▁Kaiser lichen ▁Marine ),   ⁠ us eless ▁for ▁dec oding ▁the ▁Z imm ermann ▁Tele gram ▁but ▁valuable ▁when ▁it ▁came ▁to ▁dec oding ▁naval ▁traffic , ▁which ▁had ▁been ▁retrieved ▁from ▁the ▁w reck ed ▁cru iser ▁S MS ▁Mag de burg ▁by ▁the ▁Rus si ans , ▁who ▁passed ▁it ▁to ▁the ▁British . ▁▁ ▁Dis closure ▁of ▁the ▁tele gram ▁would ▁s way ▁public ▁opinion ▁in ▁the ▁United ▁States ▁against ▁Germany ▁if ▁the ▁British ▁could ▁conv ince ▁the ▁Americans ▁that ▁the ▁text ▁was ▁genu ine , ▁but ▁Room ▁ 4 0 ▁chief ▁William ▁Regin ald ▁Hall ▁was ▁rel uct ant ▁to ▁let ▁it ▁out ▁because ▁the ▁dis closure ▁would ▁expose ▁the ▁German ▁codes ▁broken ▁in ▁Room ▁ 4 0 ▁and ▁British ▁e aves dro pping ▁on ▁the ▁United ▁States ▁cable . ▁Hall ▁waited ▁three ▁weeks . ▁During ▁this ▁period , ▁de ▁Grey ▁and ▁crypt ograph er ▁William ▁Mont gom ery ▁completed ▁the ▁dec ryption . ▁On ▁ 1 ▁February ▁Germany ▁announced ▁res umption ▁of ▁" un rest rict ed " ▁sub marine ▁war fare , ▁an ▁act ▁which ▁led ▁the ▁United ▁States ▁to ▁break ▁off ▁diplom atic ▁relations ▁with ▁Germany ▁on ▁ 3 ▁February . ▁ ▁Hall ▁passed ▁the ▁tele gram ▁to ▁the ▁British ▁Foreign ▁Office ▁on ▁ 5 ▁February , ▁but ▁still ▁war ned ▁against ▁re le asing ▁it . ▁Meanwhile , ▁the ▁British ▁discussed ▁possible ▁cover ▁stories ▁which ▁would ▁serve ▁to ▁explain ▁to ▁the ▁Americans ▁how ▁they ▁obtained ▁the ▁c oded ▁text ▁of ▁the ▁tele gram ▁without