CHAPTER FIVE
THE WIRELESS WAR of August to December 1914, in the far Atlantic and South Pacific, was the most dramatic intelligence episode of the Great War. Historians of the Eastern Front were later to suggest that Germany’s crushing victory over the Russians at Tannenberg, in east Prussia, in 1914 was brought about by Russian wireless laxity; Rennenkampf and Samsonov, the commanders of the invading Russian First and Second Armies, were accused of transmitting to each other the positions they intended to reach next day en clair (without encoding or enciphering their messages). More detailed research suggests that the Germans were guilty of equal laxity and that the cause in both armies was not carelessness but a lack of trained cipher clerks.1
The course of the campaign of 1914 in the West is not held to have been affected by intelligence failures, since few important messages were sent by wireless; the French, using the Eiffel Tower in Paris as a transmitter, jammed German wireless comprehensively but without discernible effect. During the years of static warfare that followed, neither wireless messaging nor interference played any significant part, since the available equipment was ill-adapted to trench conditions and most communication, both strategic and tactical, was conducted by hand-carried paper, as was traditional, or by telegraph or telephone. Some overhearing, by erratic earth-conduction, was found to be possible, but its use was short-term and tactical at best.
Wireless interception by navies was of greater significance, although both the British Grand Fleet and the German High Seas Fleet became scrupulous at observing wireless silence. The British, ever on the alert for warnings of the Germans “coming out” into the North Sea, garnered every message that they could. On the only occasion, however, when advance warning might have made a difference, the superbitas of the Royal Navy’s traditional officer class robbed the fleet of advantage. The Chief of the Operations Division, Rear-Admiral Thomas Jackson, visited the naval intelligence division in the Admiralty, known as OB 40 (Old Admiralty Building Room 40) on 31 May 1916 to ask where its direction-finders (direction-finding had improved since 1914) placed the German signal DK, call sign of the German High Seas Fleet’s flagship. He was told, correctly, that the location was Wilhelmshaven and departed without explaining his reason for asking. Jackson was the sort of seagoing naval officer who did not share his thoughts with the non-combatant intelligence staff, composed as it was of such lesser beings as naval schoolmasters, university linguists and academic mathematicians. Had he explained why he wanted to know where DK was, he would have been told that the German flagship left its call sign at home when proceeding to sea, to disguise its movements, and adopted another. On the basis of his half-clever question, Jackson therefore telegraphed Jellicoe, commander of the Grand Fleet at Scapa Flow, to assure him that the High Seas Fleet was still in harbour. As a result, Jellicoe eventually heard that the Germans were “out” from Beatty, commander of his battlecruisers, which had been sailed south on other information. He was then at sea himself, but making less than best speed in order to conserve fuel, so that he was late meeting the enemy battleships off Jutland, late fighting the battle and late cutting off their retreat. Admiral Jackson’s disinclination to take the codebreakers into his confidence robbed the Grand Fleet of a major opportunity to scupper the German navy for good.2
Jackson was exceptionally arrogant. A Royal Naval Volunteer Reserve lieutenant, W. F. Clarke, belonging to the OB 40 staff, recorded that he “displayed supreme contempt for [our] work. He never came into the room during [my] time there except on two or three occasions, on one of which he came to complain that one of the locked boxes in which the information was sent him had cut his hand, and on another to say, at a time when the Germans had introduced a new codebook, ‘Thank God I shan’t have any more of that damned stuff.’ “3 There were many like Jackson, however, if not so bad, and it would take nearly a generation to pass before operations officers would begin to accept that most “raw” intelligence was only as good as the interpretation put on it, often best supplied by the intelligence officers who gathered it on a day-to-day basis.
OB 40 also had its admirers, and rightly so. It began to supply crucial information almost from the start, including forewarning of the raid on the English east coast towns of Scarborough, Hartlepool and Whitby on 16 December 1914.4 Had it not been for a visual signalling error committed by Beatty’s flag lieutenant—who was to repeat his mistake on three later occasions, at Jutland with disastrous effect—the Scarborough raid might have resulted in the destruction of the German battlecruiser force.5 OB 40 had only then been in existence since 8 November and had been brought into being because of an intelligence windfall. In late October the Russians had delivered to the British a copy of the main German naval codebook (SKM) and a collection of square-ruled charts, used to denote sea areas. They had been recovered from Magdeburg, a German light cruiser lost in the Baltic on 26 August. OB 40 subsequently acquired the codebook used for communication between German merchant and naval ships (HVB), found in a German steamer interned in Australia early in the war. Finally, it got possession of a codebook used by German senior officers (VB), allegedly dredged up in the nets of a British trawler off Holland on 30 November, at a spot where four German torpedo boats had been sunk on 17 October.6
It was with this material, and intercepts collected via a hastily established chain of coastal listening stations, that OB 40 went to work. They were aided by the Germans’ very free use of wireless—forced upon them in part by the dragging up of their oceanic cables by the British cable ship Telconia on 4 August 1914—but above all by the nature of the means the Germans used to disguise their signals.
Secret writing takes two forms, known to cryptologists respectively as codes and ciphers. Cipher is a method hiding meaning by altering the form language takes, either by “transposition” or “substitution.” Transposition, a technique so ancient that there is no record of its origins, works by changing the order of letters; the simplest system, familiar to any cipher-minded schoolboy, is to shift once along in the alphabet, so that A becomes B, B becomes C and so forth. “The cat sat on the mat” is thereby recorded as “UIF DBU TBU PO UIF NBU”; the result is unlikely to baffle an interceptor for any length of time. There are many ways of complicating a message in transposition cipher; one of the simplest is to run the letter group together—UIFDBUTBUPOUIFNBU—to disguise the word length, but it provides little protection. Another, more sophisticated, is to shift two or three or ten letters along in the alphabet; while straight transposition underlies the ciphering, however, the iron laws of “frequency analysis” will yield the solver a way in. The law of frequency reveals that, in English, E is the most commonly written letter, followed by A and so on. Frequency tables, known to all cryptologists, provide a ready means of decipherment. Frequencies are different in other languages—Z, rare in English, is common in Polish—but the tables cannot be defeated.
Not, that is, unless complexities are introduced. Cryptographers—those who write ciphers or codes—have devised many complexities. Perhaps the best known, and most difficult, is the alphabetical grid, which arranges the twenty-six letters of the Roman alphabet (reduced to twenty-five by combining the letters I and J) in a square five letters wide and five deep, and numbers the columns. If A is the first letter in the top left-hand corner, it is rendered as figures 11, and so on to Z as 55. At its most elaborate, known as a Vigenère, after its sixteenth-century French inventor, the square is twenty-six by twenty-six, presenting a frequency problem of great difficulty. It is not insurmountable, though it was long thought to be so.7
Further complications may be devised, particularly when cryptographers begin to use figures rather than letters in transposition. There developed, during the seventeenth century, a strange halfway house between transposition and its cipher alternative, substitution, in which, for example, King Louis XIV’s principal cryptographers, the Rossignols father and son, rendered whole words into mathematical figures. The technique had been anticipated by numbering common French “digraphs,” e.g., QU, OU, DE, but the Rossignol system, known as the Great Cipher, defeated everyone; it was only unlocked, long after the meaning of the messages in which it was written had ceased to have importance, at the end of the nineteenth century.
By then, however, cryptologists were on the brink of instituting a new cipher system altogether, employing full-scale mathematical “substitution” for letters. Mathematical substitution appeared to promise true impenetrability since by addition or subtraction, a numerical message could be so varied that a cryptanalyst—who attacks secret writing—would simply be defeated by time; but as long as the intended recipient possessed the “key” to understanding the chosen mathematics, it could be read at the other end.
Keys were the problem: how to ensure that senders and recipients possessed the same set, how to deny keys to the enemy? The simplest solution was to write the keys in a book, logically arranged, which could be owned by all legitimate parties. Codebooks were widely in use during the eighteenth century, if only to disguise the more important words in a message, for example, the proper names of people, places, ships and so forth, the rest being left in plain language. Major Benjamin Tallmadge, George Washington’s chief of intelligence after 1778, devised a codebook out of Entick’s Spelling Dictionary by taking from it the most frequently used words, numbering them in alphabetical or numerical order and adding random words for those not listed. He also chose sixteen numbers for key individuals and thirty-six others for cities or places. Tallmadge kept the original, sent another copy elsewhere and the third to George Washington. It cannot have disguised much from the British if a letter of 15 August 1779 is a fair sample: “Dqpeu [Jonas] beyocpu [Hawking] agreeable to 28 [an appointment] met 723 [Culper Jun.] not far from 727 [New York] and received a 356 [letter].”8
This amateurish example discloses the principal weakness of a codebook: that, by collecting the words used, from messages intercepted, parts of the book can be reconstructed; if enough material passes through the hands of the enemy, it can be reconstructed in its entirety.
An apparent safeguard is to avoid the use of the alphabet altogether and employ only figures, singly or in groups. By the beginning of the nineteenth century the British were doing just that. A message from William Drummond, British emissary to Denmark, to the Foreign Secretary, Lord Grenville, in 1801, on the eve of the Battle of Copenhagen reads, in its last sentence, “3749 2253 529 2360 1268 2201 3356,” which stands for “Count Bernstorff does not even affect to conceal his alarm and inquietude.”9 The protection, however, is not as great as seems, even though, in the original, there is no indication of sentence length, nor do the groups betray word length. But by painstaking accumulation, again, watching for repetitions, and by guesswork, the codebook can be reconstructed and meanings deduced.
From the use of all-figure codes, it was but a short step to a much more secure system, technically known as “super-encipherment.” It employed two—or more—keys: the codebook itself and a system of figure alteration, by addition or subtraction. Since the groups thus altered did not coincide with those in the book, and did not obviously repeat themselves, retrieval of meaning became much more difficult. Yet not impossible: there was an underlying logic, supplied by the second key, which might be established by mathematical analysis. German diplomatic telegrams were, during the First World War, commonly super-enciphered. Oddly the most famous, the Zimmermann telegram, was not. Broken by Room 40, its contents—which encouraged Mexico to attack the United States—prompted President Wilson’s declaration of war on Germany.
Many other methods of complexifying secret writing had been devised by the beginning of the twentieth century, many of them variations on the Vigenère square. The most ingenious was invented by an American army officer, Major Joseph Mauborgne, in 1918. It came to be known as the “one-time pad” and was indeed unbreakable. A Vigenère square was constructed in two copies, one held by the sender, one the receiver. It gave the key to the enciphered message; once used by both parties, it was destroyed. One-time pads protected messages absolutely because the coincidence between cipher and plain text was entirely random and the absence of repetition, assured by destruction, forbade all chance of frequency analysis, or any other method favoured by cryptanalysts.
The one-time pad suffered, however, from a disabling defect. To be useful, pads had to be distributed on a very large scale and had to be identified, so that sender and recipient knew that they were working on the same document. The generation of random numbers on a large scale is not a simple matter either; deliberate attempts to randomise will inadvertently follow patterns, the more conspicuously the greater the pace and volume of output, while large-scale distribution in real time poses insurmountable logistic difficulties. Any persuasive solution to the problem of randomising and distribution was, therefore, likely to be enthusiastically welcomed in military circles everywhere.