t ens ile ▁steel ▁that ▁would ▁enable ▁it ▁to ▁surv ive ▁the ▁impact ▁before ▁det on ation . ▁At ▁the ▁same ▁time , ▁to ▁achieve ▁the ▁pen etr ation ▁required , ▁Wall is ▁designed ▁the ▁T all boy ▁to ▁be ▁very ▁aer od ynamic ▁so ▁that , ▁when ▁dropped ▁from ▁a ▁great ▁height , ▁it ▁would ▁reach ▁a ▁much ▁higher ▁terminal ▁velocity ▁than ▁traditional ▁bomb ▁designs . ▁ ▁In ▁the ▁final ▁design , ▁the ▁No . ▁ 7 8 ▁Mark ▁I ▁tail ▁of ▁the ▁bomb ▁was ▁about ▁half ▁the ▁overall ▁length ▁of ▁the ▁finished ▁weapon ; ▁the ▁bomb ▁cas ing ▁was ▁some ▁ ▁of ▁the ▁overall ▁ ▁length . ▁Initial ly , ▁the ▁bomb ▁had ▁a ▁t endency ▁to ▁t umble , ▁so ▁the ▁tail ▁was ▁modified : ▁the ▁fins ▁were ▁given ▁a ▁slight ▁tw ist ▁so ▁that ▁the ▁bomb ▁sp un ▁as ▁it ▁fell . ▁The ▁gy ro scop ic ▁effect ▁thus ▁generated ▁stopped ▁the ▁pitch ing ▁and ▁y aw ing , ▁impro ving ▁both ▁aer od ynam ics ▁and ▁accuracy . ▁ ▁T all boy ▁was ▁designed ▁to ▁be ▁dropped ▁from ▁an ▁optimal ▁alt itude ▁of ▁ ▁at ▁a ▁forward ▁speed ▁of ▁, ▁hitting ▁at ▁. ▁It ▁made ▁a ▁cr ater ▁ ▁deep ▁and ▁ ▁across ▁and ▁could ▁go ▁through ▁ ▁of ▁concrete . ▁ ▁The ▁weight ▁of ▁the ▁T all boy ▁( appro xim ately ▁) ▁and ▁the ▁high ▁alt itude ▁required ▁of ▁the ▁bomb ing ▁aircraft ▁meant ▁that ▁the ▁Av ro ▁Lanc aster s ▁used ▁had ▁to ▁be ▁spe