I'm without dictionary at the moment, alas.

Stützpunkt in this context is most likely 'base', as Joe had it.

'Stollen' here is nothing to eat.
It also here is not what footballers have below their shoes to prevent slipping.
It is (oh, my memory):

I'll describe it to you: in mining, it is an underground man-made tunnel going parallel to earth surface.

In military context, it is any tunnel going roughly parallel to the earth, but it has to be fully below the earth, otherwise it would be 'Graben'.

Base:tunnel (if tunnel is the right word in military context) is the translation, but I don't know what that actually meqans in that context.

Wolfgang