In late 1863, tensions began to increase between the German Confederation and Denmark over the latter's November Constitution, which integrated the duchies of Schleswig, Holstein, and Lauenburg with Denmark, a violation of the London Protocol that had ended the First Schleswig War. The crisis erupted in the Second Schleswig War, which began on 1 February 1864, after the Prussian and Austrian Empires delivered an ultimatum to Denmark to cede the disputed duchies to Austro-Prussian control. At the time, the Danish fleet was far superior to the Prussian naval forces initially available, which allowed the Danes to blockade the German coast. The bulk of the Prussian fleet was concentrated in the Baltic Sea, and the Austrian fleet was primarily stationed in the Mediterranean Sea. Also in the Mediterranean were the Prussian aviso and the gunboats and ; these vessels were immediately recalled to German waters.