sub marine ▁bo om ▁net ▁between ▁George ' s ▁Head ▁on ▁Middle ▁Head ▁and ▁Green ▁Point ▁on ▁Inner ▁South ▁Head . ▁The ▁central ▁section ▁of ▁the ▁net ▁was ▁complete ▁and ▁support ▁p iles ▁were ▁in ▁place ▁to ▁the ▁west , ▁but ▁ ▁wide ▁g aps ▁remained ▁on ▁either ▁side . ▁Material ▁short ages ▁prevent ed ▁the ▁completion ▁of ▁the ▁bo om ▁net ▁prior ▁to ▁the ▁attack . ▁On ▁the ▁day ▁of ▁the ▁attack , ▁the ▁six ▁outer ▁indicator ▁loops ▁were ▁in active ; ▁two ▁were ▁not ▁function ing ▁and ▁there ▁were ▁not ▁enough ▁trained ▁personnel ▁to ▁man ▁both ▁the ▁inner ▁and ▁outer ▁loop ▁monitoring ▁stations . ▁The ▁North ▁Head   – ▁South ▁Head ▁indicator ▁loop ▁had ▁been ▁giving ▁fault y ▁signals ▁since ▁early ▁ 1 9 4 0 , ▁and ▁as ▁civil ian ▁traffic ▁regularly ▁passed ▁over ▁the ▁loop , ▁read ings ▁were ▁often ▁ignored . ▁ ▁Har bour ▁defence ▁craft ▁included ▁the ▁anti - sub marine ▁vessels ▁ ▁and ▁B ing era ; ▁the ▁auxili ary ▁mines we ep ers ▁H MA S ▁Go on am be e ▁and ▁; ▁pleasure ▁launch es ▁converted ▁to ▁channel ▁pat rol ▁boats ▁( and ▁armed ▁with ▁depth ▁charges ), ▁namely ▁, ▁L ol ita , ▁Ste ady ▁H our , ▁, ▁Mar lean , ▁and ▁; ▁and ▁four ▁un ar med ▁auxili ary ▁pat rol ▁boats . ▁ ▁P rel ude ▁ ▁The ▁Japanese ▁Navy ▁used ▁five ▁Ko - hy ote ki - class ▁m idget ▁sub mar ines ▁in ▁an ▁un success ful ▁operation