▁captured ▁from ▁ ▁on ▁ 9 ▁May ▁ 1 9 4 1 . ▁In ▁August ▁ 1 9 4 1 , ▁D ön itz ▁began ▁address ing ▁U - bo ats ▁by ▁the ▁names ▁of ▁their ▁command ers , ▁instead ▁of ▁boat ▁numbers . ▁The ▁method ▁of ▁defining ▁U - bo at ▁meeting ▁points ▁in ▁the ▁Short ▁Sign al ▁Book ▁was ▁regarded ▁as ▁comprom ised , ▁so ▁a ▁method ▁was ▁defined ▁by ▁B - D ienst ▁crypt anal yst s ▁to ▁dis gu ise ▁their ▁positions ▁on ▁the ▁Kriegs marine ▁German ▁Naval ▁Grid ▁System ▁( G erman : Grad net z mel de ver fahren ) ▁was ▁introduced ▁and ▁used ▁until ▁the ▁end ▁of ▁the ▁war ▁ ▁Radio ▁direction ▁finding ▁A ware ▁of ▁the ▁danger ▁presented ▁by ▁radio ▁direction ▁finding ▁( R DF ), ▁the ▁Kriegs marine ▁developed ▁various ▁systems ▁to ▁speed ▁up ▁broadcast . ▁The ▁Kurz sign ale ▁code ▁system ▁cond ensed ▁messages ▁into ▁short ▁codes ▁consisting ▁of ▁short ▁sequences ▁for ▁common ▁terms ▁such ▁as ▁" con voy ▁location " ▁so ▁that ▁additional ▁descri ptions ▁would ▁not ▁be ▁needed ▁in ▁the ▁message . ▁The ▁resulting ▁Kurz signal ▁was ▁then ▁encoded ▁with ▁the ▁En igma ▁machine ▁and ▁subsequently ▁transm itted ▁as ▁rapidly ▁as ▁possible , ▁typically ▁taking ▁about ▁ 2 0 ▁seconds . ▁Typ ical ▁length ▁of ▁an ▁information ▁or ▁weather ▁signal ▁was ▁about ▁ 2 5 ▁characters . ▁ ▁Con vent ional ▁R DF ▁needed ▁about ▁a ▁minute ▁to ▁fix ▁the ▁bearing ▁of ▁a ▁radio ▁signal , ▁and ▁the ▁Kurz sign ale