when did japan start planning the attack on pearl harbor
Attack on Pearl Harbor 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.[38] 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.[39] 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.[40] The planners studied the 1940 British air attack on the Italian fleet at Taranto intensively.[nb 7][nb 8]
Attack on Pearl Harbor The Japanese attack had several major aims. First, it intended to destroy important American fleet units, thereby preventing the Pacific Fleet from interfering with Japanese conquest of the Dutch East Indies and Malaya and to enable Japan to conquer Southeast Asia without interference. Second, it was hoped to buy time for Japan to consolidate its position and increase its naval strength before shipbuilding authorized by the 1940 Vinson-Walsh Act erased any chance of victory.[51][52] Third, to deliver a blow to America's ability to mobilize its forces in the Pacific, battleships were chosen as the main targets, since they were the prestige ships of any navy at the time.[51] Finally, it was hoped that the attack would undermine American morale such that the U.S. government would drop its demands contrary to Japanese interests, and would seek a compromise peace with Japan.[53][54]