▁Wes er üb ung , ▁but ▁were ▁not ▁fit ▁for ▁service ▁( e ither ▁due ▁to ▁damage , ▁command ▁changes ▁or ▁other ▁reasons ) ▁during ▁the ▁beginning ▁of ▁Hart mut . ▁These ▁sub mar ines ▁generally ▁operated ▁in ▁the ▁area ▁of ▁the ▁Or k ney ▁islands , ▁Sh et land ▁Islands , ▁and ▁near ▁Ber gen . ▁ ▁U - 1 7 ▁- ▁a ▁Type ▁II B ▁for ▁front line ▁training ; ▁until ▁late ▁April ▁U - 1 7 ▁was ▁not ▁on ▁war ▁pat rol . ▁ ▁U - 2 3 ▁- ▁Otto ▁K ret sch mer ' s ▁former ▁Type ▁II B . ▁The ▁sub marine ▁had ▁no ▁success ▁during ▁Hart mut . ▁ ▁U - 2 4 ▁- ▁a ▁Type ▁II B ▁that ▁began ▁operations ▁in ▁late ▁April ▁without ▁success . ▁ ▁U - 6 1 ▁- ▁a ▁Type ▁II C ▁under ▁the ▁command ▁of ▁J ürgen ▁O esten ▁went ▁on ▁pat rol ▁in ▁mid - A pril , ▁but ▁did ▁not ▁have ▁any ▁success . ▁ ▁Other ▁sub marine ▁actions ▁ ▁U - 2 6 ▁- ▁a ▁Type ▁I A ▁- ▁one ▁of ▁only ▁two ▁in ▁the ▁Kriegs marine ▁( the ▁other ▁being ▁U - 2 5 ▁from ▁Group ▁One ). ▁U - 2 6 ▁delivered ▁supplies ▁to ▁German ▁troops ▁in ▁Tr ond heim , ▁before ▁going ▁on ▁pat rol ▁and ▁s inking ▁one ▁British ▁supply ▁ship ▁on ▁ 2 1 ▁April . ▁ ▁U - 2 9 ▁- ▁a ▁Type ▁VII A ▁also ▁task ed ▁with ▁deliver ing ▁supplies