The February 1940 Altmark incident provides the campaign's political starting point. HMS Cossack pursued the German auxiliary into Jøssingfjord to free British sailors captured by Admiral Graf Spee, after Norwegian authorities had allowed Altmark to travel south through their waters. A Norwegian search in Britain's interest risked German retaliation, while refusing a search made Norway appear to favour Germany. Hitler later used the incident as anti-British propaganda, turning a dispute inside a fjord into evidence for German claims against Britain. Norway's effort to preserve neutrality had trapped it between two belligerent naval powers.
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The Altmark incident and neutrality under pressure
The Altmark incident shows how neutral Norway could satisfy neither Britain's demand to free captured sailors nor Germany's demand that the support ship continue through Norwegian waters.