THE CODEBREAKERS

by DAVID KAHN

  You will understand from the foregoing the utterly tragic consequences if the present political debates regarding Pearl Harbor disclose to the enemy, German or Jap, any suspicion of the vital sources of information we possess.

  The Roberts’ report on Pearl Harbor had to have withdrawn from it all reference to this highly secret matter, therefore in portions it necessarily appeared incomplete. The same reason which dictated that course is even more important today because our sources have been greatly elaborated.

  As another example of the delicacy of the situation, some of Donovan’s people (the OSS) without telling us, instituted a secret search of the Japanese Embassy offices in Portugal. As a result the entire military attaché Japanese code all over the world was changed, and though this occurred over a year ago, we have not yet been able to break the new code and have thus lost this invaluable source of information, particularly regarding the European situation.

  A further most serious embarrassment is the fact that the British government is involved concerning its most secret sources of information, regarding which only the Prime Minister, the Chiefs of Staff and a very limited number of other officials have knowledge.

  A recent speech in Congress by Representative Harness would clearly suggest to the Japanese that we have been reading their codes, though Mr. Harness and the American public would probably not draw any such conclusion.

  The conduct of General Eisenhower’s campaign and of all operations in the Pacific are closely related in conception and timing to the information we secretly obtain through these intercepted codes. They contribute greatly to the victory and tremendously to the saving in American lives, both in the conduct of current operations and in looking towards the early termination of the war.

  I am presenting this matter to you in the hope that you will see your way clear to avoid the tragic results with which we are now threatened in the present political campaign.

  Please return this letter by bearer. I will hold it in my most secret file subject to your reference should you so desire.

  Faithfully yours,

  (Sgd) G. C. MARSHALL.

  This extraordinary missive put Dewey in a grave predicament. He felt that the Japanese simply could not be using the same code in September, 1944, as they had been in November, 1941. Profoundly convinced of the Tightness of his cause and of the “dreadful incompetence” of the Democrats, both in the country and the world as a whole and at Pearl Harbor in particular, he—and many Republicans—might well have thought that true patriotism actually called for exposing some three-year-old secret about prewar codes to prove his point and elect the right man and the right party to control the destinies of a whole nation. For with that exposure furnishing apparently solid evidence, the Pearl Harbor charge might have propelled him into the White House. Dewey talked the matter over in detail with Bell and with Herbert Brownell, his two closest advisors. He weighed these arguments and the prize at stake—leadership of the most powerful country in history—against the possibility of prolonging a war in which hundreds of Americans were dying daily and against his regard for Marshall as an utterly truthful and honorable man. After two days of intense deliberation, he decided not to mention the code-breaking.

  Marshall had never actually asked him for any assurances, and Dewey never communicated his decision to the chief of staff. But, Marshall acknowledged, “there seemed to be no further reference to the matter in the campaign.” Dewey lost, heavily. Afterwards, as a gesture of appreciation, Marshall sent Bissell to Albany with copies of the current MAGIC to show Dewey how it was helping in the Pacific. Dewey told Bissell that he had heard that a debate on Pearl Harbor was going to be held in Congress, and he asked whether Marshall wanted him to intervene and suppress it. When Bissell returned, Marshall had him call Dewey and say that Marshall had already embarrassed him with requests which had affected his personal actions and that he would not make any further requests. Dewey replied that it wasn’t a matter of personal embarrassment but of the progress of the war. Bissell told the governor that Marshall had anticipated that reply and still had no request to make. Nevertheless, the debate never materialized. The episode had a final echo at Roosevelt’s funeral, when Dewey was thrown in with Marshall, “I asked him to come to the War Department with me. He did and we showed him the situation out in the Pacific. Showed him also the current magic, giving the Japanese movements at that time, and made as plain as we could to him just what the importance of these matters were. His attitude was very friendly and very gracious.”

  So ended the last and most serious threat to the security of American cryptanalysis. The Japanese never realized the ludicrous transparency of their codes. They never suspected the truth behind the Yamamoto incident. And cryptanalysis went on to play a role in the struggle against Japan even beyond its formal end.

  The cipher war in the Pacific drew to its conclusion not with sagas of high drama but rather with a foam of poignant vignettes. There was, for instance, the time when a junior communicator’s wise-guy thoughtlessness robbed Halsey of the classic gun duel between battleships for which he had always yearned.

  It happened on October 25, 1944, during the Battle for Leyte Gulf. Halsey had organized within his 3rd Fleet a Task Force 34, consisting of most of his battleships and cruisers. Since it stayed with his main force, it was largely a paper organization, but owing to a syntactical ambiguity in a message, Nimitz and others thought it was a separate body. The battle ranged over an enormous area, and while Halsey’s carriers were attacking the four battleships and two carriers of the Japanese Northern Force, Admiral Thomas C. Kinkaid sent, in clear, a desperate call for the gunfire of Task Force 34 ships. While Halsey was speculating over the effect its possible interception by the Japanese might have had, Nimitz, who had been following the battle by radio, sent him a query: “Where is Task Force 34?”

  Naval communication procedure called for the head and the tail of messages—their most vulnerable points—to be concealed by nulls consisting of meaningless words. This “padding” was supposed to be totally alien to the text, but the enciphering ensign in Pearl Harbor violated this rule when he used a phrase that was “just something that popped into my head.” Though he correctly set the padding off from the text by doubled letters, communicators on Halsey’s flagship decided against removing it on the chance that it might be part of the message. Thus, the decipher tape that they rushed to Halsey read:

  From CINCPAC [Nimitz] action Com Third Fleet [Halsey] info Cominch [King] CTF seventy four [Kinkaid] X Where is repeat where is Task Force thirty four RR the world wonders

  When Halsey read this, he said, “I was as stunned as if I had been struck in the face. The paper rattled in my hands. I snatched off my cap, threw it on the deck, and shouted something that I am ashamed to remember…. I was so mad I couldn’t talk.” The more he thought about this apparent insult, the more furious he became, and, a little before 11 a.m., he angrily turned Task Force 34 from due north to due south to go to Kinkaid’s aid. “At that moment,” he said, “the [Japanese] Northern Force, with its two remaining carriers crippled and dead in the water, was exactly 42 miles from the muzzles of my 16-inch guns.” Though the carriers were later finished off, the misunderstanding cleared up, and the enciphering ensign chewed to bits by Nimitz, Halsey had lost “the opportunity I had dreamed of since my days as a cadet.”

  Bitterest of the vignettes depicts a negation of America’s total communications-intelligence mastery near the end of the war—with tragic consequences. At about 3 a.m. on July 30, 1945, the Japanese submarine I-58 encoded a dispatch reporting that three hours earlier it had “released six torpedoes and scored three at battleship of Idaho class … definitely sank it.” He addressed it to 6th Fleet and to Combined Fleet headquarters and transmitted it on a standard Japanese naval frequency.

  Americans intercepted it; FRUPAC read it; and within 13 hours of its transmission had the report in Nimitz’ Advance Headquarters, on Guam. The position given was approximately tha
t of the heavy cruiser Indianapolis, which on July 26 had delivered a chunk of U-235 to Tinian for the first atomic bomb. But nobody at Advance Headquarters checked to see if any American battleships, or cruisers, or other heavy vessels, were missing. Why, nobody knows. As a result of this and other blunders, no search was instituted for the swimming crewmen for nearly a week; in the meanwhile, nearly 900 American sailors died uselessly—the greatest disaster at sea in the history of the United States Navy.

  American cryptanalysts, who usually strove to win battles, worked to make peace when they solved Japanese messages that indicated Japan’s desire to quit the war before the atomic bombs had devastated her and opened the era of nuclear war. Though the formation of a new cabinet in April, 1945, implied a mandate to seek peace, the United States obtained the first concrete evidence of this desire on July 13. On that date, President Truman and other high American officials read an instruction of Foreign Minister Shigenori Togo to his ambassador in Moscow, Naotake Sato. Togo urged Sato to see the Soviet Foreign Minister before the Big Three conference at Potsdam and tell him of the Emperor’s strong desire to end the war. Explain, Togo said, that the only real obstacle to peace was the Allies’ demand for unconditional surrender. If this were insisted upon, he said, Japan would have to continue the fight. The implication was that another surrender formula might bring peace.

  In the next few days additional messages were intercepted and read that threw further light on Japanese intentions. They verified the view of many experts on Japan that a promise to preserve the Emperor would open the way to a surrender which in most other respects would be unconditional. Probably as a result of this cryptanalyzed information, America, Britain, and Russia at Potsdam moderated their demands from an unconditional surrender of all Japan—which would have threatened the throne in which each Japanese rooted his very claim to being Japanese and which Togo had therefore said would be unacceptable—to an unconditional surrender of merely the military. The Big Three hoped to end the war without having to use the atom bomb, but they would do so if necessary. Hence the Potsdam Declaration on July 26 offered Japan a choice between “unconditional surrender of her armed forces” and “prompt and utter destruction.” But Japan, unable to accept the former because it did not positively promise the retention of the Emperor, embraced the latter.

  The fatal glare spread first over Hiroshima. The traffic analysts of the Tokumu Han, who had learned how to predict the B-29 bombing raids launched from Tinian, listed the special signal of the single bomber that preceded Hiroshima’s obliteration. Three days later, they heard the signal again. Japan had no air force to alert, and the analysts could not tell that the plane was heading for Nagasaki. But they knew what the beeps meant. As they mechanically plotted it, they were, in the Japanese phrase, swallowing their tears.

  For Americans, however, MAGIC extended its efforts even beyond the conclusion of hostilities. The United States, fearing a possible banzai suicide resistance by Japanese troops in Korea, like that encountered on some island garrisons, had not planned to occupy the peninsula until September 23, and then only with an entire army corps. But American cryptanalysts disclosed that the Japanese commander there was appealing to his own government to hasten the movement of American troops into Korea. This proved rather conclusively that no adverse reaction need be expected, and so a mere regiment took control of the country on September 3—three weeks early. Similar considerations aided the disarming of Japanese troops in China and Manchuria, and finally expedited the peaceful occupation of the islands of Japan itself.

  What happened to cryptology during World War II?

  The war worked no changes as basic as those of telegraphy, which revolutionized the structure of cryptography, or of radio, which ushered cryptanalysis into the world as a factor of importance. Rather it enlarged, accelerated, intensified what was already there. This held true even in the two most noteworthy cryptologic developments of the war. One was internal, in which the changes were so great as to be qualitative: the evolution in the operations of cryptography and the techniques of cryptanalysis, and one external: the elevation of cryptanalysis from just one among many sources of intelligence to the principal one.

  All this resulted, of course, from the immense increase in the use of radio. Blitzkrieg required the closest coordination between motorized spearheads, air support, and consolidating infantry. Global conflict demanded global communications. Unprecedented volumes of traffic streamed through radio channels. To handle it, huge agencies sprang into being.

  In World War I, the U.S. Army and Navy had about 400 persons in cryptology (excluding cipher clerks), or about one person in every 10,000 under arms. In World War II, there were 16,000 in cryptology—40 times as many—and the ratio was one person in every 800. In World War I, a handful of officers and enlisted men in the Code Compilation Section had produced codes for the whole A.E.F. In World War II, hundreds of privates at Arlington Hall did nothing but draw up key patterns for the tens of thousands of M-209s all over the world which devoured a new pattern once every eight hours. (Eventually, a linguist on the Hall’s think squad devised a mechanism that produced the patterns automatically.) In 1918, a few men had carried the packages of codebooks to the American headquarters that received them. In 1942, Japan was faced with a major logistics task in distributing new code-books to her far-flung forces. Her disastrous pre-Midway failure to do the job in time showed that codes had become cargo almost as essential as food or ammunition. Codes and ciphers cloaked even more secondary forms of messages—meteorological, direction-finding, airplane, merchant ships’. Intercept stations covered the globe. Branches and subsections sprouted that the science had never known: the Signal Security Service had a special section just to distribute its solutions, another one just to improve and develop cryptographic mechanisms. Brass hats abounded. Recruiting drives were mounted. The whole paraphernalia of large organizations materialized. Cryptology became big business.

  At the same time, cryptology completed an evolution in the two core areas of cryptographic operations and cryptanalytic techniques. World War I had left both of them depleted and inadequate. Hand encipherment had barely coped with the message load, even though codes furnished a primitive mechanization. Brute frequency analysis had barely sufficed for the ADFGVX, even though it was handled by a master. The 1920s began to furnish the tools and ideas for which this lack cried out. In cryptography, Vernam, Hebern, Scherbius, Damm, and Hagelin invented practicable cipher machines—secure, portable, rugged, printing. Governments gradually introduced them into service, replacing the old pencil-and-paper methods. In cryptanalysis, Friedman pioneered with statistical methods. Hill opened a window on the new vistas of mathematics. Cryptologic agencies hired mathematicians like Kunze and Kullback and Sinkov as cryptanalysts and purchased tabulating machines to make more calculations. Mathematics generated analytical techniques of great precision and power. These trends, which were still just getting under way in 1939, accelerated with a rush during the war and culminated by 1945. This evolution transformed both cryptography and cryptanalysis and gave each a characteristic it still has. World War II mechanized cryptography and mathematized cryptanalysis.

  This development of cryptology’s substance, like the growth of its administrative organization, was paralleled by the enormous amplification of its effects. In World War I, cryptanalysis played a central role in one event of high significance—the American declaration of war following the Zimmer-mann telegram disclosure. In World War II, cryptanalysis helped make possible at least four critical events—Midway, Yamamoto, the rapid cutting of Japan’s lifeline, the defeat of the U-boats. Cryptanalysis was not just a tangential and merely helpful factor; it was a vital one.

  Indeed, the higher in the politico-military realm are the events, the more important becomes cryptanalysis. At the front, it probably stands equal with prisoner-of-war intelligence or aerial reconnaissance. But neither of these can match it for providing insight into the strategic plans of top general
s or the basic diplomatic policy of a whole country. A spy may occasionally pluck forth a richer nugget, but he cannot refine the quantity of ore that a cryptanalyst can, nor can he command the credibility. The ungrudging tributes of the two German spymasters attest to this superiority: Walter Schellenberg’s acknowledgment that the assistance rendered him by the communications-intelligence chiefs “made most of my success in Secret Service operations possible,” and Wilhelm Höttl’s boast that his Hungarian cryptanalysts provided him with “at least a hundred successes such as seldom fall to the lot of a Secret Service working in the ordinary ways.” General Amè, chief of Italy’s Servizio Informazione Militare, listed three succinct reasons why intelligence chiefs like cryptanalysis: it is usually the cheapest, the latest, and the truest source of information.

  After the war was over, an American official familiar with the wartime value of codebreaking said that it had shortened World War II by a year. The estimate may be conservative: a Japanese victory at Midway would probably have cost the United States more than a year to come back. When asked about the value of the wartime codebreaking, Vice Admiral Walter S. Anderson, a former Director of Naval Intelligence, exclaimed “It won the war!” Hyperbole, to be sure, but indicative nevertheless. In fact, the letter of General Marshall, who was certainly in a position to know, tends to support the hyperbole. It was this vital importance of cryptology that was new in the world. No one could have articulated in 1919 the tribute that Representative Clarence B. Hancock offered at the end of 1945 on the floor of the Congress of the United States: “I believe that our cryptographers [cryptanalysts] … did as much to bring that war to a successful and early conclusion as any other group of men.”

  For in World War II cryptology became a nation’s most important source of secret intelligence.