A notable event in Drøbak's history is the World War II sinking of the German cruiser "Blücher" in the Drøbak narrows (only 1 mile (1.5 km) wide), on the early morning of 9 April 1940. The cruiser was transporting German soldiers and bureaucrats for the planned swift occupation of Oslo, but the Battle of Drøbak Sound, resulting in the sinking by the Oscarsborg fortress delayed this, and thus allowed for the evacuation of the Norwegian Royal Family, parliament, and cabinet, and for the nation's gold reserves to be denied the occupiers.