It was the last major engagement of the war, as the Prussians under General Herwarth von Bittenfeld secured the island of Als – occupied by 9,000 Danish troops, including the garrison of Dybbøl which had retreated there – in a night attack masterminded by the Chief of Staff (later Field Marshal) Leonhard Graf von Blumenthal.

The allied Prussians and Austrians could continue the war without any problems, so they had to transfer troops from the conquered Jutland to the Danish islands.

The Danes had built a network of trenches and artillery positions along the entire coast from Sønderborg in the south to the tip of the Kær Peninsula Arnkilsøre in the north.

In the waters around Als, Danish warships and gunboats circled ready to intervene in the event of an attack on the island.

According to this, the Manstein Division was first to be put over and take possession of Arnkil, Rønhave, and the surrounding terrain; later it was to advance towards Ulkebøl and Hørup to prevent the Danish troops from embarking.

The Prussian command gave orders for the crossing of the Alssund – the narrow strait separating Als from the mainland of Jutland – to begin in the night of 28–29 June 1864.

The Commander-in-Chief had selected Øster Snogbæk, at the northern end of the strait, as the crossing place, the nearby Sottrup Storskov woods providing cover which enabled the preparations to be hidden from the Danes.

The Danish modern armoured monitor Rolf Krake was in Augustenborg fjord, and sailed to the Alssund where it caused the Prussians severe difficulties and stopped the crossing.