Battle of Fehmarn ( 1644 ) The Battle of Fehmarn ( 1644 ) took place north - west of the island of Fehmarn , now part of Germany , in the Baltic Sea . A combined Swedish fleet , with a large element of hired Dutch ships , defeated a Danish fleet and took 1000 prisoners , including Ulfeldt , Grabov and von Jasmund . The Danish admiral Pros Mund was killed in the battle . The Swedes had 16 ships with 392 guns , and the Dutch element had 21 ships with 483 guns ( making a total of 37 ships with 875 guns ) . The Danes had 17 ships with 448 guns . The Swedes expended two fireships and the Dutch lost one ship . The Danes lost 10 ships captured , including their largest three , and two wrecked . The battle . On the morning of October 13 the Swedish - Dutch fleet weighed anchor and prepared for battle by dividing into two Swedish and three Dutch squadrons . One of the Swedish squadrons was led by Wrangel on " Smålands Lejon " and the other under vice admiral Peter Blum on " Draken " . The Dutch squadrons were commanded by Thijssen onboard " Jupiter " , vice admiral Henrik Gerretsen on " Groote Dolphijn " and Schoutbynacht Pieter Marcussen on " Groot Vliessingen " . The Danish fleet was divided in two squadrons under admiral Pros Mund on " Patentia " and Joachim Grabow on " Lindormen " . Around 10 am the larger ships in both fleets were within firing range of each other and started firing . The smaller Danish ships retreated from the battle , but were pursued by the Dutch ships . Early in the battle the Swedish flag ship " Smålands Lejon " was so damaged in her rigging and hull that she had to pull out . The Swedish ships " Regina " och " Göteborg " attacked and boarded the Danish flag ship " Patentia " . The Danish admiral Pros Mund was killed during the fighting . The Swedish fire ship " Meerman " was sent against the Danish " Lindormen " , which quickly caught fire and exploded . The wreck was discovered in 2012 . Swedish " Nya Fortuna " captured the Danish man - of - war Oldenborg by boarding . The last man - of - war " Tre Løver " veered off , but was pursued by Anckarhjelm ' s Dutch " Jupiter " , " Patentia " and " Swarte Arent " . " Tre Løver " managed to sink " Swarte Arent " before the two other Dutch ships boarded her . The smaller Danish vessels " Tu Løver " , " Havhesten " , and " Fides " were captured by Dutch " Jupiter " and " Groote Dolphijn " . A cluster of Danish ships were forced against the shore of Lolland , among them " Neptunus " , " Nellebladet " , " Stormarn " , and " Kronet Fisk " . These were later towed by the Dutch . Danish " Delmenhorst " went aground and exploded after being set on fire by the Swedish fire ship " Delfin " . Danish " Markatten " , " Højenhald " and a galleot also went aground , but cannon fire from land protected them from the Dutch . Only " Pelikanen " and " Lammet " managed to escape and sail to Copenhagen on October 17 . Consequences . The Danes lost twelve ships , of which ten were captured . A hundred men perished and about 1 , 000 were captured . The ship " Swarte Arent " was the only loss on the Swedish side ; its crew was rescued . In total , the Swedish side suffered only 59 deaths . The victory was one of the greatest in the history of the Swedish Fleet . Even if transshipping Torstensson ' s soldiers to the Danish islands was no longer a threat , since these were now intent on meeting general Gallas ' Imperial troops approaching from the south , the Danes realized that Sweden had total naval dominance after the battle . This paved the way for negotiations and eventually the treaty of Brömsebro on August 13 , 1645 .