History of the North Sea the North Sea though they saw little action. The Austro-Prussian War (1866) resulted in Prussia's gaining full control of the Kiel Canal, allowing their Baltic ports access to the North Sea. France declared war on Prussia 19 July 1870 which initiated the Franco-Prussian War (1870–1871). The French Navy was, at the time far larger and superior to the North German Federal Navy, the Navy of the North German Confederation. Though the French did take a number of merchant ships bound to and from North Germany, shortages of manpower and coal, as well as conflicting orders, made the attempted blockade of
Kiel Canal Navy, between 1907 and 1914 the canal width was increased. The widening of the canal allowed the passage of a "Dreadnought"-sized battleship. This meant that these battleships could travel from the Baltic Sea to the North Sea without having to go around Denmark. The enlargement projects were completed by the installation of two larger canal locks in Brunsbüttel and Holtenau. 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. (The United States opposed this proposal