Battle of Heligoland Day in Denmark Date in the current year: May 9, 2024

The Battle of Heligoland was fought in the North Sea in 1864, during the Second Schleswig War, between a Danish squadron and a joint Austro-Prussian squadron. It shouldn’t be confused with similarly named battles that were fought in 1849 (First Schleswig War), 1914 (World War I), 1917 (again World War I), and 1939 (World War II).

The Second Schleswig War was the second military conflict fought for control over the German duchies of Schleswig, Holstein and Saxe-Lauenburg. After the death of King Frederick VII of Denmark, his successor Christian IX signed a new constitution, which dissolved the personal union between Denmark and Schleswig and made Schleswig part of Denmark. This caused outrage in the duchy and gave the German Confederation a justification for war.

On February 1, 1864, joint Austrian and Prussian forces crossed the border into Schleswig, beginning the Second Schleswig War. During the first months of the war, the Dutch navy blockaded German ports, including Hamburg, an important port on the River Elbe. Austria and Prussia had to recall their fleets stationed in the Mediterranean sea to German waters.

Having received information about the approach of Prussian and Austrian ships, the Danish squadron retreated to the Norwegian coast to replenish supplies. On May 5, it returned to the island of Heligoland, which was then a possession of neutral Great Britain. Thanks to friendly relations with the British government, the Danish received permission to stay near Heligoland, as wall as information about the number of Prussian and Austrian ships.

Upon learning that the enemy was not numerous, Commodore Edouard Suenson, who led the Danish squadron, decided to attack before the arrival of Austrian reinforcements. Commodore Wilhelm von Tegetthoff, commander of the joint Austro-Prussian squadron, also wanted to engage in battle as soon as possible in order to end the Danish blockade of German ports in the North Sea.

The two squadrons encountered each other off Heligoland on the morning of May 9. The Austrian flagship opened fire first, but the attack wasn’t very successful. Prussian gunboats weren’t able to effectively engage the Danish warships, since they were slow and lagged behind the Austrian vessels. By 16:00, the Austrian flagship suffered damage from shell hits and began to withdraw from the action to the British zone, followed by the rest of the Austro-Prussian squadron.

The Danish vessels suffered considerably smaller losses when the Austro-Prussian squadron: 14 men killed and 54 wounded, in contrast to 36 men killed and 108 wounded on the two Austrian frigates. The battle resulted in a tactical victory for Denmark. Since it was one of Denmark’s biggest naval victories (and the last time Danish warships fought a major action), the anniversary of the Battle of Heligoland was declared as an official flag day in Denmark.