▁be ▁laid ▁beneath ▁enemy ▁ships , ▁but ▁it ▁was ▁marked ly ▁smaller ▁and ▁had ▁substantial ▁differences ▁from ▁the ▁X ▁class . ▁It ▁disp ensed ▁with ▁a ▁dual ▁dies el / elect ric ▁prop ulsion ▁system , ▁re lying ▁instead ▁sole ly ▁on ▁elect rical ▁power ▁in ▁the ▁form ▁of ▁a ▁ 1 2   hp ▁A EG ▁tor ped o ▁motor , ▁on ▁the ▁basis ▁that ▁since ▁it ▁would ▁operate ▁sub mer ged ▁there ▁was ▁no ▁need ▁for ▁a ▁dies el ▁engine . ▁However , ▁this ▁resulted ▁in ▁a ▁very ▁low ▁end urance ▁of ▁ ▁at ▁. ▁ ▁Since ▁the ▁boat ▁would ▁need ▁to ▁be ▁able ▁to ▁pass ▁through ▁anti - sub marine ▁n ets ▁and ▁similar ▁obst acles , ▁it ▁was ▁designed ▁without ▁hydro plan es ▁or ▁fins , ▁her ▁trim ▁being ▁controlled ▁with ▁adjust able ▁weights ▁within ▁the ▁pressure ▁h ull . ▁In ▁practice ▁this ▁proved ▁totally ▁in effect ive ▁since ▁the ▁weights ▁could ▁not ▁be ▁moved ▁quickly ▁enough ▁and ▁hydro plan es ▁and ▁fins ▁were ▁subsequently ▁fitted . ▁Sub mer ged ▁control ▁was ▁still ▁poor , ▁since ▁He cht ▁was ▁not ▁fitted ▁with ▁ball ast ▁t anks . ▁ ▁Even ▁though ▁He cht ▁had ▁been ▁designed ▁to ▁transport ▁an ▁explos ive ▁charge , ▁Karl ▁D ön itz ▁ins isted ▁that ▁a ▁tor ped o ▁be ▁carried ▁so ▁that ▁attacks ▁could ▁be ▁carried ▁out ▁on ▁vessels ▁in ▁coast al ▁waters ▁and ▁He cht ▁was ▁designed ▁to ▁be ▁armed ▁either ▁with ▁an ▁unders lung ▁tor ped o ▁or ▁an ▁unders lung ▁mine