 Japanese strategic scouting arrangements prior to the battle were also in disarray . A picket line of Japanese submarines was late getting into position ( partly because of Yamamoto 's haste ) , which let the American carriers reach their assembly point northeast of Midway ( known as " Point Luck " ) without being detected . A second attempt at reconnaissance , using four @-@ engine <unk> " Emily " flying boats to scout Pearl Harbor prior to the battle and detect whether the American carriers were present , part of Operation K , was thwarted when Japanese submarines assigned to refuel the search aircraft discovered that the intended refueling point — a hitherto deserted bay off French Frigate Shoals — was now occupied by American warships , because the Japanese had carried out an identical mission in March . Thus , Japan was deprived of any knowledge concerning the movements of the American carriers immediately before the battle . 
