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
Baltic Sea in addition to coastal fringes in more southerly locations such as the Gulf of Riga. This description meant that the whole of the Baltic Sea was covered with ice. Since 1720, the Baltic Sea has frozen over entirely 20 times, most recently in early 1987, which was the most severe winter in Scandinavia since 1720. The ice then covered . During the winter of 2010–11, which was quite severe compared to those of the last decades, the maximum ice cover was , which was reached on 25 February 2011. The ice then extended from the north down to the northern