Authors: Ed Offley
Besides the rotors, designers had added two additional layers of encryption to the Enigma machine. One device was an “alphabet ring” mounted on each rotor and the reflector like a tire on a wheel. The ring displayed the rotor position indicator letters that appeared in small windows on the face of the machine.
Each rotor could thus be turned individually until the letters designated for that day’s use appeared in the Enigma’s faceplate windows and were then locked into a stud. This enabled the Enigma operator to change the rotor circuit for each letter prior to use. Another encryption layer came from a cable plug board on the front of the machine. The plug board had twenty-six electrical sockets corresponding to the alphabet as well. Following another preplanned schedule, the operator would connect specific pairs of letters using a series of short electrical cables with plugs on both ends.
When the Enigma operator typed his message, the electrical impulse from each keystroke traveled from the keyboard through the plug board cables, then moved through the three moving rotors to the reflector, which redirected it back through a different path in rotors and plug board. Thus, when a letter emerged from the rotor system and plug board, its identity had changed from seven to nine times since the radioman had pressed the key.
Nor was that the end of it.
The genius of the encryption system was that in addition to the external inputs, the rotors interacted with each other when the machine was in use. As the operator typed each succeeding letter in the message, the right-hand rotor advanced either one or two letter positions by a ratchet-and-pawl mechanism on its outer edge. The other two movable rotors also advanced, but only after a larger number of keystrokes. In reality, every letter of an Enigma message was encrypted by a unique circuit pathway. In effect, the same letter of the alphabet would encrypt to a different letter each time the operator pressed that key.
For additional security, the navy provided each U-boat with a
Kenngruppenbuch
(recognition group book) containing 17,576
three-letter “trigrams.” The radio operator would select a trigram identifying the specific cipher in use (the German navy assigned separate ciphers to different user groups, such as the Atlantic U-boats, blockade-runners, and so on). Next, the radioman would select a second trigram at random for the message key for that specific message. This identified the starting position of each rotor—the letters appearing in the small windows at the front of the machine. He then added a null letter as the first letter in the cipher indication trigram and a null letter to the end of the three-letter message key. He next wrote both groups on a message form. Finally, he encoded the two four-letter groups using a separate bigram (two-letter) table and wrote them on the form.
The sophistication and complexity of the Enigma were nothing short of staggering. Yet, for all of its extraordinary safeguards, the British by January 1942 were regularly reading the contents of the messages between BdU and the U-boats—incredibly, often within a day of transmission.
3
T
HE EFFORT BY
W
ESTERN GOVERNMENTS
to crack Enigma had begun seven years before the outbreak of the war, when Polish cryptanalyst Marian Rejewski began researching the encryption technology. A brilliant mathematician, Rejewski in 1932 managed through “permutation theory,” a higher algebraic analysis, to unlock the secrets of the Enigma rotor wiring—the heart of the encryption process—for Rotors I through III. In 1938 he had also solved Rotors IV and V, though by then the German navy had distributed three more, Rotors VI to VIII, for use in naval communications. Still, Rejewski’s critical knowledge enabled
the Polish
Biuro Szyfrow
(Cipher Bureau) to build several replica Enigma machines. On the eve of war in July 1939, the Poles gave one of them to the British, who rushed it to a guarded estate fifty miles northwest of London called Bletchley Park, where the newly organized Government Code and Cypher School was scrambling to penetrate German military communications.
In late 1939, the British designed the prototype of what they would call a “bombe,” a fast electromechanical machine duplicating the Enigma wiring design. Entering service in March 1940, the bombe solved the Enigma rotor settings mechanically, which then allowed cryptanalysts to break the messages into clear text. By August 1941, Bletchley Park was decrypting most naval Enigma traffic within thirty-six hours.
After breaking an Enigma message, the cryptanalysts transmitted the clear text via a secure teleprinter line to the British Admiralty’s Operational Intelligence Centre in the underground Citadel in London. There, a small team, led by barrister–turned–Royal Navy volunteer reserve commander Rodger Winn, crosschecked the material against other intelligence for further confirmation. Winn and his staff then passed carefully sanitized intelligence reports to the Admiralty Trade Division and to Western Approaches Command in Liverpool. Using that information, Admiral Percy Noble and his operations staff guided convoys at sea in eluding the wolf packs and warships in hunting them down.
4
By the end of 1941, the staff at Bletchley Park had grown to over 1,500 mathematicians, linguists, cryptanalysts, and clerks, all laboring around the clock. The staff targeted communications from all German bodies—ranging from the Luftwaffe and Wehrmacht to the Schutzstaffel (SS, Defense Corps)—but one
of their highest priorities, given the crucial stakes at hand in the Battle of the Atlantic, remained attacking the encrypted Enigma messages between Admiral Dönitz’s headquarters in Lorient and his U-boats at sea.
Despite Enigma’s presumed inviolability and Kapitänleutnant Feiler’s radio-deception ploy, the British knew exactly what was developing in the North Atlantic during the first eleven days of January 1942. In a “Most Secret” weekly U-boat Situation Report on January 5, Winn wrote,
The U-boat situation has one feature of particular interest: since [December 24] until [January 3] a U-boat has been employed solely to create a fictitious impression in our minds by moving rapidly through the Northwest Approaches [between Scotland and the Faroes] and making signals at short intervals on varied frequencies so as to simulate the presence of a considerable number of U-boats in the area. . . . The object of this ruse is thought to be the concealment of one or all of three actual moves that are developing: (a) a concentration of 6 U-boats off Cape Race, St. John’s and Argentia.
5
Despite the great lengths to which BdU had gone to use U-653 to protect its other U-boat forces in the North Atlantic, the British—thanks to their extensive code-breaking efforts—had seen through the ruse easily and had pinpointed exactly where the true threat lay. Had Dönitz known of the British awareness of U-653, he would have become catatonic—because he would have realized that Enigma was not secure.
Over the next week, Winn and his team also assembled a gradually clearing picture of the westward progress of the
seventeen U-boats heading for Operation Drumbeat and Newfoundland. Even though the five Type IX boats kept their radio transmissions to a minimum, Degen and the other Ziethen boats engaged in regular communication with BdU. By Monday, January 12, Winn had assembled a stark picture of what was unfolding along the eastern coast of Canada and the United States:
The general situation is somewhat clearer and the most striking feature is a heavy concentration [of U-boats] off the North American seaboard from New York to Cape Race [Newfoundland]. Two groups have so far been formed. One, of 6 U-boats, is already in position off Cape Race and St. John’s, and a second, of 5 U-boats, is apparently positioning off the American coast between New York and Portland [Maine]. It is known that these 5 U-boats will reach their attacking areas by 13th January.
6
Understanding procedures established between the British Admiralty and COMINCH Headquarters in Washington eight months earlier, Winn transmitted this information to Admiral Ernest King’s headquarters at Main Navy via a secure line through the Intelligence Section (NID 18) of the Admiralty’s delegation at the British embassy in Washington, DC. Unlike on December 7, when the six aircraft carriers and fourteen escort warships of the Japanese strike force attained total surprise via radio silence and deceptive movement across the northern Pacific, the British on January 12, 1942, provided the US Navy with explicit and accurate warning of an imminent and widespread attack by German U-boats against coastal shipping.
Incredibly, the Americans did nothing—inviting a naval catastrophe that would dwarf the losses at Pearl Harbor.
7
T
HE TORPEDO STRUCK WITHOUT WARNING.
A
T ONE MOMENT
, the British freighter
Cyclops
was heading northeast parallel to the New England shore, pushing through moderate swells that moved from left to right across its bow. The next moment, a thunderous explosion went off on the freighter’s starboard side. Seawater, smoke, and flames cascaded high into the gloomy overcast sky.
It was 1849 hours Eastern War Time (EWT) on Sunday, January 11, 1942, and Operation Drumbeat, Vice Admiral Karl Dönitz’s U-boat assault on American coastal shipping, was underway a day earlier than he had ordered. Master Leslie Webber Kersley, his ninety-six-man crew, seven gunners, and seventy- nine passengers aboard the 9,076-ton
Cyclops
were nearing the home stretch of a 13,485-mile trip from the Far East to the British Isles when U-123, under the command of Kapitänleutnant Reinhard Hardegen, suddenly attacked. The thirty-six-year-old merchantman was carrying 6,905 tons of general cargo its crew had loaded in Hong Kong and Auckland, New Zealand, before crossing the
Pacific and entering the Caribbean through the Panama Canal en route to the British Isles via Nova Scotia. The sudden blast and gaping hole in the starboard side meant that the ship’s monthlong trek from the Far East had come to a sudden and disastrous end just eighteen hours shy of its scheduled arrival in Halifax. As the ship settled quickly by the stern, Kersley ordered passengers and crew to take to the lifeboats.
U-123 had become the first ship in the Drumbeat wolf pack to bring down an Allied ship in coastal waters. Dönitz had told Hardegen and the other U-boat commanders assigned to this first strike against the United States that while they would operate independently along the Canadian and American East Coast, he wanted their attacks to begin simultaneously for maximum psychological impact. He later transmitted an encrypted Morse code message to the Drumbeat U-boats identifying the attack date as January 13 (late in the day on January 12 in the Eastern time zone). While insisting on the simultaneous attack, Dönitz had given his U-boat commanders one exception to the rule: any Allied merchant ship displacing 10,000 tons or more could be attacked no matter the date and location. Hardegen decided to take advantage of this caveat when a ripe target suddenly appeared in his lookouts’ binoculars.
It was a typical move for the twenty-eight-year-old naval officer, who had found his true calling in the U-boat Force. A native of the Hanseatic city of Bremen in northern Germany, Hardegen since childhood had dreamed of a career at sea. At the age of eighteen, he entered the Kriegsmarine as a midshipman candidate. As one of ninety-one members of the Class of 1933 along with Horst Degen, Hardegen sailed on the warship
Karlsruhe
for its around-the-world cruise. Upon receiving his commission, Hardegen found himself assigned to the German naval air force—an organization that, under the dictates of the 1919 Treaty of Versailles that ended World War I, did not officially exist. Hardegen spent four years as a patrol plane pilot before being unceremoniously transferred to the U-boat Force in November 1939. After serving as first watch officer (1WO) on the Type IXB U-124 for two patrols from August to December 1940, during which time the U-boat sank seven Allied merchant ships totaling 30,624 gross registered tons, Hardegen took command of the small Type IID U-147. In one patrol in early 1941, Hardegen sank the 4,811-ton Norwegian freighter
Augvald
. Then, on May 17, 1941, U-boat Force Headquarters assigned Hardegen as the Type IXB U-123’s second commanding officer. Commissioned just a year earlier,
Eins Zwei Drei
(One, Two, Three), as the crew affectionately nicknamed their U-boat, had already conducted four wartime patrols under Kapitänleutnant Karl-Heinz Moehle, sinking sixteen ships totaling 80,730 gross registered tons.
Despite his success as a 1WO on U-124, Hardegen’s brief command of U-147 told this new crew little of his skills as a U-boat commander. Any doubts U-123’s crewmen may have had about their new skipper, however, were quickly assuaged. On his first two patrols with U-123, Hardegen sank six ships for a total of 26,318 gross registered tons.
In this latest victory, Hardegen and his men had conducted a textbook attack against the
Cyclops
. With darkness setting in, Hardegen had ordered U-123 to close within 1,600 yards of the ship. Following standard procedure for a surface torpedo attack,
Oberleutnant zur See Rudolf Hoffmann, Hardegen’s 1WO, had manned the
Uboot-Zieloptik
(UZO), a set of oversized binoculars whose fourteen-inch lenses gave him an incredibly clear image of the target despite the fading evening twilight. Mounted on a swivel post on the bridge, the UZO glasses transmitted the bearing, range, and target angle to a
Vorhaltrechner
—an electromechanical deflection calculator—in the conning tower down below, which in turn fed the correct heading to the target into the gyroscope of the designated G7a torpedo in tube number 3. After announcing the intended depth of the torpedo run—3.5 meters—through a voice tube to the torpedo room, where a torpedo mechanic cranked in the number by hand, the twenty-four-year-old Hoffmann hit the electromagnetic launch button to fire the weapon, calling out, “Release!” Back came an instantaneous reply from the torpedo gang: “Failure!” The firing system had malfunctioned. But four seconds after that, the torpedo mechanic manually fired the torpedo and called up, “Launched!” Ninety-seven seconds later, the G7a detonated against the British merchantman’s hull.