▁worked ▁under ▁Great head , ▁both ▁Great head ▁in ▁England ▁and ▁Alfred ▁E ly ▁Beach ▁in ▁New ▁York ▁invent ed ▁and ▁constructed ▁their ▁own ▁versions ▁of ▁t unn elling ▁shield s ▁simultaneously ▁and ▁independently ▁of ▁each ▁other . ▁ ▁Work ▁began ▁in ▁February ▁ 1 8 6 9 ▁with ▁the ▁b oring ▁of ▁entrance ▁sh aft s , ▁ ▁deep ▁on ▁the ▁north ▁bank ▁and ▁ ▁deep ▁on ▁the ▁south ▁bank . ▁The ▁t unn elling ▁itself ▁started ▁in ▁April ▁using ▁the ▁circular ▁ ▁Great head ▁shield . ▁ ▁Wh ilst ▁many ▁argue ▁that ▁the ▁shield ▁used ▁was ▁a ▁" Bar low – Gre at head " ▁shield , ▁William ▁Co pper th wa ite ▁says ▁"... ▁in ▁ 1 8 6 8 ▁[ Bar low ] ▁provision ally ▁pat ented ▁a ▁shield ▁having ▁near ▁the ▁cutting ▁edge ▁a ▁trans verse ▁partition ▁or ▁dia ph rag m . ▁Ne ither ▁of ▁these ▁designs ▁took ▁practical ▁form , ▁and ▁in ▁ 1 8 6 9 ▁Great head ▁in ▁England ▁and ▁Beach ▁in ▁New ▁York ▁actually ▁built ▁and ▁used ▁shield s ▁having ▁many ▁features ▁in ▁common ▁with ▁Bar low ' s ▁pat ents ▁but ▁differ ing ▁from ▁each ▁other ▁in ▁details ... ▁Beach ' s ▁shield ▁res emble d ▁Bar low ' s ▁pat ent ▁of ▁ 1 8 6 4 , ▁and ▁Great head ' s ▁the ▁prov is ional ▁pat ent ▁of ▁ 1 8 6 8 ." ▁Co pper th wa ite ▁puts ▁to ▁bed ▁all ▁arguments ▁over ▁orig ins ▁of ▁t