Visitors to Endcliffe Park, a small green space on the west side of the UK city of Sheffield, might come across a curious monument. It begins with a large, permanent American flag. Then, they'll notice several trees surrounding a large boulder. Flags representing the United States Air Force, small wooden crosses, and other tokens of appreciation flanking that boulder, which bears plaques and, often, ten photos of World War II-era airmen.  Those airmen, 1st Lt. John Kriegshauser, 2nd Lt. Lyle...