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.