Second Schleswig War: The Battle of Heligoland (depicted), the last naval engagement fought by squadrons of wooden ships, took place between the Danish and Austro-Prussian fleets.

The Second Schleswig War, also sometimes known as the Dano-Prussian War or Prusso-Danish War, was the second military conflict over the Schleswig–Holstein question of the nineteenth century. The war began on 1 February 1864, when Prussian and Austrian forces crossed the border into the Danish fief Schleswig. Denmark fought troops of the Kingdom of Prussia and the Austrian Empire representing the German Confederation.

The Battle of Heligoland was fought on 9 May 1864, during the Second Schleswig War, between a Danish squadron led by Commodore Edouard Suenson and a joint Austro-Prussian squadron commanded by the Austrian Commodore Wilhelm von Tegetthoff. The action came about as a result of the Danish blockade of German ports in the North Sea; the Austrians had sent two steam frigates, SMS Schwarzenberg and Radetzky, to reinforce the small Prussian Navy to help break the blockade. After arriving in the North Sea, Tegetthoff joined a Prussian aviso and a pair of gunboats. To oppose him, Suenson had available the steam frigates Niels Juel and Jylland and the corvette Hejmdal.