English Heritage say:
A series of ammunition storage bunkers in Savernake Forest constructed during or shortly after WWII were seen as earthworks and mapped and interpreted from a combination of lidar derived imagery and aerial photographs as part of the Savernake Forest NMP project. The main information on the bunkers was recovered from the lidar derived imagery, but there are slight traces of what might be the initial works relating to the bunkers on the USAAF photographs from 1944. There are 14 bunkers in all, the majority aligned down the Grand Avenue with one outlier on Charcoal Burners Road. From the lidar derived imagery it looks as though the bulk of the bunkers follow the same pattern. They consist of a sub-rectangular mound against the road with a pen-annular bank curving round from the edges of the mound forming blast walls and leaving a flat area which would have been the location of the actual dump.
Mostly US use but was considered, in 1941, by the Air Ministry as an RAF Forward Ammunition Depot but never built.
The image on GE is the remains of a store on Charcoal Burner's Road