The Japanese code names followed a pattern—Rabaul was “RR,” and the code names for the islands around Rabaul started with R; Palau was “PP”, and its associated islands began with P. Rochefort guessed that the Japanese were assembling an invasion fleet to take Port Moresby—MO—on Papua New Guinea and perhaps establishing new bases farther into the Pacific in order to cut off and invade Australia. Thus advised, Admiral Nimitz and Layton realized that if they were able to get a task force down to thwart the invasion of Port Moresby, not only would they save Australia from the encroaching Japanese stranglehold, but they might be able to isolate part of the Kido Butai’s carrier force and defeat it in detail.
For their part, the Japanese offensive plan for the war had gone off so successfully and with so few losses that they were scrambling to determine what to do next. Although they knew there would be much fighting ahead, with their initial missions accomplished, a triumphal mentality set in that would become known as “shōribyō,” or victory disease. The Naval General Staff in Tokyo made plans to invade Australia, but dropped the idea when it became clear that the Japanese army wouldn’t spring ten divisions from the occupation of Manchuria. So they developed more modest plans to invade New Guinea, Fiji, New Caledonia, and the Solomons, starting with Port Moresby, where they could set up bases to raid convoys supplying Australia and stage long-range bombing patrols on enemy warships and the Australian mainland.
In contrast, the Combined Fleet officers’ priority was to create a ring of mutually supporting defensive positions out of the various island chains—unsinkable aircraft carriers—spread throughout the vast ocean. Their argument was that concentrating naval power in the south would leave the Japanese mainland open to carrier raids from the central and barren North Pacific—just as they had attacked Pearl Harbor. But if the Japanese were able to make a base in the Aleutians and take Midway Island, then Oahu, they would rule the Pacific. Since the Combined Fleet’s planners had gained almost insurmountable credibility with the raid on Pearl Harbor, the Naval General Staff acceded to their demands. The seeming necessity for taking Midway was punctuated with new urgency when Captain Jimmy Doolittle led his famous bomber raid on Tokyo and other parts of the Japanese mainland on April 18, 1942. When FDR was asked whether the bombers came from an island in the Pacific or from mainland China, he merely answered “Shangri-La.” But Doolittle’s ordinarily land-based B-25 bombers had taken off from the aircraft carrier Hornet in a task force led by Admiral William “Bull” Halsey hundreds of miles from the Japanese coastline.
The Japanese public was shocked that American bombers could somehow reach across thousands of miles, and that the Americans would have the audacity to make war on their sacred homeland. Even though the raid destroyed little of Japan’s war-making infrastructure, the effects loomed far out of proportion. The supremely confident militarists had egg on their face, and took steps to recall pilots and their airplanes back to the homeland. All available Japanese navy ships went on a wild-goose chase for the carriers, burning precious fuel and wasting valuable time. The raid also had the effect of making the high command shift resources away from where they would be most valuable, and delayed their other offensive operations, which gave the Americans invaluable breathing space. During this time, the Kido Butai was occupied with British targets in the Indian Ocean, and Nimitz’s carriers Enterprise and Lexington were able to stage hit-and-run raids against the Marshall Islands with relative impunity. This caused much consternation among the upper echelons of the Japanese navy, upsetting their offensive plans even further.
Rochefort now told Layton that after the Kido Butai’s successful Indian Ocean campaign, the aircraft carriers Shokaku and Zuikaku would be going to Truk instead of Japan. This suggested that after becoming aware of the presence of Enterprise and Lexington in the Marshalls, the Japanese might reinforce the MO invasion force and its escort carrier “Ryukaku” with the Shokaku and Zuikaku. The odds then would be against the Americans three to two. For a force with a total of four aircraft carriers in the Pacific* versus an estimated eight for the Japanese, the loss of even one aircraft carrier would be a serious blow. But the Allies couldn’t afford to lose Port Moresby or let the Japanese control shipping to Australia, and so the stage was set for the historic Battle of the Coral Sea. The tidings for the Americans were not good the night before battle as they received a radio transmission from the U.S. Navy radiomen in Corregidor:
ONE HUNDRED AND SEVENTY-THREE OFFICERS AND TWENTY-THREE HUNDRED AND SEVENTEEN MEN OF THE NAVY REAFFIRM THEIR LOYALTY AND DEVOTION TO COUNTRY, FAMILIES, AND FRIENDS.
It was Corregidor’s final transmission before the Philippines finally capitulated to the Japanese.
If the stakes hadn’t been so high, the Battle of the Coral Sea would have been characterized as a comedy of errors. The U.S. task force commander Vice Admiral Frank Jack Fletcher chased false leads, split up his forces, and repeatedly ignored the radio intelligence officer on board his own ship. When a reconnaissance plane gave a contact report with a faulty code, Fletcher prematurely launched all the aircraft from his two carriers, Yorktown and Lexington. If Japanese land- or carrier-based planes found them, they would have no defense. When Fletcher discov-ered the error, he flew into a rage. Luckily, MacArthur’s bombers reported a carrier sighting not far off from the original contact report, and Fletcher broke radio silence to redirect them to the new coordinates. They found and sank the “Ryukaku”—in actuality, the smaller escort carrier Shoho—and triumphantly radioed, “Scratch one flattop!” For their part, the Japanese had no radio intelligence to speak of, and although they were nearly within striking distance of the American carriers, their reconnaissance flights were hampered by a fortuitous rainsquall that appeared between the forces. Fletcher’s radio intelligence officer told him exactly where he’d find the Shokaku and Zuikaku, but Fletcher refused to believe him until Japanese planes bombed into oblivion an oiler and destroyer that Fletcher had left behind. Rear Admiral Chuichi Hara, the Japanese commander of Carrier Division Five, discovered Fletcher’s location from the destruction of the Shoho and later by a floatplane report. After expending all their bombs on the hapless American oiler and destroyer, Hara’s planes harmlessly circled the Yorktown and Lexington for a friendly visit. After returning from the attack on the Shoho, the planes of the Yorktown and Lexington refueled and rearmed. Inexplicably, despite the fact that both Fletcher and Hara had a very good idea of where the other was, neither launched an attack until the next morning.
Hara’s planes made an attack on both the Lexington and the Yorktown. The “Lady Lex” was older, larger, and less maneuverable, and the Japanese bombers found their mark as the Lexington slowly turned to evade the bombs. The Yorktown was also heavily damaged, but the Lexington had so many fires that sections of its inch-thick plating actually glowed cherry red in the noonday sun. To keep her from the Japanese, Fletcher sank the ship with torpedoes launched by a destroyer. The Japanese were luckier, but not by much. Although the Shokaku and Zuikaku survived the battle, they were both so damaged that they would need extensive repairs, keeping them out of action for months.
At the outset, it looked as though the Japanese had won yet again, but this time the margins were closer. They had exchanged the smaller escort carrier Shoho for the heavy carrier Lexington. For a navy with an estimated carrier superiority of ten to four, the results favored the Japanese.
There were other, more important developments that threatened the United States fleet, however. The Australian prime minister received Hypo’s weekly intelligence summaries through the Australian navy’s coordination with the Americans. In an effort to quell the fear of a Japanese invasion, he prematurely announced that the invasion of Port Moresby had been called off, and that Australia would have plenty of warning if the Japanese attempted another invasion. How he could have known this so soon after the battle came perilously close to leaking Hypo’s secrets. With an inferior naval force, Nimitz and the Allies had only their superior intellige
nce to avoid catastrophic ambushes and forewarning of invasions, and if the ill-timed words aroused any suspicion that the Japanese code was compromised, now or in the future, it would likely have changed the outcome of the war.
Although the Battle of the Coral Sea didn’t seem like a victory at the time, the results turned out to be advantageous for the Americans. The Shokaku was so damaged as to be put out of action for several months—long enough for the Americans to get some breathing space after so many defeats. In addition, a large number of the Zuikaku’s highly trained and battle-hardened pilots, as well as their planes, were now lost forever, making that ship ineffective until it could get replacements. Another benefit of the Coral Sea engagement was that the Japanese flooded the airwaves with messages encoded in JN-25, which gave Hypo, the Cast team relocated to Melbourne, and Negat in Washington, more examples of the code than they could reasonably handle. More important, it gave Nimitz the confidence he needed to trust the radio intelligence he was getting from Layton, and by extension Joe Rochefort. This confidence would be crucial in the month to come, when on May 11, Rochefort discovered that the Japanese were assembling a massive armada in Saipan. The message specified particular anchorages for the Japanese Second Fleet. Two days later, the term “MI” was associated with an invasion force. The day after that, logistical details turned up when the Japanese navy authorized maps of the Hawaiian Islands chain to be sent to Saipan, as well as another message describing a Koryaku Butai—invasion force—participating in a forthcoming “AF” campaign. From what they could gather, AF served as a submarine base that sent out long-range reconnaissance patrols. This suggested Pearl; Midway, west of Pearl; or Johnston Island, southwest of Pearl. Rochefort also noted messages about the Aleutian Islands chain off Alaska, specifically Attu, Kiska, and Dutch Harbor. Rochefort was convinced that Yamamoto was building up a fantastically elaborate operation, and that the main target was Midway Island.
Back in Washington, Navy Department head Admiral Ernest King expressed doubts, and wanted Nimitz to have Halsey cover the southwest Pacific area in the event that the Japanese continued with their intentions to threaten Australia by taking Fiji, Samoa, and New Caledonia. King was being advised by the ambitious Redman brothers, Joseph and John, who had restructured OP-20-G, the department overseeing the code breakers at Negat, Hypo, and Cast.* As Hypo was part of their fiefdom, they wanted Rochefort to conform to nice organizational charts and do as he was instructed, regardless of whether that marshaled his—or Hypo’s—considerable talents in the most productive way. Their bureaucratic reorganization scheme had its merits in that it geared up OP-20-G to produce intelligence on a massive wartime scale, but it shunted aside Laurance Safford, one of the Navy’s most gifted cryptographers. It also severed several informal personal connections between Negat and Hypo, causing friction and morale problems. The most serious problem was that without Safford, Negat started to misinterpret the radio intelligence about whether AF was Midway.
One of Negat’s objections was that it was entirely too coincidental that the Japanese code for Midway—AF—was suspiciously similar to the Americans’. When they read a Rochefort report that a Japanese unit had requested that their mail be forwarded to their new address at Midway, Negat suggested that Rochefort was falling for Japanese deception and misinformation. They claimed that the A in AF stood for the Aleutians. Then they said it might be Australia. To cover all their bases, they started warning that the West Coast might be the target. With recriminations about the Pearl Harbor disaster running rampant, Admiral King had a knee-jerk reaction to every possible threat, no matter how negligible, and sent Nimitz scrambling with several attack warnings. In addition to the backbreaking work of trying to crack enough of JN-25 to confirm that AF was Midway, determine the Japanese order of battle, and discover when and where they would attack, Rochefort had to do the painstaking task of going over Negat’s many mistakes and misinterpretations to determine where their solutions had gone wrong. The disagreements ignited in what could be called a 1940s flame war until someone pointed out the errors to Admiral King and he finally conceded that AF was Midway. The younger Redman was doubtless humiliated to have his competence called into question. Undaunted, Negat and the Redmans then insisted that the Midway invasion was most likely scheduled for mid-June, and proceeded to fight tooth and nail over that interpretation.
But it was Nimitz’s call, and according to Layton, he was convinced that Rochefort was right from May 14 onward. The problem was that if Rochefort were right, then Negat—and Nimitz’s superior, King—were wrong. Nimitz had to find a way to get Halsey’s task force back to Hawaii for the Midway battle, which was coming soon. Nimitz relied on sleight-of-hand, and sent an “eyes only” message to Halsey hinting that he should somehow get sighted on a course toward Ocean and Noumea islands, where the Japanese were planning an invasion. A seaplane spotted the task force, Halsey got clean away, and once more the Japanese got the jitters about their invasion plans for Ocean and Noumea in New Caledonia, off the Coral Sea.
Rochefort was able to confirm all of this by radio interception and decryption.
Since the invasion plans for Ocean and Noumea were now off, and King was finally convinced that Midway was the new target—albeit at a much later time—Nimitz was able to convince King to bring Halsey’s carriers back to Pearl in time for the Midway invasion. Incredibly, Negat backtracked and started making more ominous warnings that AF may yet be a target in Alaska. Rochefort knew that the Aleutians were also a target, and that to head off any more interference from Washington he needed to prove beyond doubt that AF was Midway. A massive Japanese task force was heading to one of America’s last Pacific outposts while bureaucrats in Washington dithered with inconsequential, vague, and contradictory intelligence assessments.
At this time, Rochefort, Holmes, Finnegan, and Dyer were discussing the Midway problem around one of the Hypo desks when Holmes offhandedly remarked that he’d gone there while he was teaching engineering at the University of Hawaii. They’d done studies to determine what effect saltwater had on mixing concrete for the buildings there, since they made all their precious fresh water with massive evaporation tanks. If the evaporators broke down, there would be serious problems. Finnegan caught on to this and said that if the Japanese knew there were problems with the fresh water evaporators, their listening post on Wake Island would be sure to report it. Rochefort sat there quietly, the permutations of code groups clicking away in his mind as he reached back to the code groups they’d broken. Water, he thought. Midway. AF.
“That’s all right, Joe,” he said to Finnegan. He got up and left. Holmes wouldn’t learn until years later that the thousands of tumblers in Rochefort’s mind clicked in unison at that moment and unlocked the key to proving AF’s identity.
In the succeeding days, they got bits and bobs of tantalizing information. Admiral Chuichi Nagumo would lead the Kido Butai to be in position northwest of AF by N-2 day for the attack on N-day. What was N-day? they wondered. From their many decrypts, they had only three examples of how the Japanese coded dates: three kana characters. This was further encrypted beyond the additives and codes. It was truly a riddle wrapped in a mystery inside an enigma. Rochefort’s group realized that in order to get all the dates to snap into place, they would have to solve this riddle.
While they were working the date-time code, Yamamoto flashed the Combined Fleet’s order of battle—the roster of ships he intended to use—as well as detailed instructions for the campaign against AF and the Aleutians. Finnegan recognized it for what it was straightaway and started to decode it with help from Ham Wright and Joe Rochefort. That left Lasswell with the date-month code.
Amid all the piles of intel, a decrypt came across Tom Dyer’s desk from the Japanese stronghold of Kwajalein:
The AF air unit sent following radio message to commandant 14th Naval district. AK (Pearl Harbor) of 20th. With reference to this unit’s report dated 19th. At present time we have only enough water for two weeks.
Please supply us immediately.
Dyer correctly interpreted that Midway—AF—had sent a plain-language message to Admiral Bloch at Pearl Harbor—AK—thereby giving the Japanese vital information. He snorted and waved the message at Rochefort. “Those stupid bastards on Midway. What do they ever mean by sending out a message like this in plain language?”
Rochefort was uncharacteristically placid about the affair because it was a devious bit of radio intelligence deception he’d played—not only on the Japanese but also on Washington. The ruse wouldn’t be revealed for years, but when Holmes had remembered the water distillers on Midway, and that Finnegan was reading Japanese intelligence reports out of Wake, Rochefort realized that he knew enough of JN-25 to get the Japanese to inadvertently show their hand. There was at that time an underwater cable between Hawaii and Midway for secure communications. He asked for, and received, permission to send a message over the secure line to Midway requesting that they send a plain-language radio broadcast stating that their water distillers had broken. They elaborated by also sending it in a strip-cipher code that was known to have been captured at Wake Island. Bloch kept the deception going by acknowledging receipt and saying that he’d send barges with fresh water. The Japanese were listening, too, of course, wrote a coded report, and sent it out—thereby conclusively confirming that AF was Midway. Rochefort—and likely Bloch, Layton, and Nimitz—kept the secret for years.
For their part, Washington warned Rochefort not to be taken in by Japanese radio deception.
A Tale of Two Subs Page 11
