Wartime remnants

Being the second highest hill in Dorset, Bulbarrow Hill has always been of military and strategic importance. The Iron Age peoples had a hillfort here, it was the site of an Armada warning beacon in the 1500's, during the Napoleonic Wars there was a telegraph station here, and during the Second World War and beyond the RAF had a radar station on the summit, RAF Bulbarrow. There are still radio transmitters active today, although the military have long gone. Much of the wartime equipment too has gone, leaving a handful of buildings where the masts were and the accommodation, Naafi and other ancillary buildings tucked away in an adjacent wood. These can be seen from the roadside, although I think I'd need to get permission to explore further, as they're now in private hands. Though whilst walking back along the ridge towards Okeford Fitzpaine, I spied something in the roadside undergrowth.  On inspection it was a rectangular (almost square) concrete feature, open ended (at both ends), with a series of deep recesses in the walls; I couldn't make out the floors construction due to soil deposition, although I imagine that too was concrete. The site looked to me to be an anti aircraft position, it exhibited several common features with anti aircraft I've visited before.  On my return home I checked online and found a guys wartime recollections of being station on Bulbarrow as part of a Bofors unit, so maybe. Further investigation of these sites and, no doubt, others on Bulbarrow is required.