After 1864 Second Schleswig War put Schleswig-Holstein under the government of Prussia (from 1871 the German Empire), a new canal was sought by merchants and by the German navy, which wanted to link its bases in the Baltic and the North Sea without the need to sail around Denmark [REF].
After World War I, the Treaty of Versailles required the canal to be open to vessels of commerce and of war of any nation at peace with Germany, while leaving it under German administration [REF].