in the woods

My Grandparents lived in Highmoor so I have passed this many time, it's the first time I have stopped and looked at it.
It's from the 2nd World War.

"In the woods near Nettlebed in England is a small reminder of the US Army Engineers' presence in the area in World War II. A small stone 'Castle', taken from the Engineer's badge, was said to be one of two constructed at the entrances to Nettlebed Camp. This was a camp used by US Engineers as a training base set in the woods of the Chilterns north of Reading and near Henley. On it is a sign saying 1942 - 343rd Engineers US Army, probably the unit which built the camp."