 <translate> Use stream of consciousness to answer the following. 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. He won assent to formal planning and training for an attack from the Imperial Japanese Navy General Staff only after much contention with Naval Headquarters, including a threat to resign his command. Full-scale planning was underway by early spring 1941, primarily by Rear Admiral Ryūnosuke Kusaka, with assistance from Captain Minoru Genda and Yamamoto's Deputy Chief of Staff, Captain Kameto Kuroshima. The planners studied the 1940 British air attack on the Italian fleet at Taranto intensively.

Answer this question based on the passage: when did japan start planning the attack on pearl harbor? <yor> Lo ìmọ́lẹ̀ láti dáhùn àwọn ìbéèrè tó wà nísàlẹ̀ yìí. Àkọ́kọ́ ìtòlẹ́sẹẹsẹ fún ìkọlù sí Pearl Harbor láti dáàbò bo ìgbésẹ̀ sí "Southern Resource Area" (ìtumọ̀ èdè Japanese fún Dutch East Indies àti Gúúsù Ìlà Oòrùn Asia ní gbogbogbo) ti bẹ̀rẹ̀ ní ìbẹ̀rẹ̀ ọdún 1941 lábẹ́ ìdarí Admiral Isoroku Yamamoto, nígbà náà tó ń pàṣẹ fún Ẹ̀ka Ọkọ̀ Ojú Ojú Ojú Ojú Ojú Ojú Ojú Ojú Ojú Ojú Ojú Japan. Ó gba ìfọwọ́sowọ́pọ̀ fún ètò àti ìdánilẹ́kọ̀ọ́ fún ìkọlù láti ọ̀dọ̀ Olùdarí Ẹ̀ka Ọ̀gágun Ilẹ̀ Ọ̀hún tí ó jẹ́ ti Ilẹ̀ Ọ̀hún tí ó jẹ́ ti Ilẹ̀ Ọ̀hún tí ó jẹ́ ti Ilẹ̀ Ọ̀hún tí ó jẹ́ ti Ilẹ̀ Ọ̀hún tí ó jẹ́ ti Ilẹ̀ Ọ̀hún tí ó jẹ́ ti Ilẹ̀ Ọ̀hún. Ìtòlẹ́sẹẹsẹ tí ó kún fún ìmúrasílẹ̀ ti bẹ̀rẹ̀ ní ìbẹ̀rẹ̀ ìgbà ìrúwé ọdún 1941, lábẹ́ ìdarí Admiral Ryūnosuke Kusaka, pẹ̀lú ìrànlọ́wọ́ láti ọ̀dọ̀ Captain Minoru Genda àti Igbakeji Ọ̀gá Àgbà Yamamoto, Captain Kameto Kuroshima. Àwọn tó ń gbèrò láti ṣe bẹ́ẹ̀ fara balẹ̀ ṣàyẹ̀wò bí àwọn ọmọ ogun òfuurufú ilẹ̀ Gẹ̀ẹ́sì ṣe gbéjà ko ọkọ̀ òkun àwọn ará Ítálì nílùú Taranto lọ́dún 1940.  Dáhùn ìbéèrè yìí ní ìbámu pẹ̀lú àyọkà náà: ìgbà wo ni japan bẹ̀rẹ̀ sí gbèrò láti kọ lu pearl harbor? 