Second Schleswig War: Prussian victory at Dybbøl and Danish naval action at Heligoland

Background. The conflict arose from the November Constitution of 1863, which integrated Schleswig with Denmark, violating the London Protocol. Prussian and Austrian forces invaded in February 1864. Danish troops retreated to Dybbøl, where Prussian siege artillery began bombarding fortifications in March. The war concluded with the Treaty of Vienna in October 1864, resulting in Danish cession of Schleswig, Holstein, and Lauenburg.

Siege of Dybbøl. Prussian forces established siege positions in March 1864, firing approximately 65,000 shells by April 18. The bombardment targeted Danish fortifications and the town of Sønderborg. Danish defenders repelled an initial attack on April 4, but the Prussians moved into final assault positions on the morning of April 18, leading to the storming of the redoubts.

Naval Action at Heligoland. On 9 May 1864, a Danish squadron led by Commodore Edouard Suenson engaged a joint Austro-Prussian squadron commanded by Austrian Commodore Wilhelm von Tegetthoff. The Danish navy gained a tactical victory in this engagement, which is noted as the last significant naval battle involving wooden ships and Denmark.