Basically three Milton, CPM, or Hanson concrete Manhole chamber rings, cut and adapted, and sat on what is called a ‘biscuit’ or a cover slab with one on top. all available from any reputable Civil engineering suppliers for about £100 a throw:)
It was for the forces, a cheap way of making a pillbox type position, at very little cost. We put loads of those in different airbases and installations all over the UK.
Now what did i tell you TT:D