Battle of Svensksund The Battle of Svensksund ( Finnish : " Ruotsinsalmi " , Russian : " Rochensalm " ) was a naval battle fought in the Gulf of Finland outside the present day city of Kotka on 9 July 1790 . The Swedish naval forces dealt the Russian fleet a devastating defeat that resulted in an end to the Russo - Swedish War of 1788 – 90 . The victory has been named the biggest Swedish naval victory of all time . Background . Circumstances in the 1780s , including the war between Russia and the Ottoman Empire , and the moving of a portion of the Russian Baltic Fleet to the Black Sea , prompted the Swedish King , Gustav III to attack the Russian Empire in 1788 . It was also initiated to distract domestic attention from domestic political problems and for the king to be able to fulfill his role as a successful and powerful monarch . Gustav ' s main aim was to recapture some of the territory in Finland that had been lost to the Russians in the disastrous war of 1741 - 43 . In 1788 , he launched a surprise attack against the Russian fleet , intending to catch it by surprise . The plan was to attack Kronstadt and land a force to assault the capital of St Petersburg . The war was intended to be short and to be won by the assault on St Petersburg , conducted by the navy and " skärgårdsflottan " ( the " archipelago navy " ) . The latter , officially designated as " Arméns flotta " ( " navy of the army " ) was a separate branch of the armed forces designed for coastal operations and amphibious warfare in the Baltic . Since its formation in 1756 , it had been something of an elite within the Swedish armed forces . However , after the Battle of Hogland ( 1788 ) ( a tactical tie but a strategic failure for the Swedes ) Gustav lost the initiative and tensions in Sweden rose . The first battle of Svensksund on 24 August 1789 ended in a Swedish defeat . Prelude . In 1790 an attempt to assault Vyborg failed , and the Swedish navy along with King Gustav himself was caught in the Bay of Viborg . It managed to escape during the " Viborg gauntlet " on 3 July , though with heavy losses to the deep - sea navy . After retreating to Svensksund , King Gustav made a decision to make a stand there . Swedish coastal fleet was reinforced by 40 ships under Lieutenant - Colonel Carl Olof Cronstedt after the escape from Vyborg . Gustav made the decision to lead the fight personally and divided his forces into four brigades under lieutenant - colonels Carl Olof Cronstedt , Claes Hjelmstjerna , Victor von Stedingk , and Jakob Törning . Von Stedingk was to lead the center consisting of 2 hemmema ( " Styrbjörn " and " Starkotter " ) and 2 udema ( " Torborg " and " Ingeborg " ) archipelago frigates , brig " Alexander " , 15 galley s , 2 half - galleys , and 11 cannon or mortar longboats . Törning had the command of the right wing and had a force consisting of 39 gun sloops and 22 gun yawls while Hjelmstierna ' s left wing had 30 gun sloops and 14 gun yawls supported by 12 gun sloops and yawls from Cronstedts brigade . Rest of Cronstedts brigade , consisting of turuma " Norden " , 1 galley and 36 gun sloops and yawls , was to remain in reserve and guard possible Russian flanking maneuver . Artillery batteries were constructed to the skerries of Kråkskär ( between center and right wing ) and Sandskär ( between center and left wing ) . On 8 July the preparations were completed . Russian coastal fleet consisted of 9 archipelago frigates , 13 xebecs , 2 mortar ships , 4 gun prams , 3 floating batteries , 26 galleys , 6 schooners , 4 cutters , 77 gun sloops and 121 lightly armed boats . Russian fleet carried around 900 cannons compared to 450 Swedish cannons and had clear superiority in both number of ships and men . The Russian coastal fleet was eager to attack , especially on 9 July , the anniversary of Catherine the Great ' s proclamation as Empress of Russia . Recognizing the failure to decisively defeat the Swedish archipelago fleet a year earlier at the same location , Nassau - Siegen chose to commit his whole force from the south . This was done to prevent the Swedes from escaping to the shelter of Svartholm fortress since Nassau - Siegen was expecting a clear victory , having numerical superiority in ships , artillery as well as in men . On the morning of 9 July Gustav III suddenly named Lieutenant - Colonel Cronstedt as his flag - captain after relieving the Colonel George de Frese from his duties . Reason for this sudden chance was likely that de Frese had been in favor of withdrawing from Svensksund into more favorable location while Cronstedt had advocated fighting the Russians at Svensksund . Battle . At 0800 on 9 July 1790 the Russian flagship signaled the attack . By 0930 the first ships had reached firing distance in the western flank but soon after fighting had spread throughout the battle lines . The Swedish right wing under Lieutenant Colonel Törning met with increasing resistance as Russian left wing opposing him got reinforced . However the Swedes were able to move ships their reserves to support their right wing with a counterattack which managed to led the Russian left wing into disorder . Meanwhile the increasingly strong southwesterly wind forced the Russian center deeper between converging Swedish lines . After no Russian ships were seen approaching from Frederiskhamn the Swedes were able to release more ships from reserves to bolster the Swedish left wing led by Lieutenant Colonel Hjelmstierna . Half of the Hjelmstierna ' s ships were sent to the rear of the Russian fleet through narrow passage between Legma and Kutsalö which in turn forced Russian right wing to deploy accordingly . However movement to back of the line was read as signal to withdraw in Russian left wing which started its retreat leaving Russian center to face Swedes alone . By the evening it had become apparent that Swedes were victorious even though Russian center consisting of their galleys and largest ships continued to fight despite of unfavorable winds and battle damage . At this time the Swedes were able fire at the Russian ships from the front as well as from both sides and several Russian ships started drifting into the Swedish battle line while others other caught fire or were intentionally set on fire while a few were beached to avoid sinking . At 2000 ordered Naussau - Siegen to withdraw and to destroy drifting Russian ships to prevent them being captured . Strong winds made the withdrawal difficult and several ships failed to make it . A few of the Russian ships ignored the order to withdraw and instead kept fighting until they sunk . Fighting didn ' t end until 2200 . However the wind calmed down during the night and several Russian ships tried to escape under the cover of darkness but Swedish gun sloops and yawls were sent to hunt then down and this type of fighting continued until 0900 on the morning of 10 July 1790 . The Russians lost around 7 , 400 of at least 14 , 000 men dead , wounded and captured , compared with Swedish losses of one udema , four minor vessels and 300 men . Though others place the number of dead and wounded Swedes to around 600 . Among the Russian ships that were lost were 10 " archipelago frigates " ( sail / oar hybrids ) and xebec s , 9 " half - xebecs " ( schooners ) , 16 galleys , 4 gun prams and floating batteries , 7 bomb vessels , 5 gun sloops and several other small vessels . Along with 21 other ships the Swedes captured the " Catarina " , flagship of Nassau - Siegen . The battle of Svensksund is the biggest naval battle ever fought in the Baltic sea : 500 ships ( including supply ships and other ships not involved in combat ) , over 30 , 000 men and several thousand cannons . At Svensksund , the Swedes boasted to have destroyed 40 percent of the Russian coastal fleet . It qualifies among the largest naval battles in history in terms of the number of vessels involved . Aftermath . Surviving Russian ships were gathered to Frederikshamn where the badly depleted fleet was being rebuilt while Swedish coastal fleet stayed at Svensksund . Swedes did sent later a squadron of 25 gun sloops closer to Frederikshamn but they were turned back on 5 August by the rebuilt Russian coastal fleet . Swedes withdrew back to Svensksund but Russians did not give chase . This defeat encouraged Russia to negotiate with Sweden eventually signing the Treaty of Värälä on 14 August 1790 . Neither side gained any territory , however all provisions in the peace treaty of Nystad from 1721 that formally infringed upon Swedish sovereignty were cancelled . After the war the Russians started a massive fortification programme on the eastern , Russian , side of the Kymi river , building the sea fortress Fort Slava and the land fortress Kyminlinna . The forts later grew into the port city of Kotka . Sankt Nikolai . The Russian frigate " Sankt Nikolai " was sunk in the battle . She was found in 1948 almost intact off Kotka . Over 2 , 300 objects have been recovered from her hull by divers .