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 Belt, the Little Belt and The Sound ("Öresund"/"Øresund"), connect the Baltic Sea with the Kattegat and Skagerrak strait in the North Sea. The water temperature of the Baltic Sea varies significantly depending on exact location, season and depth. At the Bornholm Basin, which is located directly east of the island of the same name, the surface temperature typically falls to during the peak of the winter and rises to during the peak of the summer, with an annual average of around . A similar pattern can be seen in the Gotland Basin, which is located between the island of Gotland