Interesting BoB photo

[first-things-first]

We must have been at the same signings.

I have assumed that the firing butts were the brick walls with the supports. I have seen pictures of a similar structure near to one of the hangars (probably the tit lake one you mentioned).

Not sure what people meant by an underground base? There are some underground control rooms near to where the guard house was - all filled in with bits of concrete when we were kids.