3 1 ▁May ▁– ▁ 1 ▁June , ▁three ▁Ko - hy ote ki - class ▁m idget ▁sub mar ines , ▁each ▁with ▁a ▁two - member ▁crew , ▁entered ▁Sydney ▁Har bour , ▁avoided ▁the ▁partially ▁constructed ▁Sydney ▁Har bour ▁anti - sub marine ▁bo om ▁net , ▁and ▁attempted ▁to ▁sink ▁Al lied ▁war ships . ▁Two ▁of ▁the ▁m idget ▁sub mar ines ▁were ▁detected ▁and ▁attacked ▁before ▁they ▁could ▁successfully ▁eng age ▁any ▁Al lied ▁vessels , ▁and ▁the ▁cre ws ▁sc utt led ▁their ▁sub mar ines ▁and ▁killed ▁themselves . ▁These ▁sub mar ines ▁were ▁later ▁recovered ▁by ▁the ▁Al lies . ▁The ▁third ▁sub marine ▁attempted ▁to ▁tor ped o ▁the ▁heavy ▁cru iser ▁, ▁but ▁instead ▁s ank ▁the ▁converted ▁fer ry ▁, ▁killing ▁ 2 1 ▁sail ors . ▁This ▁m idget ▁sub marine ' s ▁fate ▁was ▁unknown ▁until ▁ 2 0 0 6 , ▁when ▁amateur ▁sc uba ▁divers ▁discovered ▁the ▁w reck ▁off ▁Sydney ' s ▁northern ▁be aches . ▁ ▁Im medi ately ▁following ▁the ▁ra id , ▁the ▁five ▁Japanese ▁fleet ▁sub mar ines ▁that ▁carried ▁the ▁m idget ▁sub mar ines ▁to ▁Australia ▁emb ark ed ▁on ▁a ▁campaign ▁to ▁dis rupt ▁merchant ▁sh ipping ▁in ▁eastern ▁Australian ▁waters . ▁Over ▁the ▁next ▁month , ▁the ▁sub mar ines ▁attacked ▁at ▁least ▁seven ▁merchant ▁vessels , ▁s inking ▁three ▁ships ▁and ▁killing ▁ 5 0 ▁sail ors . ▁During ▁this ▁period , ▁between ▁mid night ▁and ▁