Z Plan ( Japan ) The Z Plan ( ) was the Japanese plan of attack in the case of an American invasion into the central Pacific ocean . The plan was the final attempt by the Japanese to bring about the Kantai Kessen , the decisive battle that would be the avenue of victory for Japan . The capture of these plans were an important military intelligence achievement in the Pacific War . The Z Plan was developed under the leadership of Admiral Mineichi Koga , commander in chief of the Japanese Combined Fleet , and was approved by the Imperial Japanese Navy General Staff . The plan was formally titled : Combined Fleet Secret Operations Order No . 73 , with the final version issued on March 8 , 1944 . On April 1 , en route to Davao , Admiral Koga ' s plane crashed into the ocean during a bad storm , killing Koga and everyone else aboard . Admiral Koga ' s chief of staff , Rear Adm . Shigeru Fukudome , carrying a copy of the Z Plan , was traveling the same itinerary in a separate plane . This second plane crashed near Cebu Island after attempting to avoid the same storm . Fukudome and nine others eventually made it to shore , where they were captured by local Filipino guerrilla s who were supportive of the U . S . forces . Because of the loss of the two planes , with their high - level occupants and important documents ( Japanese ocean - current experts believed documents would eventually wash - up on shore ) , the Japanese applied intensive pressure on the local population . Partially as a result of this pressure , Fukudome and the others were eventually released . On April 3 , a wooden box from Fukudome ' s plane washed up near shore , and was secretly recovered by two villagers . The box contained the Z plan , a bound document in a red leather portfolio , with a Z on the cover . The documents eventually made it into the hands of the local guerrilla organization , the Cebu Area Command , under Lt . Col . James M . Cushing . The ornate nature of the documents led the CAC and their American handlers to suspect the documents were very important , a suspicion that was later reinforced by Japan ' s offer of a large reward for the return of any documents . A clandestine high - priority submarine pickup was arranged , with a cover story of evacuating American refugees . The submarine picked up the documents , along with 40 American men , women and children . Traveling mostly on the surface for speed , and diving only when needed , the submarine survived depth charging twice , arriving near the American naval base in Darwin , Australia on May 19 . From there the documents were flown to Brisbane . The Z Plan documents were in plain text , rather than code , and were translated on an urgent basis by the top five translators at the Military Intelligence Service attached to the Allied Translator and Interpreter Section , it was first translated by Yoshikazu Yamada and George " Sankey " Yamashiro , two nisei translators . Copies of the translation were rushed to General Douglas MacArthur , who quickly forwarded them to Admiral Chester Nimitz , commander in chief of the Pacific Fleet ( and Admiral Kogo ' s counterpart ) . Among other things , planned Japanese diversionary tactics were now anticipated by the Americans , leading to the lopsided American victory in the Battle of the Philippine Sea , the largest aircraft carrier battle in history , and one of the decisive battles of the Pacific war .