I dont know about the use as a shelter, but you might be interested in the fact that one of the largest german shipyards Blohm & Voss is right at the south side

I dont know about the use as a shelter, but you might be interested in the fact that one of the largest german shipyards Blohm & Voss is right at the south side of the tunnel. [1] - https://en.wikipedia.org/wiki/Blohm%2BVoss https://en.wikipedia.org/wiki/Blohm%2BVoss