THE CODEBREAKERS

by DAVID KAHN

  German Army cryptanalysts solved American M-209 messages almost from the days late in 1942 when the two armies first clashed in North Africa. They picked up such tidbits of information as that the 72nd, 45th, and 29th Light and the 71st Heavy Anti-Aircraft Regiments were placed under the 52nd Anti-Aircraft Brigade, which is part of the order-of-battle intelligence basic to a field commander, that on April 1, 1943, the 3rd Infantry Regiment was located at grid square 43835, or 37 kilometers from Gafa, that American forces were forbidden to fire upon airplanes unless the airplanes attacked them (to prevent shooting down Allied planes). All these details were fitted together to give the German command a picture of the troops facing them, their state of mind, their preparation.

  Occasionally, a single solved message produced strikingly dramatic results. During a conference at the headquarters of the Commanding General, Southwest, in 1943, Colonel Karl-Albert Mügge, commander of Fernmeldeaufklärung 7, brought Field Marshal Kesselring a British intercept that had just been crypt analyzed. It reported that in North Africa several troop columns were caught in a traffic jam of their own making by crowding into a wadi at—and here the cryptogram was garbled so that the exact location could not be read. Kesselring called for an immediate air search; the jammed wadi was discovered while the Germans were still in conference. Kesselring promptly ordered an air attack, which wreaked considerable destruction upon the concentrated British forces.

  Early in February, 1944, during the Italian campaign, the American 5th Army attempted to recapture the Carrocetto factory, a pivotal point which the Germans had taken in a counterattack. “It was important for VI Corps not only to regain the Factory area but also to effect the relief of at least a major part of the I Division,” the 5th Army historian wrote. “Aided by the 191st Tank Battalion, men of the 1st Battalion made their way into the Factory in the afternoon, only to be driven out. Though our artillery and tanks converted the buildings into a blazing mass of ruins, the enemy held; prisoners reported that an intercepted radio message had given them foreknowledge of the attack. Another attack before dawn on the 12th likewise failed, and the 45th Division gave up the effort to regain the Factory.”

  As the Allies gained air superiority and the Germans could no longer reconnoiter by air, they depended more and more on radio intelligence. This was especially true after the Normandy invasion. But this means was not omniscient. In the fall of 1944, when General George Patton’s army was preparing to bite out the fortress of Metz, the German forces detected his preparations, largely through radio. “Yet,” wrote a German staff officer, “the actual attack on 8 November came as a surprise to the front line troops.”

  In the field, the German Army’s communication intelligence unit worked closely with the Luftwaffe’s Funkaufklärungsdienst (“Radio Reconnaissance Service”). This was the intelligence side of the Air Force’s Nachrichten-Verbindungswesen, or N.-V.W. (“Intelligence and Signal System”), whose chief served on the staff of the O.K.L. He also prescribed secret communications systems for the Luftwaffe. Air-to-air communications, which were mostly by voice, employed simple codewords to disguise unit names, much as American pilots referred to one another as EASY RED or GREEN ARROW in the style made familiar by war movies. Air-ground communications were encoded in small three-digit or three-letter codes. Luftwaffe ground-to-ground cryptography used the Enigma.

  The Funkaufklärungsdienst employed more than 10,000 men. Its largest subdivision was Luftnachrichten (“Air Intelligence”) Regiment 351, with 4,500 men, which intercepted, solved, and evaluated the radio traffic of Allied light and heavy bombers, fighters, transports, and air staffs in Western Europe. An additional unit of 1,000 provided further detailed information on the heavy bombers. Smaller regiments covered other theaters. Luftnachrichten Battalion 350, with 800 men, served as the Luftwaffe center for basic cryptanalysis and traffic analysis, as well as for the study of new enemy radars and radio navigation systems to find the best means of jamming or deceiving them. It also covered the Allied transatlantic air transport service. It was attached to the main headquarters of the Funkaufklärungsdienst.

  A three-letter code of the Luftwaffe, used in 1945

  Other cryptanalysts served in outlying Funkaufklärungsdienst units, solving messages in systems whose basic solution had been worked out at headquarters. They had reportedly tried to use women in teams for solving a widely used Allied air-ground system, called SYKO, but switched to male students when the women did not produce satisfactory results. They tested the youths by crossword puzzles and sent the 10 per cent doing the best to a training school for about a month. Here they were trained in SYKO cryptanalysis and nothing else. As an incentive, the Nazis told the trainees that the lower 90 per cent of the class would be shipped off to the Russian front.

  Training card for Allied air-ground cipher SYKO

  Early in the war, SYKO consisted of 30 unrelated, mixed cipher alphabets printed on a card. The alphabets were to be used in succession to encipher a message, the encipherer using an indicator to define the one he was using first. The cards were changed every midnight. Later, SYKO took the form of a hinged frame holding a card on which 32 mixed alphabets of letters and numbers were printed vertically. The frame also supported 32 sliding strips, each also with a mixed alphabet, each of which uncovered and covered one of the card alphabets as it moved up and down. The encipherer slid the strips to align the plaintext message on them horizontally at the foot of the frame, and read the ciphertext from the letters of the card showing immediately above the tops of the strips. The alphabets were reciprocal, so that decipherment followed the same procedure. It produced the same cipher as the older version: a periodic polyalphabetic with mixed alphabets, whose period, moreover, was known—rather like the Für GOD of World War I. An e in the first column was always represented by the same ciphertext letter while that card remained in use, which was for 24 hours. The Allies apparently used SYKO because it was light, fast, and simple, but its insecurity meant that on days of heavy traffic the Axis SYKO teams were reading Allied air messages by 10 or 11 a.m.

  It was probably not SYKO that enciphered the message that gave the Funkaufklärungsdienst one of its greatest triumphs, since the message originated in a high-echelon ground command and was directed to other ground commands, while the planes themselves maintained radio silence. These were 178 four-engined Liberators, heading for the Rumanian oil fields at Ploesti, Hitler’s chief source of oil for his thirsty war machine, in one of the longest-range and potentially one of the most important air strikes of the war. As they lumbered into the air at Bengazi on the morning of August 1, 1943, for their 1,200-mile flight, the 9th Air Force spread a short message to Allied forces in the Mediterranean area announcing that a large mission was airborne from Libya. This was necessary because only a few weeks before, in the invasion of Sicily, the U.S. Navy had shot down dozens of American troop planes in the tragically mistaken belief that they were German bombers.

  The message was picked up by a Funkaufklärungsdienst unit recently posted near Athens. Soon its cryptanalysts had reduced it to plaintext. Lieutenant Christian Ochsenschlager then passed to all defense commands “interested or affected” a message stating that a large formation of four-engined bombers, believed to be Liberators, had been taking off since early morning in the Bengazi area. This gave the antiaircraft defenses at Ploesti, the heaviest in Europe, plenty of time to get ready. When the bombers roared at derrick-top height over the Rumanian oil field, with its wells, refineries, and tanks, they were met with the worst flak encountered by American bombers during the war. Of the 178, 53, or almost every third plane, were downed, and dozens of Americans died.

  The German cryptanalytic agency that probably had the greatest effect upon the course of the war was also the smallest and least known. It belonged to the O.K.M., and Grand Admiral Karl Dönitz, commander of the German Navy during the latter half of the war, called it his “B-Dienst,” for “Beobach-tung-Dienst” (“Observation Service”). The B-Dienst had lit
tle contact with the other codebreaking agencies. Yet its successes were more far-reaching than any of theirs, and it participated in some of the most unusual activities of the cryptanalytic war.

  Stung in the 1920s by revelations of Room 40’s readings of German naval traffic, the O.K.M. built up so effective a cryptanalytic unit that by the start of World War II the B-Dienst had solved some of the most secret Admiralty codes and ciphers. The penetration of British naval messages enabled German surface raiders to elude the British Home Fleet, spared German heavy ships from many a chance encounter with stronger British forces, permitted surprise attacks on British warships, and helped sink six British submarines in the Skagerrak area between June and August of 1940.

  Perhaps its greatest feat came in the Norway invasion. On March 1, Hitler approved the plan to invade Norway, but set no date for it. Soon thereafter, the B-Dienst solved British naval messages that revealed a British plan to mine the entrance to Narvik, far in the north of Norway, and to occupy that port; Britain intended to block German ore shipments. This information enabled the German high command to shape a strategy for surmounting the greatest difficulty in its Norway invasion: how to move its weakly guarded transports from Germany to Norway without interference by the powerful British fleet. When the British Narvik expedition was under way, the high command plotted, Germany would send out a decoy force which the British would think was heading to attack their expedition at Narvik. To protect it, Britain would send the rest of its naval forces away to the north. As soon as this happened, the transports would cross the Skagerrak without fear of major sea attack.

  The scheme worked to perfection. Late in March the B-Dienst showed British vessels en route to Narvik. On April 2 Hitler set the invasion for the 9th. The decoy force put out to sea and was spotted on the 7th by the British. As the Germans expected, the Admiralty ordered the Home Fleet and the 1st and 2nd Cruiser Squadrons to head for Narvik. As they raced away from where the action was, the German transports completed their voyage undisturbed by the nation that supposedly rules the waves and landed their occupation troops without a hitch. Even Winston Churchill admitted that Germany had “completely outwitted” Britannia.

  The B-Dienst may have gained a great deal of help from some spectacular coups by the German merchant raider Atlantis. This specially fitted high-speed freighter, whose heavy armament was carefully camouflaged, was one of several that cruised the oceans and harassed Allied shipping. On July 10, 1940, in one of her first actions, Atlantis fired a few shots into City of Baghdad in the Indian Ocean and captured the vessel almost intact when her crew hastily abandoned ship. A boarding party reached the officers’ cabins just in time to point a pistol at the captain and stop him from throwing overboard most of the ship’s secret papers. Among them was the Allied Merchant Ships’ Code, a two-part code issued by the Admiralty for messages via the Broadcasting for Allied Merchant Ships, or BAMS, commonly called the “BAMS code.”

  Also recovered were several superencipherment tables, though not the current ones. Atlantis, however, had aboard in her special crew a wireless operator named Wesemann who had served for three years in one of the German cryptanalytic services. Wesemann achieved what might be the first nautical cryptanalysis on record when, on the basis of the captured code and several merchant messages that he had intercepted, he succeeded in reconstructing about one third of the superencipherment table then in use. As a result, Atlantis could read much of the Allied merchantmen’s traffic and could await her victims at likely spots.

  When the tables were changed, Wesemann partially reconstructed the new ones with the help of some messages found in the wastebasket of the radio shack of another captured vessel, Benarty. The work was completed for him by the B-Dienst, which deduced from his radio queries that he had obtained the BAMS code and consequently sent him the interpretations he needed. Since Atlantis and Berlin were then almost at antipodes from one another, this must rank as the longest-distance cryptanalytic collaboration known. A few months later, on November 11, 1940, the crew of the German raider found aboard Automedon, the 13th ship she had sunk, another copy of the BAMS code and superencipherment tables 7, 8, and 9. All the cryptanalyzed information contributed to Atlantis’ record as the war’s deadliest sea raider.

  She may have sent the B-Dienst photographs of the captured codebooks when one of her prize ships returned to Germany, or the B-Dienst may have obtained a copy elsewhere. Either way, the German knowledge of merchant messages vastly improved U-boat attacks. And, wrote Churchill, “The Battle of the Atlantic was the dominating factor all through the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea, or in the air, depended ultimately upon its outcome.” More than once, the B-Dienst placed in the hands of the U-boat commanders the knowledge that brought them to the edge of victory.

  In 1941, for example, the B-Dienst read messages to convoys from the Commander in Chief, Western Approaches, that directed those convoys from the danger zones just west of the British Isles. With this intelligence, the U-boat command had no difficulty in deploying its submarines to the maximum effectiveness. Allied losses mounted steeply. In March, April, and May, U-boats sank 142 vessels, or more than one every 16 hours. In January and February of 1943, the B-Dienst mastered British naval cryptosystems so fully that it was even reading the British “U-Boat Situation Report,” which was regularly broadcast to the commanders of convoys at sea, telling them the known and presumed locations of U-boats! “These ‘Situation Reports’ were of the greatest value to us in our efforts to determine how the enemy was able to find out about our U-boat dispositions and with what degree of accuracy he did so,” wrote Admiral Dönitz.

  Page of decoding section of British BAMS merchant ships’ code

  The following month, March of 1943, saw the climax of the Battle of the Atlantic. And the climactic action, the greatest triumph of the U-boats, in which they very nearly severed Britain’s lifeline, stemmed directly from a series of B-Dienst solutions.

  The first came on March 9. A B-Dienst report gave the precise location of the eastbound convoy HX 228. (The HX stood for Halifax, Nova Scotia, assembly point for all fast convoys. Slow convoys, which started at Sydney, Cape Breton Island, Nova Scotia, were designated SC.) Shortly thereafter, the B-Dienst reported that the next fast convoy, HX 229, was southeast of Cape Race, steaming on a course of 89 degrees. On the 14th, another solution revealed that a third convoy, SC 122, had received orders at noon the day before that on reaching a given point it was to steer 67 degrees. The U-boats, then operating in wolf packs of two or three dozen, were ordered to search for the convoys. On the morning of March 16, they sighted a convoy which turned out to be HX 229, and in the next two days, 38 U-boats sent 13 ships to the bottom. Meanwhile, HX 229 overtook the slow-moving SC 122, forming a large mass of shipping in a small space of ocean. The wolf pack nipped at its edges and sank eight more vessels, making a total of 141,000 tons sunk in the three-day battle, at a cost of only a single U-boat. Dönitz exulted: “It was the greatest success that we had so far scored against a convoy.”

  The Admiralty despaired. They considered abandoning the convoy system as ineffective, which was tantamount to an admission of defeat, since no alternative existed, the loss rate of single vessels being double that of ships in convoy. “The Germans never came so near to disrupting communications between the New World and the Old as in the first twenty days of March, 1943,” the naval staff later recorded. It marked the darkest hour of the longest, most crucial battle of the war. And in large measure German cryptanalysts had cast this pall upon Britain by—paradoxically—throwing light upon British communications.

  Italy relied for her communication intelligence upon her Army and her Navy. The Navy’s cryptanalysts formed the B section of the Servizio Informazione Segreto, or naval intelligence. Early in 1942, they had penetrated the British naval ciphers in the Mediterranean—these were so poor that Admiral Sir Andrew Cunningham reportedly threatened after the invasion of
Crete to transmit entirely in clear if he were not given better ciphers. The Italian solution of a British scout plane report enabled the Italian high command to warn one of its task-force commanders at 6 p.m. March 27, just before the Battle of Cape Matapan, that the English had sighted him soon after he had put to sea. Next day the reading of an order to Cunningham from Alexandria made the Italians certain that British torpedo planes would attack. They did, and so prepared were the Italians that the intensity of their antiaircraft defense made it almost impossible for the English to identify their targets or observe the results of the attack.

  The Italian Army’s security and intelligence organization, the Servizio Informazione Militare, or S.I.M., had a large and well-organized cryptologic section which solved diplomatic as well as military cryptograms. This was its Sezione 5, headed by General Vittorio Gamba, an old Alpine warrior with austere features. A long-time student of cryptology and author of an excellent article on the subject in the Enciclopedia Italiana, Gamba was a noted linguist who reputedly knew 25 languages. He came to public attention in 1911 when he translated a series of proclamations into Arabic during the Italo-Turkish conflict over Tripoli. The 50 members of Sezione 5 were housed in a large apartment house in Rome far from S.I.M. headquarters but connected by teletypewriter with it and with the extensive intercept unit, Sezione 6, located on the Forte Bocea, a hill behind the Vatican. Gamba’s cryptanalysts maintained close liaison with the chemical section, which worked with secret inks and other means of steganography, with the censorship section, and with the phototypographic section, which rapidly reproduced stolen documents.