http://en.wikipedia.org/wiki/Brisbane_Line
I'd read of this before and seen the tank traps at tenterfield , last week
went for a paddle and fish at paddys flat and theres more of them .
There is a fair bit of angst around the whole time back then and what the powers that be had planned ,its hard to ignore a lot of trouble was went to to build these fortifications without a lot of records intact in regard.