▁approximately ▁ ▁north - east ▁of ▁Sydney ▁He ads , ▁with ▁all ▁five ▁sub mar ines ▁in ▁position ▁by ▁ 2 9 ▁May . ▁ ▁M idget ▁sub marine ▁operation ▁ ▁Final ▁reconna issance ▁Before ▁dawn ▁on ▁ 2 9 ▁May , ▁I - 2 1 s ▁float plane , ▁pil oted ▁by ▁I to ▁Sus um u , ▁performed ▁a ▁final ▁reconna issance ▁flight ▁over ▁Sydney ▁Har bour , ▁with ▁the ▁mission ▁of ▁mapping ▁the ▁locations ▁of ▁the ▁major ▁vessels ▁and ▁of ▁the ▁anti - sub marine ▁net . ▁Multiple ▁obser vers ▁sp otted ▁the ▁float plane ▁but ▁assumed ▁it ▁was ▁a ▁US ▁Navy ▁Curt iss ▁Se ag ull . ▁No ▁alarm ▁was ▁raised ▁until ▁ 0 5 : 0 7 , ▁when ▁it ▁was ▁real ised ▁that ▁the ▁only ▁ship ▁in ▁the ▁area ▁carrying ▁Se ag ull s ▁was ▁the ▁U . S . ▁cru iser ▁Chicago , ▁and ▁all ▁four ▁of ▁her ▁aircraft ▁were ▁on ▁board . ▁Richmond ▁Air ▁Force ▁Base ▁launched ▁RA AF ▁Wir ra way ▁f igh ters , ▁which ▁failed ▁to ▁locate ▁I - 2 1 ▁or ▁the ▁float plane . ▁Therefore , ▁the ▁reconna issance ▁flight ▁did ▁not ▁result ▁in ▁the ▁authorities ▁in ▁Sydney ▁taking ▁any ▁special ▁defence ▁measures . ▁The ▁float plane ▁was ▁seriously ▁dam aged ▁on ▁landing ▁and ▁had ▁to ▁be ▁sc utt led , ▁but ▁both ▁air cre w ▁surv ived . ▁ ▁Plan ▁of ▁attack ▁The ▁Japanese ▁planned ▁to ▁launch ▁the ▁m idget s ▁one ▁after ▁the ▁other ▁between ▁ 1 7