<P> 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 . </P>
<P> 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 . </P>
when did japan start planning the attack on pearl harbor
when did japan start planning the attack on pearl harbor
early spring 1941
early spring 1941