 
<translate> Muhimmin bangare don amsa wannan tambayar shine: Shirye-shiryen farko don kai hari kan Pearl Harbor don kare motsi zuwa "Yankin Kayan Kayan Kudancin" (kalmar Jafananci don 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. Amsar ita ce: A farkon shekara ta 1941. <eng> The important part for answering this question is: Preliminary planning for an attack on Pearl Harbor to protect the move into the "Southern Resource Area" (the Japanese term for the Dutch East Indies and Southeast Asia generally) had begun very early in 1941 under the auspices of Admiral Isoroku Yamamoto, then commanding Japan's Combined Fleet. Final answer: very early in 1941. 