▁U - bo at ▁and ▁the ▁v ener able ▁U . S . ▁Navy ▁fleet ▁sub marine . ▁ ▁The ▁Tang - class ▁and ▁the ▁fleet ▁sub mar ines ▁converted ▁under ▁the ▁Gre ater ▁Under water ▁Prop ulsion ▁Power ▁( G UP PY ) ▁program ▁had ▁much ▁higher ▁sub mer ged ▁performance ▁than ▁their ▁prede cess ors , ▁but ▁were ▁quickly ▁sur pass ed ▁by ▁the ▁nuclear - prop elled ▁sub mar ines ▁that ▁entered ▁service ▁beginning ▁in ▁ 1 9 5 4 . ▁ ▁Design ▁Probably ▁the ▁most ▁important ▁innov ation ▁of ▁the ▁T angs , ▁and ▁their ▁primary ▁advantage ▁over ▁contemporary ▁G UP PY ▁convers ions , ▁was ▁an ▁increase ▁in ▁test ▁depth ▁from ▁ ▁to ▁, ▁achieved ▁with ▁H Y - 4 2 ▁( ▁yield ▁strength ) ▁steel . ▁The ▁improved ▁H Y - 7 5 ▁steel ▁would ▁not ▁appear ▁until ▁mid ▁ 1 9 5 0 s . ▁This ▁allowed ▁the ▁class ▁to ▁take ▁advantage ▁of ▁deeper ▁ocean ▁conditions ▁to ▁e va de ▁son ar , ▁as ▁well ▁as ▁man eu ver ▁more ▁safely ▁at ▁moder ate ▁depth s . ▁ ▁An ▁un success ful ▁innov ation ▁of ▁the ▁Tang ▁design ▁was ▁the ▁General ▁Mot ors ▁E MD ▁ 1 6 - 3 3 8 ▁light weight , ▁compact , ▁high - speed ▁" pan ca ke " ▁engine , ▁r ated ▁at ▁ 1 , 0 0 0 ▁b hp . ▁ ▁Very ▁different ▁from ▁the ▁classic ▁dies el ▁engines ▁that ▁nearly ▁all ▁preceding ▁sub mar ines ▁used