concrete block:- (#16 on the layout
At first glance it apears
to be a anti tank obstacle. its basic dimensions are as follows
Top: 48" X 53"
Base: 72" X 72"
the top you can make out where a circular mounting ring was placed,
this was probably used to crane this heavy block into place.
There are also two large notches on the right and left side of
the block. Obviously something was mounted on this block, but
what? Perhaps powerfull naval binoculars? The officer quarters
are just above this site.