The Battle of Fehmarn 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. 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 of13 October 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 admiralPeter 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 flagship 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 flagship Patentia. The Danish admiral Pros Mund was killed during the fighting. The Swedish fire shipMeerman 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 17 October.
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 Royal Swedish Navy. 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 13 August 1645.
