The Prussian-Austrian occupation of Sønderborg in Denmark in April 1864 was the beginning of the Danish annus horribilis. Over a century and a half ago, Denmark fought a battle for the southern part of Jutland – the Battle of Dybbøl – and lost.
The conflict that led to the war in 1864 had roots that went all the way back to Medieval times, when Schleswig (the southernmost part of Jutland and northernmost part of Germany) became a duchy with special laws. It was the duty of the duke of Schleswig to protect Denmark against foreign tribes threatening the southern border of the country.

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The Danish annus horribilis
The Battle of Dybbøl was the key battle of the Second Schleswig War and occurred on the morning of 18 April 1864 following a siege starting on 7 April. Since the Danes had to load their old muzzle-loading rifles standing, they were easy targets for the Prussian army, which were equipped with breech-loading rifles that could be loaded while the user was lying down.
During the occupation, the need for the Jutland Danes to preserve their national identity became crucial and they gathered in the community hall to sing patriotic Danish songs and celebrate their Danish-ness. The battle of Dybbøl has had an enormous impact on the Danes’ self-perception and foreign politics ever since. The war is a complex part of the Danish history and has always been associated with tension and strong opinions.

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Rolf Krake – a mobile seaborne artillery platform
The attackers reached Dybbøl Mill and in a counter-attack the Danish 8th Brigade lost half their men, dead, wounded or captured. The Danes did, however, have one major advantage in that they were able to deploy the modern ironclad Rolf Krake to the scene to support Danish ground forces at Dybbøl with shore bombardments from its turret-mounted eight-inch guns.

For much of the siege, Rolf Krake was used as a mobile heavy seaborne artillery platform and the Prussians were almost helpless to counter it since they had no naval forces of their own capable of matching the Danish navy, a fact that sapped Prussian morale.
The official army casulaity list
Still, the last resistance, lasting for six intense hours, collapsed at the bridgehead in front of Sønderborg. After that there was an artillery duel across the Alssund.
A Danish official army casualty list at the time said: 671 dead; 987 wounded, of whom 473 were captured; 3,131 unwounded captured and/or deserters; total casualties 4,789. The 2nd and 22nd Regiments lost the most. Also, the crew of the Danish naval ship Rolf Krake suffered one dead, 10 wounded.
Dybbøl fort lies in a short blunt peninsula that defends against access to the fort by land and featured an enclosed pier for ferry across the Alssund to Sønderborg on the island of Als.

The Visitor Center at Dybbøl
After a referendum in 1920, southern Jutland was handed back to the Danes. Today, a visitor center attached to the windmill tell the story, while across the road, on the site of the Dybbøl Battlefield, a memorial pays homage to the fallen Danish soldiers.
The Battle of Dybbøl was the first battle monitored by delegates of the Red Cross.
The Danish Annus Horribilis, written by Tor Kjolberg