The battle of Gotland-Öland was a chaotic two day battle during the Nordic Seven Years War. A Danish fleet under Herlof Trolle had been at sea since the start of May. Off Bornholm it was joined by six ships from Lübeck, bring the combined fleet up to twenty seven ships. The allied fleet then sailed north through the Baltic. On 30 May the fleet was between the islands of Öland and Gotland, when it encountered the Swedish fleet.
That fleet was probably twenty three ships strong, and was commanded by Jakob Bagge. His flagship, the Mars (also known as the Makalos or the Jutehatar) was the biggest ship in the Baltic, carrying a massive 173 guns. When the battle began both fleets were somewhat scattered and the fighting was between small clusters of ships.
The main fighting on the first day was concentrated about the massive Mars and two ships that remained close to her. She was attacked by Herlof Trolle on his flagship, the Fortuna. The Danish fleet was still using boarding tactics, but the Mars was protected by booms which made boarding difficult. The Fortuna was driven off with her main yard destroyed while a Lübeck ship was sunk.
On the second day the Mars was once again isolated, this time with three supporters. Once again the Danes concentrated on the Mars, led by Trolle in the Fortuna. Once again the Fortuna was driven off, but this time the Mars was boarded from both sides from both Danish and Lübeck ships. Soon after being boarded, the Mars caught fire and then shortly after that exploded, killing most of her crew as well as 300 of the boarders. Bagge was amongst the survivors.
With their flagship lost the Swedish fleet withdrew to Elfsnabben to make repairs. The rest of the fleet had suffered very little damage in the battle, and the Swedish fleet was back at sea during July.