Battle of Åland Islands
1915 CE.
Shown on the map at 57.442°, 18.975°.
The Battle of Gotland, which occurred in July 1915, was a naval battle of World War I between the German Empire and the Russian Empire, assisted by a submarine of the British Baltic Flotilla. It took place in the Baltic Sea off the shores of Gotland, Sweden, a country neutral in World War I.
Text from the Wikipedia article Battle of Gotland, licensed CC BY-SA 4.0.