The Battle of Hegra Fortress was a 25-day engagement in the Norwegian Campaign which saw a small force of Norwegian volunteers fighting numerically superior German forces from a fortified position. After initial fighting around the Meråker Line railway line, the Norwegians pulled back into Hegra Fortress and held off further German attacks before surrendering on May 5 as one of the last Norwegian units active in southern Norway.
Here’s the American perspective of the situation in Norway.