After about a year of preparation, on 4 June, German Admiral Karl Rudolf Brommy left Bremerhaven with the steam frigate SMS Barbarossa (formerly RMS Britannia) and the smaller steam corvettes Lübeck (1844) and Hamburg (1841) in order to disperse the Danish ships which were guarding the mouth of Weser River. The Danish forces present that day were inferior and retreated, but Brommy managed to cut off the sailing corvette Valkyrien which under captain Andreas Polder sought refuge near the island of Heligoland which at the time belonged to United Kingdom. The British, while being neutral, had anyway made clear beforehand that a German Navy was not welcome and might be treated as pirates.