▁damage ▁when ▁the ▁same ▁destroy ers ▁depth ▁charged ▁her . ▁ ▁Operation ▁Results ▁U - bo ats ▁succeeded ▁in ▁reporting ▁some ▁Al lied ▁fleet ▁movements , ▁but ▁D ön itz ' ▁greatest ▁interest ▁was ▁s inking ▁ships ▁- ▁a ▁portion ▁of ▁Hart mut ▁where ▁the ▁U - bo ats ▁performed ▁under wh el ming ly . ▁In ▁general , ▁sub marine ▁attacks ▁in ▁the ▁Norwegian ▁waters ▁proved ▁in effect ive . ▁Near ly ▁two - third s ▁of ▁the ▁magnetic ▁p ist ols ▁failed ▁by ▁either ▁det on ating ▁too ▁early , ▁not ▁ar ming , ▁or ▁running ▁too ▁deep . ▁ ▁Despite ▁orders ▁to ▁ce ase ▁using ▁magnetic ▁p ist ols ▁in ▁late ▁ 1 9 3 9 , ▁D ön itz ▁had ▁author ized ▁command ers ▁to ▁use ▁either ▁magnetic ▁or ▁impact ▁p ist ols ▁on ▁their ▁tor ped o es ▁during ▁Operation ▁Wes er üb ung . ▁Cold ▁water ▁in ▁the ▁North ▁Sea ▁and ▁Norwegian ▁f j ords ▁ham per ed ▁the ▁use ▁of ▁electric ▁tor ped o es ▁used ▁at ▁the ▁time , ▁which ▁required ▁he ating ▁to ▁reach ▁suitable ▁operating ▁temperature . ▁ ▁Other ▁spec ulation ▁has ▁pointed ▁to ▁the ▁un famil iar ▁conditions ▁of ▁the ▁campaign ▁for ▁the ▁ab norm ally ▁large ▁number ▁of ▁tor ped o ▁fail ures . ▁Most ▁command ers ▁were ▁used ▁to ▁operating ▁at ▁sea ▁where ▁the ▁effect ▁of ▁t ides ▁and ▁curr ents ▁over ▁short ▁distances ▁is ▁neg lig ible ▁between ▁a ▁boat ▁and ▁its ▁target . ▁Under water ▁movement ▁may ▁have