnish motor torpedo boats raided the harbor of Soviet - controlled Lavansaari , sinking the gunboat in shallow water . The Soviets were able to recover and repair the ship , and after several months it was returned to active duty . Operations in 1943 . In the Spring of 1943 , the Axis completed an extensive mine and anti submarine net barrage across the Gulf of Finland , effectively preventing Soviet submarines from raiding German shipping or disrupting U - boat training . Six Soviet submarines were lost trying to penetrate the barrage . Operations in 1944 . The Soviets began to defeat the Axis on land in 1944 , lifting the Siege of Leningrad and relieving the Oranienbaum Bridgehead in January . In February 1944 , a Soviet amphibious assault on the south coast of the Gulf of Finland was repelled . Resisting at the Estonian border , the Axis maintained a minefield blockade until September , when Finland signed peace with the Soviet Union , and Army Group North retreated from Estonia . The " Kriegsmarine " lost several minesweepers and the anti - aircraft cruiser in the process . Three German " Elbing " - class torpedo boats — " T - 22 " , " T - 30 " and " T - 32 " — were also lost after running into a minefield in August 1944 . During the Soviet offensive against Finland in the summer of 1944 , the Red Army made landings in the Koivisto islands . Finnish and German naval units clashed with Soviet light naval units and were subjected to repeated air attacks , during which the Finnish Navy lost " Tarmo " and " VMV 17 " , Germany lost " T 31 " and " AF 32 " , and both had several other vessels damaged . Finnish forces were evacuated from the islands unchallenged , which opened the way for Soviet amphibious operations on Viipuri Bay . Finnish and German light naval forces made repeated raids into the bay , under constant air , artillery and motor torpedo boat attacks . While no ships were lost during the raids , nearly all participating vessels were heavily damaged . The naval forces never reached their target area , but their raids helped the defense of the islands in Viipuri Bay by drawing artillery fire , as well as attacks by Soviet aircraft . After the Allied invasion of Normandy ( D - Day ) , " Großadmiral " Karl Dönitz transferred the bulk of the German surface fleet to the Baltic in order to support the seaward flank of the German Army . The heavy cruiser bombarded Red Army positions near Riga , and several U - boats infiltrated the Gulf of Finland , losing six boats to the Soviets . Following Finland ' s Armistice with the Soviets , the Germans tried to seize strategic positions in Finland . In the Baltic , this included the failed operation " Tanne Ost " and the canceled operation " Tanne " West . In late August and September the Germans abandoned Estonia , successfully evacuating 91 , 000 soldiers and 85 , 000 civilian refugees by ship . This , combined with the use of Finnish bases and coastal seaways , enabled the previously impenetrable anti - submarine barrier to be circumvented by the Soviets . During the Moonzund Landing Operation , the Red Army and the Baltic Fleet took the Baltic Islands in September , and completed their operations in Estonia by the end of October . The " Kriegsmarine " opposed this offensive by bombarding the Red army , losing the destroyers " Z35 " and " in December . Operations in 1945 . In 1945 , as the Red Army advanced further into Nazi territory , the German Navy was involved in evacuating refugees and bombarding the Soviets . The Soviet surface fleet remained in the Leningrad area due to minefields and the poor condition of the ships , but Soviet submarines were very active , sinking the liners " Wilhelm Gustloff " , and " Goya " , which were evacuating refugees from East Prussia , with heavy loss of life . Operations on Lake Ladoga . Before World War II , Soviet and Finnish naval strength on Lake Ladoga ( fi . " Laatokka " ) was limited by the 1920 Treaty of Tartu , which restricted the maximum displacement of ships to and the maximum weapon caliber to . Operations in 1939 – 1940 . Lake Ladoga became part of the battleground during the Winter War , though it remained frozen for most of that conflict , limiting the use of naval forces on the lake . As the winter progressed , troop and supply movements across the ice became increasingly important , the Finns having surrounded a large Soviet formation on the northern shore of the lake , near Kitilä , in a motti . Unlike many other encircled Soviet formations , the forces in Kitilä were able to survive due to supply routes running across the ice . Finnish forces tried repeatedly to halt these operations by both fortifying islands next to the ice road and cutting cracks into the ice . Operations in 1941 – 1944 . When Operation Barbarossa and the Continuation War began , Lake Ladoga became a battleground once more . The Soviets ' first task was the evacuation of Red Army troops trapped against the northern shore of the lake by advancing Finnish forces . These withdrawals were for the most part successful , with Soviet forces sustaining only minor losses . After the German push toward Leningrad had besieged the city , the supply routes across the lake became of paramount importance to the Soviet defenders . As ice formation prevented ships from transporting supplies , ice roads were made on the lake - ice , forming the Road of Life . By the summer of 1942 , the Finns had moved only the obsolete MTB " Sisu " to Ladoga . The rest of their naval force consisted of small civilian boats and transport vessels captured from the Soviets . Germany and Italy also sent some naval forces to Ladoga , forming Naval Detachment K . Using mainly Italian motor torpedo boat s and German artillery barges and minelaying boats , the naval detachment tried several times to interdict the Leningrad supply convoys on Ladoga . They were transferred away as the lake began to freeze over , and did not return the following year , as the Soviets had managed to open a land route to Leningrad in January 1943 . The Finns bought several of the German barges and infantry boats and used them on Ladoga ; they also bought the Italian motor torpedo boats and used them in the Baltic . In 1943 there was little naval activity on the lake . In 1944 , however , the Soviet offensive across the River Svir ( aimed at capturing Sortavala at the lake ' s northern end ) included a landing at Tuloksa on the eastern shore . One Soviet naval infantry brigade was landed , and later reinforced by a second . Soviet air and naval superiority prevent Finnish naval forces from challenging them ; however , as the Soviet offensive continued , the Finnish flotilla - reinforced by three obsolete motor torpedo boats and three additional barges acquired from the Germans - supported the land forces with their artillery and countered Soviet raids at the northern end of the lake . When a ceasefire was declared , most of the Finnish naval assets were evacuated via land routes over the agreed - upon border . The Soviets demanded the former German barges and infantry boats , and received them in August 1945 at Helsinki . Operations on Lake Onega . When Finnish forces reached Lake Onega ( fin . " Ääninen " ) in 1941 they captured several Soviet ships , and raised others which had been sunk in shallow water by the retreating Soviets . Some of these were armed by the Finns . A captured Soviet naval vessel renamed " VTV - 1 " ( patrol gunboat nr . 1 ) was brought to Onega to support naval operations ; however , most of the ships available to the Finns were obsolete and unable to challenge even the small Soviet force that operated on the lake . Having determined that chances of successfully challenging Soviet naval forces during open - water season were low , the Finns emphasized long range patrols to attack Soviet boats while they were still docked . Their first successful operation took place on the frozen lake in Spring of 1942 , when a Finnish patrol crossed the ice and set fire to some Soviet barges . Small skirmishes continued throughout 1942 . In a notable engagement on 4 September , three Finnish ships escorting a tug engaged an armed Soviet steamer , and later two patrol boats , with inconclusive results . During the winter of 1942 - 1943 Onega did not freeze properly , which prevented actions over the ice . Another inconclusive encounter between Soviet and Finnish naval forces took place on 13 September 1943 . The Winter of 1943 - 1944 was also fairly warm , enabling ships to sail throughout the season on Onega . Since the transport network on shore was of relatively limited utility , the main task of Finnish naval forces had been to protect the transportation of materials over the lake . When the Soviets began their 1944 offensive in the Karelian Isthmus , the Finns , anticipating another offensive closer to Onega , had already begun evacuating the region . From 16 through 27 June , Finnish naval forces successfully protected the evacuation convoys , after which the ships were disarmed and scuttled . Only " VTV - 1 " was spared , being transported by rail to the Baltic . Soviet naval forces started their attacks on Onega on 26 June , and by the time they landed troops at Petrozavodsk on 28 June , the Finns had already left the area .