acy ▁of ▁the ▁sub mar ines ' ▁range - find ing ▁equipment , ▁couple d ▁with ▁the ▁un stable ▁firing ▁platform ▁of ▁a ▁sub marine ▁at ▁sea , ▁specific ▁target ing ▁was ▁impossible . ▁The ▁intention ▁of ▁the ▁sub marine ▁bomb ard ment ▁was ▁to ▁fright en ▁the ▁population ▁of ▁the ▁target ▁area . ▁ ▁The ▁failure ▁of ▁the ▁majority ▁of ▁the ▁shell s ▁to ▁det on ate ▁may ▁have ▁had ▁various ▁causes . ▁As ▁the ▁sub mar ines ▁fired ▁arm our - p ier cing ▁shell s , ▁intended ▁for ▁use ▁against ▁steel ▁ship ▁h ull s , ▁the ▁relatively ▁so fter ▁brick ▁walls ▁may ▁have ▁failed ▁to ▁trigger ▁the ▁impact ▁f uses . ▁Sea ▁water ▁may ▁have ▁de grad ed ▁the ▁shell s , ▁which ▁the ▁Japanese ▁had ▁stored ▁in ▁deck ▁lock ers ▁for ▁several ▁weeks . ▁The ▁age ▁of ▁the ▁shell s ▁may ▁also ▁have ▁been ▁a ▁factor ; ▁some ▁of ▁the ▁shell s ▁recovered ▁from ▁the ▁New castle ▁bomb ard ment ▁were ▁found ▁to ▁be ▁of ▁English ▁manufact ure : ▁sur plus ▁m un itions ▁from ▁World ▁War ▁I . ▁ ▁In ▁Sydney , ▁fear ▁of ▁an ▁imp ending ▁Japanese ▁invasion ▁caused ▁people ▁to ▁move ▁west ; ▁housing ▁prices ▁in ▁the ▁Eastern ▁Sub ur bs ▁dropped , ▁while ▁those ▁beyond ▁the ▁Blue ▁Mountains ▁rose ▁significantly . ▁The ▁attack ▁also ▁led ▁to ▁a ▁significant ▁increase ▁in ▁the ▁membership ▁of ▁volunte er ▁defence ▁organis ations , ▁and ▁strength ening ▁of ▁def ences ▁in ▁Sydney ▁Har bour ▁and ▁Port ▁New castle .