At first I thought this was a defensive pillbox on the perimeter of the old WWII RAF airfield at Chedworth, but a bit of Googling suggests its is a 'battle HQ' pillbox
from where the Station Commander would direct operations should the airfield be under attack. Apparently, although strictly you'd be trespassing you can gain
entry and go down a couple of levels. Amazing to think this and other old buildings from when this was an active RAF station during the war still survive, over 80 years ago