The Battle of Heligoland (or Helgoland) 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, and , 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 and and the corvette .