 From there, they passed through the Dardanelles and Bosporus into the Black Sea to patrol the Danube, but they remained there only briefly before receiving orders to return home on 3 December owing to the rise in tensions between Denmark and the German states.Boiler problems aboard "Preussischer Adler", coupled with heavy coal usage, slowed the voyage back to Prussia, and they had only reached Brest, France by 3 February 1864, by which time war had again broken out between Denmark and the German Confederation.The Second Schleswig War had resulted from Denmark's November Constitution, passed in 1863, which integrated the duchies of Schleswig, Holstein, and Lauenburg with Denmark, a violation of the London Protocol that had ended the First Schleswig War.