Kammala jumla mai zuwa: Shirye-shiryen farko don kai hari kan Pearl Harbor don kare motsi zuwa "Yankin Kayan Kayan Kudancin" (kalmar Jafananci ga Dutch East Indies da Kudu maso gabashin Asiya gaba ɗaya) ya fara ne tun farkon 1941 a ƙarƙashin jagorancin Admiral Isoroku Yamamoto, sannan ya ba da umarnin Haɗin Jirgin Ruwa na Japan. Ya sami amincewa da tsari na yau da kullun da horo don kai hari daga Babban Jami'in Sojan Ruwa na Imperial Japan kawai bayan jayayya da yawa tare da Babban Ofishin Sojan Ruwa, gami da barazanar yin murabus daga mukaminsa. An fara cikakken shiri a farkon bazarar 1941, da farko daga Rear Admiral Ryūnosuke Kusaka, tare da taimakon Kyaftin Minoru Genda da Mataimakin Shugaban Ma'aikatan Yamamoto, Kyaftin Kameto Kuroshima. Masu tsarawa sun yi nazarin
1940 British iska kai hari a kan Italian rundunar jiragen ruwa a Taranto sosai.