Narvik, in northern Norway, being ice-free all year round, is the main port for shipment of iron ore from the Swedish mines in Kiruna. Access to high-quality iron ore was crucial to Germany's war effort and one of Hitler's primary objectives in the invasion of Norway in April 1940 was therefore to secure Narvik. The allies were naturally anxious to prevent this and the result was two major naval battles, the First and Second Battle of Narvik, on 9-10 and 13 April 1940 respectively. You can read an abbreviated version of the whole story here: http://www.immersed.com/Articles/narvik__norway.htm
Today, Narvik is a mecca for wreck divers as the wrecks are almost all within sports diving limits and the visibility is excellent, 10 metres at worst and 25-30 metres at best when I was there. The wrecks are still well preserved after more than 60 years and are covered with life.