. ▁ ▁Due ▁to ▁sub mar ines ' ▁generally ▁slow ▁surface ▁speed ▁compared ▁to ▁surface ▁vessels , ▁many ▁of ▁the ▁U - bo ats ▁specifically ▁assigned ▁to ▁perform ▁in ▁Operation ▁Wes er üb ung ▁depart ed ▁before ▁the ▁main ▁surface ▁fleet ▁left ▁from ▁the ▁mouth ▁of ▁the ▁Wes er ▁river ▁on ▁the ▁morning ▁of ▁ 7 ▁April . ▁Tw enty ▁U - bo ats ▁went ▁out ▁on ▁ 3 , ▁ 4 ▁and ▁ 5 ▁April . ▁ ▁Hart mut ▁prepar ations ▁Pre par ations ▁in ▁the ▁German ▁sub marine ▁forces ▁( U - boot wa ffe ) ▁began ▁in ▁early ▁March . ▁On ▁ 4 ▁March ▁ 1 9 4 0 ▁Karl ▁D ön itz ▁received ▁orders ▁from ▁his ▁super iors ▁in ▁Berlin : ▁▁ ▁Further ▁U - bo at ▁sail ings ▁are ▁to ▁be ▁stopped . ▁ ▁U - bo ats ▁which ▁have ▁already ▁sa iled ▁are ▁not ▁to ▁operate ▁off ▁the ▁Norwegian ▁coast . ▁ ▁All ▁Naval ▁forces ▁to ▁be ▁ready ▁for ▁operations ▁as ▁quickly ▁as ▁possible . ▁ ▁No ▁special ▁degree ▁of ▁read iness . ▁ ▁D ön itz ▁mobil ized ▁any ▁vessel ▁that ▁could ▁d ive . ▁Only ▁ 1 2 ▁larger ▁Type ▁VII ▁and ▁Type ▁IX ▁sub mar ines ▁capable ▁of ▁operating ▁in ▁the ▁Atlantic ▁Ocean ▁were ▁fit ▁for ▁the ▁operation . ▁One ▁older ▁ocean - going ▁Type ▁I A ▁was ▁also ▁included . ▁ 1 2 ▁smaller ▁ ▁Type ▁II ▁U - bo ats ▁were ▁called ▁up , ▁despite ▁that ▁the ▁Norwegian ▁coast ▁limited ▁their ▁operating