Playing war

When we were kids we used to play war (it's okay, it was the 70's and playing war was almost compulsory) in the humps and bumps and hollows which cover one of the west facing, pine covered, slopes of St Catherine's Hill. When we played here the hillside was covered with invasive Rhododendron, so we couldn't see how the humps, bumps and hollows we built our camps amongst were connected. I discovered many years later that, ironically, what we were playing war in, were in fact First World War training trenches, where men learnt the skills of trench warfare before entering the bloody fray. Eerily weird, thinking about that now. During the war years the hillside was fortified as it would have been on the Western Front, forward trenches, machine gun positions, command bunkers, dug outs, shafts and tunnels, communication trenches and rear trenches, everything. Now that the Rhododendrons have been cleared you can get an inkling of what parts of the hill may have looked like, you can definitely make out a section of classic 'zig zag' trench work, along with several larger positions. I got to thinking, how much evidence, if any, of the underground works survive? Or were all the works filled or collapsed? I wonder if any geophysical surveys have been undertaken.