A Tale of Two Subs

by Jonathan J. McCullough

  9

  The Silent Service

  At Station Hypo, the summer and fall brought in few decrypts.The leak leading to the Chicago Tribune story suggesting a break in the Japanese codes caused consternation through-out the Navy. Especially incensed were the Redman brothers, who encouraged prosecution of the parties involved. When it seemed that a sensational public trial would air all of the Navy’s most precious secrets, the anti-Roosevelt publisher of the Tribune needed no further incitement to make a big stink. As the case drew nearer, the government’s seriousness in pursuing criminal charges seemed to confirm that they had actually broken the code. Finally, cooler heads prevailed and the case was dropped. The Japanese intelligence apparatus in neutral countries probably read of the developments with interest, however, because after only three months in service, JN-25 was hastily changed in August.

  Hypo had to drop all work on the old version and start yet again. Fortunately, the sudden expansion of the unwieldy Japanese empire created problems in codebook distribution. Many ships and far-flung installations across the Pacific didn’t receive new codebooks in time, but still needed to be informed about fleet movements and receive instructions and orders. As a result, duplicate messages were sent in the new JN-25, the previous version of JN-25, and other minor codes for a few weeks, offering the code breakers a Rosetta stone of sorts that gave brief glimpses into JN-25’s latest iteration.

  For Hypo, there was never a good time for the Japanese navy to make a radical change in JN-25, but the August changeover was particularly ill-timed due to the Marine landings at Guadalcanal and Tulagi on August 7. Two days later, a Japanese task force surprised the American landing force. Without benefit of advance warning provided by radio intelligence, the Allies were no match for Japan’s superior ships, and suffered a humiliating defeat at the battle of Savo Island. The Australian heavy cruiser HMAS Canberra sank, with 193 lives lost. The U.S. cruisers Vincennes, Astoria, and Quincy also went down, each having a complement of 800 to 900 men. The marines on Guadalcanal were now as effectively isolated on the island as their Japanese counterparts, and the battle would rage for several excruciating months as each side sought to reinforce and resupply their troops. The fighting at sea was no less savage than on the island itself, and during the several naval battles that ensued, dozens of ships sank. So many went down in the channel between the islands around Guadalcanal that it became known as Ironbottom Sound. The men at Hypo felt anguish at each loss, and despite the extraordinarily complex and labor-intensive task of cracking JN-25, they took each sinking as evidence of personal and professional failure. Many of the officers in the sunken ships were classmates and friends from the Naval Academy, dead and gone forever.

  At about this time, Rochefort’s intransigent enemies in Washington spun plots to remove and humiliate him. First they sent officials to send back scathing reports about his suitability for command using an illegal code under Nimitz’s nose. When Nimitz discovered that messages had been going back and forth under his command and without his knowledge he was furious, but the code went inexplicably missing and he was left in the dark. The powers that were also denied Rochefort any acknowledgment for his contribution in cracking JN-25 in time for Midway. When his replacement arrived and he was assigned for temporary duty in Washington, he could see the writing on the wall. Nimitz was confronted by a fait accompli when notice that Rochefort’s temporary duty was now permanent came by mail, conveniently arriving too late for Nimitz to protest to the Bureau of Personnel. Frustrated by the command in Washington, Rochefort’s irascible temperament reared up and he requested sea duty. In yet another breathtaking example of convenient self-contradiction, the bureaucratic conspiracy of dunces shamelessly backtracked to opine that what Rochefort knew was too valuable to put him in a command where he might be captured. Rochefort, the oracle of Midway, ended up in charge of a floating dry dock in San Francisco.

  In one of his last communications to Jasper Holmes, Rochefort asked that he and Hypo give as much loyalty to their new boss as they had given to Rochefort. Though the surprise appointment of a new boss and the doldrums associated with their struggle to crack the new version of JN-25 were demoralizing, Dyer, Finnegan, Lasswell, Wright, and the rest met the challenge with equanimity and, if anything, worked harder than before. The nature of the war was changing, and the organization of Hypo in relation to the other pieces of the intelligence puzzle was changing, too.

  Offensive operations like Guadalcanal required a much larger and broader intelligence apparatus across all services, and Holmes’s Combat Intelligence Center—the desk Rochefort had used to hide the activities of Hypo—mushroomed into a bewildering number of acronyms, as well as an infusion of men and resources. The Joint Chiefs of Staff were drawing up plans to roll back Japan’s defense structure of island rings, and these plans required not only radio intelligence but also photo reconnaissance and interpretation, prisoner interrogation, and rapid translation of captured documents. After an unfortunate incident where a friendly ship struck a mine outside one of the Allies’ bases, the new Joint Intelligence Center, Pacific Ocean Area (JICPOA), even got the task of gathering and distributing intelligence about American bases as well as Japanese strongholds.

  Despite the need for intelligence from all sources, radio intelligence still represented the best opportunity to determine the Japanese navy’s strength, composition, and distribution. While the cryptographers worked to regain their footing on the new JN-25, they were still able to read the Truk port director’s messages dispatching ships into and out of that important fortress. Early in 1943—despite a warning from OP-20-G in Washington that it was impossible—Hypo was also able to crack what would become known as the Maru Code. Like JN-25, it was a superenciphered code, but had only four digits instead of five, making it much less complicated. It revealed the comings and goings of Japan’s merchant marine: the Maru-class cargo ships bringing iron, tin, rubber, and other war matériel to the homeland, as well as the invaluable oil tankers and military supply ships that kept Japanese outposts stocked and fed.

  The Maru Code was obviously most useful to the submariners, the only ships in the Navy that could sneak into enemy-held waters and sink the Marus that fed the Japanese war machine. Along with decrypts of Japanese sailors’ messages telling of submarine sightings, torpedo attacks, and detection of American submarines by DF—direction finding—Holmes started serving up the exact location and noontime positions of important convoys. When Admiral Lockwood became Commander Submarines, Pacific (ComSubPac), he brought on Sailfish skipper Dick Voge as his chief of staff. Voge came to Holmes every morning to go over the decrypts relevant to the submariners and brought a thin Pacific overlay map to update information about the location and direction of enemy convoys as well as the location of his own subs. Since the submarine skippers generally preferred to maintain radio silence so as not to give away their position to the Japanese, sometimes Holmes’s Japanese eyewitness accounts were the only clues as to the submarines’ locations.

  Voge got high marks for his administration of submarine business at Pearl Harbor. On the nightly “fox” broadcast to submariners,* he often included small personal remarks, such as the announcement of sailors’ new babies. For the first time, someone who’d actually seen the undersea war had their backs, and the submariners felt that someone actually cared about them while on patrol.

  One of the first things they’d noticed—long before Dick Voge came on the scene—was that the skippers’ war damage estimates were often inflated. In fact, Hypo had determined that the carrier Dick Voge sank in the Sailfish was an important ship—a seaplane tender—but not a carrier as they’d hoped. There were many other letdowns for other skippers, but it was best to have an accurate account of the enemy’s strength. Another discovery was that the Japanese convoy escorts often claimed that they’d sunk a submarine after a perfunctory counterattack. This happened so often that in the aggregate the Japanese high command had the idea that more American submarines w
ere sunk than actually participated in the war. Unfortunately for the Japanese, they didn’t have decryption to verify these sinkings, and while their antisubmarine tactics were terrifying and even sometimes effective, the false reports and the old initial victory disease misled them into not making improvements until a serious gaffe was made by a high-ranking U.S. politician.

  Perhaps the most unsettling discovery was the steadily accumulating evidence that even after Lockwood had settled the dispute about torpedoes running too deep, the Japanese radio transmissions were now confirming the submarine skippers’ long-suffering observation that the detonators were blowing up prematurely or not at all. In an odd mirror image of the victory disease afflicting the Japanese navy, the Bureau of Ordnance and their representatives at the sub bases continued to blame the skippers for the dud torpedoes and refused to consider for a moment that the Mk VI detonator was anything less than a paradigm of perfection. But contrary evidence was mounting. The Japanese noted the prematures, thus alerting them to the presence of American submarines, as well as the heart-attack-inducing sight of ghostly torpedo wakes running toward their ships, then under them, then harmlessly past them. The Japanese broadcast all of these contact reports on the radio, secure in the knowledge that it was absolutely safe to do so.

  The submariners, Hypo, and perhaps especially the Japanese were able to acknowledge that the Mk VI exploder didn’t work. Everyone except the Bureau of Ordnance and its apologists on the sub bases knew. Holmes was finally able to confirm it personally when in late January 1943, the Australian corvette Kiwi used sonar to acquire the Japanese submarine I-1 as a target off the coast of Guadalcanal. The Kiwi proceeded to lay down depth charges that exploded underneath the submarine; the rapidly expanding gases displaced the water ballast in the sub’s tanks, upset its compensation, and heaved it violently up to the surface. The Kiwi then set upon its prey, methodically ramming the stranded sub three times and shooting the men popping out of the hatches. When the sub captain made a courageous but ill-fated samurai sword attack on the corvette, he was shot down. The I-1 ran aground but sank by the stern, and in the confusion of the gathering night, several of the Japanese submariners made a daring escape to Japanese-held lines, taking with them valuable intelligence documents.

  They didn’t secure all of the documents, however. Salvagers were able to secure an original copy of the JN-25 code, and although it was out of date and Hypo had already cracked most of it, Holmes would write that the discovery was for the code breakers “as precious as moon rock to an astronomer.” They were able to confirm old hunches, correct long-standing errors, and glean seldom-used code groups they’d never been able to crack. In addition to this was a codebook listing all the two- and three-digit codes signifying geographical areas, including confirmation of their old favorite, AF for Midway. The Aussies were also able to take the wounded navigation officer as a prisoner for interrogation back at Pearl. Despite the animosity of war, Holmes was able to sympathize with him as he recounted his experience on the doomed sub. Having reached a certain rapport with the officer, submariner-to-submariner, Holmes asked the question he’d wanted to ask most: Were the Japanese having trouble with their torpedoes?

  The officer answered in Japanese and smiled while a translator told Holmes the answer.

  “No,” he said. “But you are.”

  That confirmation and the rest of the intelligence materials came at a steep price. The crew of the I-1 who were able to get away reported the possible loss of some of the codebooks. Although they buried or destroyed some of the books, they couldn’t recover them and couldn’t account for what was left on the submarine. The Japanese realized they had a major security breach on their hands and tried desperately to scuttle the I-1—the bow was still sticking grotesquely out of the water near the beach—but the Allies beat back the ships sent to sink the submarine. Two weeks after the I-1 went down, the Japanese navy went through the laborious process of changing their codebooks once again, but as there were no fewer than 200,000 copies scattered throughout the Pacific theater, they had to transmit signals in new codes for those who had received new codebooks, and then retransmit them for those who had not. The result was a headache for security and even more openings for the code breakers to attack the Japanese codes. Within a month of the code change, Hypo was able to read enough traffic in the new codes to produce actionable intelligence.

  One of the most important breaks in the war came on April 13, when Alva Lasswell came across a short message with huge consequences. It was Admiral Yamamoto’s itinerary for a personal inspection of bases around Bougainville, near Guadalcanal, where Japanese forces were gearing up for a major aerial offensive against the Americans. Holmes and Lasswell took the decrypt to Nimitz’s intelligence chief, Ed Layton. Yamamoto had spent time in the United States before the war attending the Naval Academy and Harvard University, as well as a posting as a naval attaché in Washington, D.C. Several high-ranking Navy officers remembered him well. His dossier probably included the information that Yamamoto was exceedingly punctual in his appointments. The question was whether they should intercept Yamamoto’s plane and shoot it down. Brilliant tactician though he was, Yamamoto was becoming a familiar adversary, and knowledge of this particular enemy’s capable imagination and his inspired use of carrier-based planes was an asset in itself. But in the end, Yamamoto’s abilities outweighed Nimitz’s appreciation of those abilities, and Nimitz concluded that even if Yamamoto’s replacement was a devil they didn’t know, the great Japanese admiral’s death would be a debilitating blow to the Combined Fleet’s morale. What they proposed was nothing less than an attempt at assassination that might not work, and that had the added possibility of tipping off the Japanese about Hypo’s success. Nimitz went up the chain of command all the way to President Roosevelt, who weighed the evidence and concluded that the benefits of having Yamamoto out of the picture outweighed the risks.

  Nimitz coordinated a plan with Admiral Halsey and the Army air commander on Guadalcanal, and on April 18, a group of long-range P-38 Lightning fighters shot down the plane carrying the admiral of the Japanese Combined Fleet, Isoroku Yamamoto.

  Yamamoto’s chief of staff, Captain Yasuji Watanabe, was beside himself with anger and frustration, not only because of the admiral’s death, but also because radio operators did not carry out his explicit orders to transmit the admiral’s itinerary using only JN-25. He was convinced that the army’s code was compromised, and that the American code breakers read the army version of the itinerary. Nor were the Japanese the only ones who were furious. British prime minister Winston Churchill instantly surmised what had happened and was reportedly filled with righteous fury that his great friend FDR had risked everything on a gambit to “get Yamamoto.” If this was how FDR would treat the Japanese code, what blunder might he commit that would jeopardize Enigma’s secrets? Though finely barbed, Churchill’s concerns were legitimate, and only time would tell.

  The Americans waited with waning patience for the Japanese to announce Yamamoto’s death, which they finally did more than a month after the plane had gone down. There was a minor scandal during the interim when everybody seemed to know that the intelligence came from radio decryption. High-ranking officers tamped down the rumors by spreading a cover story that coast watchers had seen Yamamoto get into a plane. Miraculously and despite widespread distribution, the true story remained a secret to the Japanese. Concealing ULTRA’s secret was worth dying for, and the Navy had once again narrowly averted disastrous consequences. With the next gaffe they would not be so lucky.

  In June 1943, Andrew J. May, the powerful chair of the House Committee on Military Affairs, returned from a fact-gathering tour of American military bases, including Pearl Harbor. May was an enthusiastic war supporter—the country was nearly unanimous in this conviction—but his blustery, rah-rah bombast and the important committee soapbox he used to express it often rankled even the most ardent war supporters. In one typically unlikely fantasy, at the height of th
e war he called on the Navy to “steam into Tokyo harbor and blow the city to bits.” For him, the Japanese were not a capable, tenacious, and formidable enemy, but racially inferior, stupid yellow “Jap” bastards. To illustrate how stupid they were, in a fit of braggadocio, he claimed to reporters that the Japanese couldn’t touch U.S. subs because they didn’t set the depth charges deep enough. The story hit the wires and received distribution far and wide, including the local Hawaiian newspapers.

  The Japanese are by no means stupid; the effect of May’s blunder was immediate. U.S. subs reported devastating depth charge attacks as the Japanese organized effective convoys and set their depth charges lower than 150 feet. Many subs’ final reports came in the form of Japanese radio decrypts, when the waters of the Pacific closed in on them from all sides, a ghastly oil slick marking the location where all souls aboard had gone on eternal patrol. The entire Navy was outraged, none more so than Admiral Lockwood, who wrote, “Congressman May . . . would be pleased to know that the Japs set ’em deeper now.” Although he would never atone for the many ships and hundreds of men his indiscretion may have lost, years later May was convicted of taking bribes in connection with his powerful post as chairman of the Military Affairs Committee.