Prologue Magazine

The Z Plan Story

Japan's 1944 Naval Battle Strategy Drifts into U.S. Hands, Part 2

Fall 2005, Vol. 37, No. 3

By Greg Bradsher

Refer to Caption U.S. Army Lt. Col. James M. Cushing radioed General MacArthur on April 9, 1944, about his worsening situation. (Records of General Headquarters, Southwest Pacific Area and United States Army Forces, Pacific (World War II), RG 496)

About midnight, Cushing informed SWPA that the prisoners were too hot to hold and due to number of civilians being killed he was making terms that civilians were not to be molested in the future in exchange for the prisoners. He noted that his small force of 25 soldiers was unable to stand up against an attacking force of 500, and he pointed out that in southern Cebu some 2,000 Japanese were looking for the prisoners. Again, through delays, this message did not reach Brisbane until April 12, after the prisoners had been returned to the Japanese.

On the morning of April 10, stretcher-borne Fukudome and the nine other prisoners started the trip back to the Japanese lines, about six miles from Cebu City. At noon they were turned over to the Japanese. When their escorts returned to Cushing, they carried two messages. One from Ohnisi offering thanks for treating the prisoners kindly and one from the "general" extending his best regards. Fukudome rested at Cebu City and flew to Manila on April 15. Five days later, he departed for Tokyo. The other survivors flew to Saipan and then to Tokyo to be questioned about the incident. Ohnisi observed a three-day cease fire with the guerrillas, and after the conflict renewed ordered his troops to avoid attacking civilians.

Throughout April 10 Cushing awaited word from SWPA regarding his actions, for which he knew would be criticized. Because of the delay in sending and receiving messages to and from SWPA in Brisbane, Cushing began receiving instructions on April 11 on how to get the prisoners back to Brisbane even after he had released them. Eventually, by April 14, top officials in Brisbane realized that Cushing had been forced to act quickly without waiting for their long-delayed instructions. In Brisbane, the "Koga affair" was closed. It also ended for the Japanese, for on April 17 the acting commander in chief of the Japanese Combined Fleet reported to the Navy General Staff in Tokyo that the search for Koga was ended, and the "Otsu incident" was closed.

But it was not over in the Philippines.

* * *

After Fukudome and the other prisoners were returned to the Japanese, Cushing turned his attention to the recovered documents, including the Z Plan, which had been delivered to him by guerrillas on April 9 or 10. The plan's appearance—the red leather portfolio embossed with an elaborate emblem and documents stamped with seals—led Cushing to believe the documents were very important. He had them rolled tightly and placed inside two empty mortar shells to protect them from the elements. He then sent a message to SWPA on April 13 about these documents and others in his possession.

Cushing reported to Brisbane that he had two relatively recent Japanese operations maps, showing air bases, naval bases, wireless stations, emergency landing fields, triangulation points, heights, and more. These maps covered Palau, the Philippines, most of French Indo-China, Hainan Island, and South China. He would send the maps, along with papers and field orders taken from prisoners, to his superior, Lt. Col. Edwin D. Andrews on southern Negros, and they would arrive there in approximately two weeks.

When SWPA received Cushing's message on April 14, Whitney wrote to Brig. Gen. Charles A. Willoughby, MacArthur's chief of intelligence (G-2), that the documents would be available for dispatch on a supply trip by the submarine Narwhal about the end of May unless Willoughby wanted them earlier. Willoughby responded that the documents sounded as if they might be extremely valuable and suggested they be brought to Brisbane at the earliest opportunity. On April 18 SWPA instructed Cushing to take every possible precaution to ensure the documents' safe arrival at southern Negros for dispatch to SWPA and asked him to advise when delivery was completed.

After sending his April 13 message, Cushing gave the mortar shells with the documents inside to two former American prisoners of war, Russ Snell and Jimmy Dyer, and told them to take them to Andrews's headquarters. There, he believed, the two men, along with the documents, would be shipped back to Australia by a submarine regularly making runs to Negros. On April 15 the two, along with a bodyguard of soldiers, set out. They crossed Cebu and then the Tanon Strait, and arrived on April 28 at Andrews's headquarters in the hills behind the coastal village of Culipapa. They turned over to Andrews the mortar shells containing the documents.

On April 27 Cushing sent another message to SWPA informing it that through the help of fishermen they had recovered more documents from the crashed seaplane and that he was sending them to Andrews's headquarters.

Meanwhile, the Japanese, having given up their search for Koga, were still concerned about the missing documents they believed were on Cebu. They even offered a reward of 50,000 pesos (about $25,000).

When Whitney, Willoughby, and SWPA Chief of Staff Lt. Gen. Richard Sutherland heard about the reward and the additional documents, they concluded the documents might be quite valuable. Whitney immediately sent a message to Andrews telling him that the documents "may be of considerable value" and asked about the advisability of sending them via regular or special pickup.

Cushing on May 1 sent a message to SWPA that he was sending more documents to Col. Wendell Fertig's headquarters. Fertig commanded all guerrillas on Mindanao. From there, apparently, Cushing believed they could be forwarded to Negros. "We are," Cushing added to his message, "attempting interception to meet your carriage."

The next day, Cushing notified SWPA that the most important documents had made it to Andrews and that more documents were on their way. This message was received at SWPA on May 4. Immediately Whitney notified Sutherland about the message and indicated they would not be able to pick them up on a regular supply mission until about the middle of the next month due to unexpected delay in Narwhal refitting. He asked Sutherland if he should endeavor to arrange an earlier special pickup, and the next day Willoughby recommended to Whitney that the documents be picked up at the earliest opportunity. But the following day, in a message to Sutherland, Willoughby cautioned that while a special pickup may be warranted, they should "avoid blowing up their importance any more than is absolutely necessary to assure security, to minimize the danger of the enemy acquiring knowledge that we have actually recovered them. The value of the documents may well largely depend upon our ability to keep such information from the enemy."

On May 5, the Japanese publicly announced Koga's death and the appointment of Soemu Toyoda as Combined Fleet commander. The announcement indicated that Koga had been killed in action in March while directing naval operations from a plane.

Whitney began connecting the dots between the public announcement of Koga's loss, Cushing's past messages, and the intercepts regarding the "Otsu incident," the documents, and the high reward for the documents. He immediately wrote to Sutherland, urging that the documents with Andrews may be of such great importance that there should be a special pickup. Sutherland agreed, and the Navy informed SWPA that the USS Crevalle, patrolling off the coast of northern Borneo, was the nearest submarine. At 11:30 p.m. on May 7, it received top-secret orders to proceed north to the eastern part of Sulu Sea and to be prepared for a special mission on May 11.

Someone, perhaps Whitney, suggested using the evacuation of American refugees as a cover for the submarine's real mission. Late on the afternoon of May 8, instructions were radioed to the Crevalle to proceed to a position just north of Basay, Negros, and at sunset on May 11, after observing security signals, surface and receive from native sailboats about 25 passengers and important documents. The day before, Whitney sent a message to Salvador Abcede, commander of the Seventh Military District on Negros, that SWPA desired the documents as soon as possible and asked what site would be used for the pickup of the documents and refugees on May 11. Abcede was told to exercise great caution in executing the mission and to "preserve utmost secrecy concerning documents." SWPA followed up with precise instructions on how the transfer of the documents and the refugees was to take place.

About 4:30 p.m. on May 11, the Crevalle was in position for the pickup. Through its periscope, the captain, Lt. Comdr. Francis David Walker, Jr., saw boats and people on the beach, and at 5 p.m. he saw two large boats and some small outriggers heading to the pickup point. When Abcede came aboard at 5:57 p.m., he told Walker that there were 41 people, all American citizens (including 21 children and 8 women) to pick up, not 25, and asked if Walker could take that many. Walker, answering affirmatively, suggested they be hurried aboard. At 5:59 p.m., 40 evacuees (a minister decided to stay behind), including Snell and Dyer, began boarding the submarine. Abcede gave Walker a small wooden box and told him that it contained extremely important documents captured from the Japanese on Cebu and that MacArthur was most anxious to see them. At 6:37 p.m. the submarine got under way.

During the trip to Australia, Walker kept the submarine on the surface as much as he could for greater speed. Several times it had to submerge as it was sighted and attacked by Japanese aircraft and ships, twice surviving severe depth chargings.

Refer to CaptionThe USS Crevalle.(80-G-447516)

While the Crevalle was making its way to Australia, Cushing on May 14 sent a message to SWPA reporting that the second batch of documents from the crash of the Japanese plane had arrived too late to be included with the first batch of documents already on their way to Brisbane. He indicated that the second batch had been sent to Mindanao. Whitney on May 17 informed Sutherland that the first batch of documents should arrive in two days and from them Willoughby should be able to determine the desirability of arranging a second special pickup or leaving it to a regular supply run.

Early on May 19, the Crevalle neared the Australian coast, and two small Australian navy boats headed toward it. The Crevalle stopped, and Comdr. X. M. Smith, who headed the American base at Darwin, came aboard and informed Walker that he was there to pick up the "mail" brought from Negros. Smith took the wooden box, signed a receipt, and his boat immediately headed to Darwin. Smith gave the box to a courier, who rushed it to the nearby airport, and some six hours and 1,800 miles later, the plane landed at Brisbane. By midday the box of Japanese secrets was in Whitney's hands.

* * *

When the box was opened and the documents laid out, the American intelligence personnel were pleased to see they were in plain language, not code. Very quickly, it was apparent that its contents were extremely sensitive. The portfolio and the red covers on some of the documents were sure signs of highly classified material.

On May 21, Whitney sent the documents to Willoughby, who forwarded them to Col. Sidney F. Mashbir, the head of the Allied Translation and Interpreter Section (ATIS), for the highest priority translation and interpretation.

That morning, at ATIS headquarters at Indooroopilly, a Brisbane suburb, photostatic copies of the documents were made and given to Mashbir's top five translators. They quickly identified one document as copy six of 550 copies of "Secret Combined Fleet Order No. 73." It had been issued on March 8, 1944, from the flagship Musashi at Palau and was signed by Koga, the commander in chief of the Japanese Combined Fleet. The preamble greatly excited them, as it stated:

  • The Combined Fleet is for the time being directing its main operations to the Pacific Area where, in the event of an attack by an enemy Fleet Occupation Force, it will bring to bear the combined maximum strength of all our forces to meet and destroy the enemy, and to maintain our hold on vital areas.
  • These operations will be called "Z Operations."

They labored over the rest of the document, for not only did it contain Japanese place names for islands (e.g., Wake was Otori), but it contained many naval terms whose meaning was not always clear to Army men. All day and night on May 21 and the next day the translators worked.

While the translation was under way, Cushing on May 22 radioed SWPA to report that the Japanese knew his men had found more documents. Takeshi Watanabe, the Japanese naval commander in Cebu, had an airplane drop leaflets, dated May 17 and addressed specifically to Cushing, across the island instructing that all documents, bags, and clothing either picked up from the airplane that had made a forced landing off San Fernando, Cebu, on April 1 or robbed of the passengers and the crew be returned unconditionally by noon on May 30 to the mayor of San Fernando for safekeeping. If Cushing did not comply, the Japanese navy would resort to "drastically severe" methods against them.

Whitney sent a copy of Cushing's message to Sutherland on May 23, adding that it showed the value of the documents in Japanese eyes. He informed Sutherland that ATIS was translating the documents and that they appeared to contain a file of Japanese Combined Fleet operational orders and a file of naval dispatches. He added that other documents from the same recovery arrived too late for the May 11 pickup and that the Navy was arranging a special pickup for them.

When Willoughby saw the translation on May 22, he was excited at having the Japanese navy plans in his hands. Either that night or the next morning, Mashbir operated a hand-cranked mimeograph machine to run off 20 copies of the 22-page translation, and on May 23 ATIS issued Limited Distribution Translation No. 4 "Z Operation Orders." The first copy went by officer courier to Gen. George C. Marshall, chief of staff of the U.S. Army. The second copy went to MacArthur.

Refer to Caption Limited Distribution Translation No. 4 gave American commanders their first look at Japan s Z Plan. (Records of General Headquarters, Far East Command, Supreme Commander Allied Powers, and United Nations Command, RG 554)

Once the Z Plan document was translated and published, the ATIS translating team tackled the packet of documents containing "A Study of the Main Features of Decisive Air Operations in the Central Pacific." On May 25 the ATIS team sent Mashbir its 29-page translation of this document as well as collateral notes and other documents from the packet. These documents were published on May 28 as ATIS Limited Distribution Translation No. 5.

After reading the two publications, Willoughby, Sutherland, and MacArthur were impressed with the high-level strategy put forth in the documents but were not completely sure what it all meant. Capt. Arthur McCollum, the Seventh Fleet's director of intelligence and Navy liaison with Whitney's Philippine Regional Section, however, did. He immediately saw the importance of the translations and realized that Adm. Chester Nimitz, commander in chief of the Pacific Fleet, needed to see them as soon as possible. He asked SWPA to send copies to the Joint Intelligence Center Pacific Ocean Area (JICPOA) at Pearl Harbor. Sutherland agreed and arranged for copies of the published translations to be sent to JICPOA. An Army bomber flew nearly 5,000 miles in 48 hours, stopping at various islands to refuel, to deliver the copies to Pearl Harbor.

At Pearl Harbor, the translations were delivered to Capt. Edwin T. Layton, Nimitz's Fleet intelligence officer. Layton saw the bold stamp on the translations: "Top Secret. Not to be copied or reproduced without permission of General MacArthur." Immediately, under Nimitz's signature, Layton sent a message to SWPA asking MacArthur's approval to distribute the translations. Although he recognized that the translations had been made by someone unfamiliar with Japanese naval terminology, it was evident that the captured documents were the Japanese Combined Fleet's operational plans for concentrating its total sea and air strength against next American advance into the Japanese island defense system.

As the Fifth Fleet and the Marianas invasion forces were already assembling at Eniwetok, Layton believed quick action was needed and that a retranslation had to be as correct as possible before it was distributed. He radioed Mashbir and asked for photostats of the original Japanese documents. Two days later, with the photostats in hand, Layton and a small group of JICPOA translators retranslated the entire Z Plan. When finished, Layton believed that ATIS had gotten it mostly right.

It was plain to Layton that the Japanese planned to hurl everything they had against the American fleet. Layton immediately presented his findings and the documents to Nimitz. He had copies mimeographed and sent at once, with a cover letter, to every flag officer associated with the planned Marianas invasion. A flying boat rushed copies of Layton's translation with Nimitz's final instructions out to the task force at Eniwetok. It arrived on June 8 and delivered to Adm. Raymond A. Spruance, commander of the Fifth Fleet, aboard his flagship the Indianapolis. The translations arrived too late to reach Task Force 58, under Vice Adm. Marc A. Mitscher, before it departed Majuro in the Marshall Islands, but copies were air-dropped to his flagship Lexington on the high seas. Spruance and Mitscher were therefore well aware of the enemy strategy when they set course north across the Philippine Sea for the Marianas.

Admiral Koga's plan was inherited by Adm. Soemu Toyoda, who had been appointed on May 1 as the new commander in chief of the Combined Fleet. Within a week after he took command, he modified the old Z Plan slightly to provide for a battle area in the western Carolines or Marianas, renaming it the A Operation (or A-Go). His plan provided for concentrating Japanese shore-based air forces and to operate his carrier planes from shore bases when the Americans attacked the Philippines, Palau, or the Marianas. He also planned to use his empty carrier forces as a diversionary attack force to draw off American carrier forces while the Japanese surface fleet fell upon and destroyed the Americans.

The Japanese could not help but know about the American forces steaming their way toward the Marianas. The American force consisted of 535 ships (including 15 carriers with 900 planes) and 127,571 troops, making Operation Forager the largest amphibious assault yet mounted in the Pacific. It began with an air strike on Saipan on June 15. To meet the American threat, Toyoda, who had six carriers and some 450 airplanes, intended to use airfields on Tinian and Guam while he rushed in his reserve of land-based planes from Japan, using the Bonin Islands as way stations.

An elaborate decoy operation was supposed to lure U.S. forces westward, but Spruance did not take the bait. His primary task was to protect the Saipan beachhead. He knew from the captured documents that if he went full tilt after the Japanese fleet some 600 miles west of Guam, the enemy carrier planes would be able to multiply their effectiveness by using the other airfields in the Marianas for shuttle-bombing runs. It would also expose him to attack from land-based planes flying south from Japan. Instead he waited for the Japanese to come for him, and they did. The major battle, the greatest carrier battle of the war, took place on June 19–20 in the Philippine Sea, west of the Marianas. The American fleet dealt a major defeat to the A-Go operation during the so-called "Marianas Turkey Shoot," shooting down some 476 Japanese planes and forcing the Japanese fleet to flee westward.

* * *

Back at SWPA, Whitney wrote Sutherland on May 25 that the last increment of documents had left Cushing and were then en route to southern Negros, where they would be picked up by an operational submarine. Four days later, Abcede radioed that some documents had arrived and that Cushing indicated that his couriers were coming with more documents.

The Japanese continued to look for the documents on Cebu. Near the end of May, even before the May 30 ultimatum expired, the Japanese stepped up their bombing and strafing. On May 30 the Japanese dropped leaflets on the guerrillas, indicating they had "decided to resort to the firm and drastic measures against you. Our offensive, from now on, will increase extremely in its vigor and fierceness." On June 3 Cushing radioed SWPA that the Japanese had taken his headquarters by surprise on May 30 and that his forces had sustained several casualties in their escape. He also noted that the Japanese were burning many homes on Cebu. Later that day, Cushing radioed SWPA that all additional documents were then at Andrews's headquarters and that the Japanese were using nine planes in the current drive against his forces. He noted that he might be forced off the air as the Japanese were then 13 hours away from him.

On June 4 Whitney informed Sutherland that all of the remaining documents had been delivered to southern Negros, and plans called for the pickup of the documents in about 10 days.

While the submarine pickup plans were being developed, Cushing's forces were continually under Japanese fire. On June 16, Cushing informed SWPA that the bombing and strafing continued until June 12, and since then there was day and night plane activity over Cebu. Apparently the Japanese had not given up on finding any captured documents the guerrillas had recovered.

Eventually the second batch of documents were picked up and delivered to MacArthur's headquarters in Australia. The documents consisted of two volumes of typewritten and penciled radio messages that had been received and decoded. The messages were between various naval units from the end of 1943 to March 29, 1944, with code symbols on the messages. The messages were primarily about the change of codes of Japanese fleet units and radio broadcasts and appeared to be of primary value to the Central Bureau, the Allies' code-breaking unit in SWPA.

* * *

After resting for a month after returning to Japan, Fukudome was appointed in June 1944 as the commander in chief of the Second Air Fleet and served in that capacity until January 1945, at which time he became commander in chief of the Tenth Area Fleet. He survived the war. Cushing, leading his Cebu guerrillas, also survived the war.

On February 1, 1945, ATIS informed Willoughby that the Z Plan story had been released to the press and that the plan was "probably one of the most important documents captured in SWPA to date."

How important knowledge of the Japanese strategy was to the American victory at the Battle of the Philippine Sea is impossible to answer. However, historians acknowledge that the exploitation of the Z Plan was one of the greatest single intelligence feats of the war in the Southwest Pacific Area.

The "Z Plan" Story, Part 1

Greg Bradsher, an archivist at the National Archives and Records Administration, specializes in World War II intelligence, looted assets, and war crimes. Dr. Bradsher's previous contributions to Prologue have been "Taking America's Heritage to the People: The Freedom Train Story" (Winter 1985); "Nazi Gold: The Merkers Mine Treasure" (Spring 1999); and "A Time to Act: The Beginning of the Fritz Kolbe Story, 1900–1943" (Spring 2002).

Note on Sources

Steven Trent Smith's The Rescue: A True Story of Courage and Survival in World War II (Hoboken, NJ: John Wiley & Sons, 2001) provides a very detailed account of the Z Plan story, focusing on the individuals rescued by the Crevalle. The activities of the Crevalle are documented in the Report of Special Mission, May 9–12, 1944, USS Crevalle (SS291), Records of the Office of the Chief of Naval Operations (Record Group 38).

A postwar interrogation of Fukudome is contained in the Records of the U.S. Strategic Bombing Survey (Record Group 43). Messages to and from Cushing and related memorandums are contained in GHQ Messages in the Guerrilla Resistance Movement in the Philippines, Cushing to MacArthur and GHQ Messages in the Guerrilla Resistance Movement in the Philippines, MacArthur to Cushing, Records of General Headquarters, Southwest Pacific Area and United States Army Forces, Pacific (Record Group 496). Other related correspondence can be found in the Records of the Assistant Chief of Staff, G-2, Military Intelligence Section and the records of G-2, Philippine Section, both in Record Group 496.

Articles published in Prologue do not necessarily represent the views of NARA or of any other agency of the United States Government.

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