The Battle of Dybbøl (Danish: Slaget ved Dybbøl; German: Erstürmung der Düppeler Schanzen) was the key battle of the Second Schleswig War, fought between Denmark and Prussia. The battle was fought on the morning of 18 April 1864, following a siege that began on 2 April. Denmark suffered a severe defeat which – with the Prussian capture of the island of Als – ultimately decided the outcome of the war, forcing Danish cession of the duchies of Schleswig and Holstein.