▁Navy ▁General ▁Staff ▁only ▁after ▁much ▁cont ention ▁with ▁Naval ▁Head quarters , ▁including ▁a ▁threat ▁to ▁res ign ▁his ▁command . ▁Full - scale ▁planning ▁was ▁under way ▁by ▁early ▁spring ▁ 1 9 4 1 , ▁primarily ▁by ▁R ear ▁Admir al ▁Ry ū nos u ke ▁K us aka , ▁with ▁assistance ▁from ▁Captain ▁Minor u ▁G enda ▁and ▁Yam am oto ' s ▁Deput y ▁Chief ▁of ▁Staff , ▁Captain ▁Kam eto ▁K uro sh ima . ▁The ▁pl ann ers ▁studied ▁the ▁ 1 9 4 0 ▁British ▁air ▁attack ▁on ▁the ▁Italian ▁fleet ▁at ▁Tar anto ▁intens ively . ▁ ▁Over ▁the ▁next ▁several ▁months , ▁pil ots ▁were ▁trained , ▁equipment ▁was ▁adapted , ▁and ▁intelligence ▁was ▁collected . ▁Despite ▁these ▁prepar ations , ▁Emperor ▁H iro h ito ▁did ▁not ▁appro ve ▁the ▁attack ▁plan ▁until ▁November ▁ 5 , ▁after ▁the ▁third ▁of ▁four ▁Imperial ▁Con ferences ▁called ▁to ▁consider ▁the ▁matter . ▁Final ▁authorization ▁was ▁not ▁given ▁by ▁the ▁em peror ▁until ▁December ▁ 1 , ▁after ▁a ▁majority ▁of ▁Japanese ▁leaders ▁ad vised ▁him ▁the ▁" H ull ▁Note " ▁would ▁" destroy ▁the ▁f ruits ▁of ▁the ▁China ▁incident , ▁end anger ▁Man ch u ku o ▁and ▁und erm ine ▁Japanese ▁control ▁of ▁Korea ." ▁ ▁By ▁late ▁ 1 9 4 1 , ▁many ▁obser vers ▁believed ▁that ▁host ilities ▁between ▁the ▁U . S . ▁and ▁Japan ▁were ▁im min ent . ▁A ▁Gall up ▁poll ▁just ▁before