The battle of Køge (or Kjøge) Bay was a naval battle of the Great Northern War. It took place in the period after the battle of Poltava, when there was a real danger that Sweden would be invaded. Indeed one Dnaish army had already landed between Helsingborg and Landskrona, but had been defeated at Helsingborg (10 March 1710). By the autumn of 1610 a force of 6,000 Russian troops was at Danzig, ready to launch a new invasion.
The main Danish fleet spend much of this time patrols between Køge Bay (south of Copenhagen) and the island of Bornholm, at the entrance to the Baltic. In the middle of September that fleet, under General Admiral Count Gyldenløve, had made an attempt to reach Danzig, but had been turned back by a gale. The transport fleet at Danzig had been ordered to sail west without an escort. Gyldenløve had then been ordered back to Bornholm, but before he could leave news arrived that the Swedish fleet was at sea, and due to the poor condition of their ships the Danes were forced to remain in Køge Bay.
The Danish fleet contained twenty six ships, carrying 1,808 guns. The largest ship was the Fredericus IV of 110 guns. The Swedish fleet was smaller, with 21 ships and 1,512 guns, commanded by Admiral Wachtmeister. Its largest ship was the Enighet of 94 guns. Although they were outnumbered, the Swedish ships were in better condition, having just left harbour. The Danish ships in Køge Bay were mixed in amongst some transport ships, and were unable to form up a single line of battle.
The Swedish fleet reached Køge Bay on the morning of 4 October. At first the Danes believed them to be the transport fleet from Danzig, but by 11.00 am they had been identified as hostile. The wind was blowing from SE by E, almost directly into the bay, potentially trapping the Danes in the bay. The Danish fleet formed up into a number of separate lines, before tacking into the wind in an attempt to present a strong front against the Swedes. Instead the Danish fleet became somewhat scattered, with a group of five ships nearest to the Swedes.
The Swedes were able to advance in a more organised way, sailing into the bay before forming a line. At 2.30 the Swedish flagship, the Götha Lejon, opened fire. The two lines did not overlap evenly. The Götha Lejon was at the centre of the Swedish line, but only the ships behind her were able to join in the battle.
The only casualty of the battle was the Danish 94 gun ship Dannebroge. She caught fire early in the battle, possible as a result of sparks from her own fire. At 3.30, after an hour of fighting, she exploded. Only three of the crew survived.
That ended the fighting. The Swedish line was coming close to the shoals at the northern end of the bay, and was forced to tack. Two Swedish ships ran aground. Efforts to re-float them the next day failed, and the Swedes were forced to burn them to prevent them falling into Danish hands. Having tacked, the two fleets briefly attempted to form new lines of battle, but the weather was closing in, and at five p.m. the Swedish fleet anchored to ride out the storm.
At the end of 5 September the Danes must have been satisfied with the outcome of the fighting. Although they had lost one ship in the battle, the Swedes had lost two run aground. However, on 6 September the balance swung dramatically in favour of the Swedes. The transport fleet at Danzig and obeyed the order to sail without an escort, although without the Russian troops. On 6 September they sailed straight into the Swedish fleet. Twenty four ships were captured, one destroyed and fourteen run aground. The next day the Swedish fleet sailed away to the east, shadowed briefly by the Danish fleet.
Although the battle of Køge Bay was itself an indecisive affair, the loss of the transport fleet and the advancing season combined to protect Sweden from invasion, at least until Charles XII had returned from his exile in the Ottoman Empire in 1714.