, ▁then ▁transferred ▁to ▁the ▁ 3 rd ▁U - bo at ▁Fl ot illa ▁for ▁oper ational ▁service . ▁ ▁She ▁was ▁s unk ▁by ▁Al lied ▁war ships ▁in ▁mid - At l antic ▁in ▁February ▁ 1 9 4 4 . ▁ ▁Design ▁German ▁Type ▁VII C ▁sub mar ines ▁were ▁preced ed ▁by ▁the ▁shorter ▁Type ▁VII B ▁sub mar ines . ▁U - 2 5 7 ▁had ▁a ▁disp lacement ▁of ▁ ▁when ▁at ▁the ▁surface ▁and ▁ ▁while ▁sub mer ged . ▁She ▁had ▁a ▁total ▁length ▁of ▁, ▁a ▁pressure ▁h ull ▁length ▁of ▁, ▁a ▁beam ▁of ▁, ▁a ▁height ▁of ▁, ▁and ▁a ▁dra ug ht ▁of ▁. ▁The ▁sub marine ▁was ▁power ed ▁by ▁two ▁Germania wer ft ▁F 4 6 ▁four - stroke , ▁six - cy l inder ▁super charg ed ▁dies el ▁engines ▁producing ▁a ▁total ▁of ▁ ▁for ▁use ▁while ▁sur fac ed , ▁two ▁A EG ▁G U ▁ 4 6 0 / 8 – 2 7 ▁double - act ing ▁electric ▁mot ors ▁producing ▁a ▁total ▁of ▁ ▁for ▁use ▁while ▁sub mer ged . ▁She ▁had ▁two ▁sh aft s ▁and ▁two ▁ ▁prop ellers . ▁The ▁boat ▁was ▁capable ▁of ▁operating ▁at ▁depth s ▁of ▁up ▁to ▁. ▁ ▁The ▁sub marine ▁had ▁a ▁maximum ▁surface ▁speed ▁of ▁ ▁and ▁a ▁maximum ▁sub mer ged ▁speed ▁of ▁. ▁When ▁sub mer ged , ▁the ▁boat ▁could ▁operate ▁for ▁ ▁at ▁; ▁when ▁sur fac ed