Unidentified structure at RAF Chipping Warden

While walking around the site of RAF Chipping Warden I have come across the remains of a structure I cannot identify. It is constructed in brick with concrete rendering in the top and sides. It only stand approximately 3 feet high and the circle in the top is approximately 10 feet across. Inside the are a couple of what I assume would have been small storage area that may at one time had doors on.
It is located close to the perimeter track close to the site of some former buildings and also the battle HQ.
I would guess it may have been some form of machine gun post or perhaps to site an AA gun but one of your members may be able to enlighten me.
I have taken some pictures although it is pretty overgrown.

This looks very similar to the "mystery structure" we discussed back in 07 April 2017 on the Bicester perimeter.