Can some one please explain?

I just watched this production last night, and certainly one of its flaws was that the dialogue-- such as there was of it-- was frequently incomprehensible. Even rewinding and relistening often didn't help. As such, there were times when I was left with no idea whatsoever of what was going on. This was especially true in the tunnels.

Just what *were* they doing in the tunnels? I thought I heard snippets in the dialogue that suggested they were planting mines or something, but I saw no evidence of this in the actual scenes in the tunnels. All I saw was an inexplicably large number of men standing around while one guy listened for something. Then he would hear something bad, and they would all scamper to get out. But since *none* of the others were actually *doing* anything, it was hard to understand why they were there in the first place. It just made it harder to get them all out when there was trouble. Plus all those extra guys were using up the available air. (and were we really expected to believe that that that large array of tunnels were sufficiently aired by that one silly hand-pump?)

Seriously, what were *all* those guys doing in the tunnel? Why was it *so* important to have lots of guys in the tunnel that they were stealing men from the infantry? Why, in particular, was it so important to have an infantry *lieutenant* go down in the tunnel? I could make out none of the dialogue around that.