 <translate> 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. <yor> Apá tó ṣe pàtàkì nínú ìdáhùn sí ìbéèrè yìí ni pé: Ìṣètò ìṣáájú fún ìkọlù Pearl Harbor láti dáàbò bo ìgbésẹ̀ náà sí "Àgbègbè Ìpèsè ti Gúúsù" (ìyẹn ni orúkọ tí àwọn ará Japan ń pe Ìlà Oòrùn Íńdíà ti Netherlands àti Gúúsù Ìlà Oòrùn Éṣíà lápapọ̀) ti bẹ̀rẹ̀ ní ìbẹ̀rẹ̀ ọdún 1941 lábẹ́ ìdarí Admiral Isoroku Yamamoto, tó ń darí Ẹgbẹ́ Òkun Àpapọ̀ ti Japan nígbà yẹn. Ìdáhùn tó gbẹ̀yìn ni pé, ní ìbẹ̀rẹ̀ ọdún 1941. 