Skagerrak is a gulf of the North Sea, bounded by Norway, Sweden and Denmark. Kattegat is the extension of Skagerrak to the Baltic Sea via Öresund.

In both world wars the Skagerrak was strategically very important for Germany. In the first World War, one of the biggest Sea Battles, the Battle of Skagerrak took place there. And its importance was one of the reasons to invade Denmark and Norway during WWII.