Danish and Austrian naval units clash in the North Sea at the Battle of Heligoland
The Second Schleswig War saw the Danish Navy control the North Sea. An Austrian squadron was organised and appeared in the English Channel in early May. A smaller Danish squadron met the Austrians, and their Prussian allies off the British island of Heligoland in the afternoon and after a sharp action, forced them to withdraw. The six-month war, however, ended in defeat for the Danes in July 1864. (By John Osborne)
Michael Embree, Bismarck's First War: The Campaign of Schleswig and Jutland 1864 (Solihull, England: Helion and Company, Ltd, 2007), 282-285.