Sergeant James Hall III, among about 1,300 service personnel stationed at Teufelsberg, was granted the highest security clearance for access to sensitive compartmental information. The U.S. Field Station Teufelsberg (literally: Devil's Mountain) was a highly-sensitive installation atop a high hill, which was formed from rubble of buildings in the city destroyed during World War II by Allied airstrikes and Soviet artillery. Thanks to its elevation, the location in an otherwise flat landscape was ideal for monitoring military and civilian communications originating from East Germany and other Iron Curtain countries.