Second Schleswig War: The Danish navy defeats the Austrian and Prussian fleets in the Battle of Heligoland.

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 19th century. The war began on 1 February 1864, when Prussian and Austrian forces crossed the border into the Danish fief…