unn elling ▁shield s ▁as ▁being ▁the ▁pat ented ▁but ▁un im plement ed ▁idea ▁of ▁Bar low ' s ▁in ▁ 1 8 6 4 ▁but ▁the ▁actual ▁construction ▁of ▁a ▁different ▁pat ented ▁device ▁by ▁Great head ▁was ▁built ▁and ▁first ▁used ▁on ▁the ▁Tower ▁Sub way ▁and ▁simultaneously ▁in ▁New ▁York , ▁Beach ▁created ▁and ▁made ▁his ▁own ▁shield ▁independently ▁of ▁Bar low ' s ▁and ▁Great head ' s ▁designs . ▁Bar low ▁lost ▁out ▁on ▁credit ▁because ▁he ▁never ▁actually ▁constructed ▁one , ▁only ▁pat ent ing ▁the ▁idea . ▁Co pper th wa ite ▁also ▁reve als ▁that ▁Great head ▁was ▁una ware ▁of ▁the ▁ 1 8 6 8 ▁prov is ional ▁pat ent ▁of ▁Bar low ' s ▁until ▁ 1 8 9 5 , ▁a ▁fact ▁discussed ▁in ▁an ▁ 1 8 9 5 ▁Institution ▁of ▁Civil ▁Engine ers ▁paper ▁on ▁the ▁City ▁and ▁South ▁London ▁Railway ▁acknowled ged ▁by ▁Bar low . ▁ ▁A ▁tunnel ▁ ▁long ▁was ▁d ug ▁with ▁a ▁diameter ▁of ▁, ▁a ▁maximum ▁of ▁ ▁below ▁the ▁high - water ▁level . ▁This ▁was ▁b ored ▁through ▁a ▁stable ▁layer ▁of ▁the ▁London ▁cl ay ▁that ▁lay ▁ ▁below ▁the ▁river ▁bed , ▁below ▁the ▁soft ▁all uv ial ▁depos its ▁that ▁had ▁pl ag ued ▁the ▁construction ▁by ▁Brun el ▁of ▁the ▁earlier ▁Th ames ▁T unnel . ▁This , ▁combined ▁with ▁the ▁simpler ▁nature ▁of ▁the ▁project   – ▁the ▁exc av ation ▁face ▁was ▁only ▁one