The Man Who Broke Napoleon's Codes

by Mark Urban

  As for Soult, he should have known better. Lieutenant-General Hill’s victory in October, smashing a French division at Arroyo de Molinos, had been a disgrace. Berthier must tell him: ‘it is unfortunate that, with an army of 80,000 men they could not make the dispositions which prudence demanded to avoid being beaten by a troop of 6,000 English’. And Soult also needed to know that ‘the great object at this juncture is to take Valencia’.

  The emperor, having set his schemes in train in mid-November, decided to let his brother Joseph know about them on 13 December. He, too, would probably be worrying about the effect all this might have on the Portuguese frontier. So Berthier informed Joseph, ‘it is probable that the English will not undertake anything from now until the month of February, and there is reason to believe they will remain on the defensive’. The emperor had become fixated with Valencia and his confidence was complete that the English would not emerge early from their winter quarters.

  What did Joseph make of all this? Once again, he had taken offence at his brother’s high-handedness. Now he had a confidant in the palace with whom to commiserate. Marshal Jean Baptiste Jourdan had arrived in Madrid in September. Initially he was simply referred to as the governor of that Iberian city, but had also been sent out to act as the king’s military adviser. This one detail of May’s Rambouillet agreement had at least been honoured. Jourdan was no youngster. He had been a soldier when Marmont was born, even fighting in far-off America back in 1781. He had earned the lasting gratitude of many in Revolutionary France as the commander of the army that saved the country from being overrun by invaders in 1794 at the battle of Fleurus.

  He may have been old and tired, but Jourdan, a small, rotund cannonball of a man, still had a wise head on his shoulders. He had also, during his previous service in Spain, learned how to give Joseph military advice in a tactful and friendly manner. The news of his arrival in Madrid, however, excited all kinds of resentment in the headquarters of those commanding armies in the various corners of Spain. Men like Soult, Marmont, Dorsenne and Suchet viewed one another with suspicion at the best of times. Wellington had already learned of such feelings in General Regnaud’s table-talk at Frenada and in the letter from Marmont to Foy that had been deciphered at HQ. Somehow, these senior French officers had managed to sublimate these feelings in the common good during the second half of 1811. Jourdan’s arrival seemed to take the number of marshals in Iberia towards some sort of unstable mass, turning this volatile assembly of ambitious men more and more into open rivals. The effect had been compounded by the angry tone of Napoleon’s orders of late November and early December. Every field commander aspired only to remain high in the esteem of his imperial master in Paris, but they knew that Joseph had been militating for a greater role and that the emperor was likely to launch his Russian campaign soon, thus removing himself from day-to-day superintendence of Iberian matters. For a Soult or Marmont, anxious to increase his wealth or perhaps even secure the throne of some vassal kingdom, the emergence of this partnership between Jourdan and Joseph in Madrid was most unsettling.

  As Jourdan began organizing a proper military headquarters to serve Joseph, the issue of securing his high-level dispatches had at last been settled. The cabinet of Hugues Maret, Napoleon’s chief fixer in Paris, had at last furnished the king and his marshal with a Great Cipher. During the last days of 1811, this had been circulated to all of the most senior leaders. There would be no repeat of the farcical episode of the previous summer: the field commanders, Joseph in Madrid and Marshal Berthier in Paris would all have the right codes to begin secret communication.

  *

  Each user of Joseph’s new grand chiffre would have two tables: one for enciphering, the other for deciphering. The basis of this new code was one of the 1750 ciphering tables printed up by de Puisieulx for the Bourbon foreign ministry. The enciphering table arranged words, syllables, phrases or letters alphabetically. A began with four different ways of writing the letter on its own and then continued:

  Abs … 273

  abaisse, ment … 1179

  abandon, ne … 1035

  abdique, action … 565

  able, s … 185, 808

  abord, e, age … 316

  absolu, e, ment … 1157

  ae … 1162

  In this way, the ciphering table set out the numbers to be used as the staff officer or confidential secretary turned his master’s prose into secret writing. The table used the same coding number for different cases or genders and allowed many options for breaking words down into syllables or bigrams (two-letter groups).

  At the receiving end, the person deciphering would use the other table, one in which the codes were listed in numeric order, each followed by its meaning. The deciphering table was drawn up with a grid of columns and horizontal lines. Looking from the top left corner, the first column ran from 1 to 100, the second across started at 101, going down to 200, and so on. The horizontal lines separated the code numbers into groups of ten. It was all meant to aid rapid deciphering.

  The code table sent to Madrid had 1,200 code numbers, most of which were already filled out. As a ready-to-use diplomatic cipher, it therefore contained many words that were irrelevant to military operations in Spain: 490 stood for Stockholm, 837 for the Crimea and so on. Additionally, Joseph’s officers could soon see that many standard words and phrases needed for waging war in the Peninsula were not included in this cipher. Rather than spelling them out laboriously, they decided to add to the standard 1750 table, increasing the coding numbers by 200 to a total of 1,400.

  The use of a 1,400-number cipher by the French marked an enormous advance. Napoleon’s army was the best organized and most scientifically perfected the world had ever known. Even so, it had never before used ciphers of more than 200 characters for military operations (Imperial diplomacy was another matter). That the new cipher would make life much harder for someone who had cracked the Army of Portugal’s 150-figure code is obvious. The grand chiffre allowed many permutations in the writing of any simple phrase or even of any single word. Taking the example of Seville, it could be encoded as: 1359, the single-letter code given to this city in the modified table; 173.90.1085.711.1118.521.439, when made up of single-letter codes (and there were many different variations possible using different single-letter codes); 189.1071, using the codes for ‘se’ and ‘ville’; or 1181.1085.631.929, a mixture of bigrams, or two-letter codes, with a single-letter one: it breaks down into 1181 [se] 1085 [v] 631 [il] 929 [le].

  The different approaches could be mixed up and the astute user could encode a recurring word in his dispatch differently each time. The cipher retained a few vacant numbers that could be put into the middle of a word to make code-breaking guesswork even harder.

  In short, the design made it extremely hard to deduce anything from the length of a coded passage or the numbers used to encipher it. Even if the person using it made a mistake as crass as the one in General Montbrun’s letter of August 1811 to the governor of Ciudad Rodrigo (mixing code and en clair‡ in an obvious reference to ‘H. E. Marshal the Duke of Ragusa’) it would be far less damaging in this new cipher than it had been in the Army of Portugal one. For whereas that mistake had revealed twenty-one code numbers in a 150-figure cipher, the same phrase in Joseph’s grand chiffre would only compromise one or two out of 1,400 numbers. It was a code of such strength that Napoleon considered it safe to send letters about matters of the utmost importance in the hands of some local peasant. Such a messenger would rarely arouse suspicion, and if he proved to be a traitor and delivered his precious missive to the enemy, nothing would be lost.

  In sending out the tables, Marshal Berthier urged recipients to keep the secret tables in their private papers and only to allow a trusted individual of their retinue to learn about their workings. There were also instructions sent with the ciphering tables that added one or two tricks of the trade that might help an inexperienced cipher secretary. The most cunning read, ‘when finishing the ciphering by the
code that marks the end, add a certain number of vacant codes of your choice after it’. This anticipated that a decipherer might well attack the end of a letter first, since there were standard forms of signing off, such as ‘be assured, sir, of my highest esteem and consideration’. Clearly, anyone trying to crack the code this way would be wasting their time on meaningless code numbers. Once put into action, King Joseph’s new code marked a great step forward in the security of communications. It applied to the military sphere those lessons that had been learned during the evolution of diplomatic ciphers during the previous two centuries.

  *

  Napoleon’s orders to Marmont to march men to the south-east in support of the Valencian operation arrived in several instalments in early and mid-December 1811. They were not protected by the grand chiffre, but this was academic since it seems that none of these critical dispatches were intercepted. One by one, French battalions began breaking camp and forming into their constituent regiments. Then they began tramping down to La Mancha, where a force of two infantry divisions and one of cavalry (9,000 troops or thereabouts) was being formed up.

  These French movements were detected by spies. Guides carrying their scribbled notes came clattering into Frenada’s little square, tethered their exhausted mounts and delivered each morsel of information to the door of Wellington’s Headquarters. The first really reliable report had arrived on 24 December. One of the southernmost divisions of the Army of Portugal had moved out of its usual cantonments and away from the Portuguese frontier.

  In Frenada and the other villages of the border country, British troops sat down to their Christmas dinners. For many, the preferred bill of fare was one of lean roast beef followed by plum pudding. Others opted for a roast goose or game birds. Good claret flowed freely, and the low-ceilinged Portuguese farmhouses were crowded with ruddy-cheeked officers loudly singing festive choruses while inwardly reflecting on the loved ones they had left behind in Old England. Few had any notion of how soon they would be ejected from their warm havens and marched into battle once more. Even Captain Edward Cocks, the dashing but serious-minded officer of the 16th Light Dragoons who occasionally dined at Wellington’s table, could foresee only boredom when he wrote home to his brother on the last day of 1811, asking for more reading matter to be sent out. Cocks wanted Ferguson’s Lectures, Rousseau’s Nouvelle Eloïse and some military texts; he predicted, ‘if we have a dull campaign next year as we had last I shall have time to read through the Bodleian Library’.

  Only in the little two-storey house in Frenada where Wellington and his Staff plotted the latest French troop movements were there intimations that some great project might soon be afoot. In the last days of December, two significant bits of intelligence were received. Firstly, the Army of the North had sent most of its Imperial Guard troops back towards France; Napoleon had ordered them homewards, preparatory to his Russian campaign. Secondly, the concentration of the Army of Portugal’s Valencian expedition was completed. They began marching away from the Portuguese frontier on 29 December. Another of Marmont’s divisions, under General Bonnet, had gone north to assist in the operations against the guerrilla chiefs Mina and Longa (also in accordance with the emperor’s orders).

  As the news of this general eastward movement was charted in Frenada, Wellington conferred with his chief engineer and Quartermaster-General. The view in Headquarters was that they needed at least twenty-four days to encircle Ciudad Rodrigo, batter breaches in its walls with heavy guns and storm the place. The British commander knew he could bring most of his troops into action from their cantonments along the border in just two or three days. Leaning across his maps and plotting the marches of Marmont’s divisions towards Valencia with a pair of dividers, he waited for them to get far enough away to guarantee him that working time.

  On the first day of 1812, Wellington decided that his operation to seize the border fortress was feasible. He knew it would be several days before Marmont even realized what was happening, by which time a good proportion of his force would have marched too far away to alter the issue. The QMG’s department drew up detailed orders and dispatch riders flew to the Army’s divisions, setting them in motion.

  The Light Division started first, with the mission of putting a close blockade around the fortress. ‘During this march,’ one of its young officers recorded, ‘a tremendous storm of sleet and snow took place. The snow froze and adhered to the horses’ hooves, forming balls which raised them several inches from the ground.’ The soldiers of this force then forded the Agueda in this freezing weather and marched around the town in a great encircling movement. Further upstream, heavy wagons and guns began crossing a specially built bridge and by 8 January the fortress and its 2,000 defenders were surrounded.

  Major Scovell and some of the other Staff did not initially leave Frenada. There, a most curious piece of intelligence had arrived. It was a French communication ciphered with the most complex-looking code they had ever seen. Wellington reported to one of his colleagues, ‘I enclose an intercepted letter which we have not been able to decipher.’ Nobody knew at this stage whether this message was a curiosity or the beginning of some important new code. An attack on this fortress of a code would in any case have to wait while everyone’s attentions were focused on Ciudad Rodrigo.

  Any good engineer could see that the best means to approach Rodrigo was from a hill called the Great Tesson, less than half a mile from its defences. The French had hoped that this high ground could be denied to their enemy’s heavy guns firstly by the river Agueda and then by the existence of a small fort they had erected on top of it. An improvised bridge had taken care of the river, and an assault by picked men of the Light Division dealt with the little redoubt atop the Tesson on 8 January. Once this was achieved, they could start using their guns and working towards the points of the fortress walls they intended to attack.

  That night, the infantrymen had worked away feverishly in the darkness with picks and shovels. Theirs was a race against the sinking moon, since their trench would certainly be bombarded by the city’s defenders at first light. This first parallel, 600 yards long, was completed handsomely, with a four-foot rampart of earth-filled gabions by the time dawn came. With daybreak, a furious artillery battle was joined. The French tried to batter down the parallel trench and prevent the British putting their siege guns into it. The attackers used their cannon to try to neutralize the defenders and then begin the process of battering holes in the defensive walls.

  At night, the British troops hacked away, advancing a new trench towards the city. It was cold, dirty work, the men often standing up to their knees in muddy water. It was also extremely dangerous. The French began using two heavy mortars to try to kill the men digging their way forward. These weapons fired a great explosive shell high into the air. If its fuse was cut to just the right length, it would explode ten or twenty feet above the diggers, cutting them to pieces with shards of metal. The British troops soon christened these mortars Big Tom and Little Tom. When they heard the distinctive boom of a heavy mortar, a keen-eyed man would scan the night sky for sight of the fizzing fuse burning away on the shell, and his shouted warning would send the others diving into the mud. ‘Now was a time to cure a skulker or teach a man to work for his life,’ wrote one private of the 95th Rifles who was engaged in this grim work. ‘We stuck to our work like devils, sometimes pitching ourselves on our bellies to avoid … being purged with grape or canister.’

  The French governor knew it was vital to get word to Marmont that he was under attack, since the British move had come as a grim surprise to all of them. A Spanish collaborator was able to slip out of the fortress with an urgent message concealed in his clothing. Patrols of Don Julian’s guerrillas were so frequent that it took him days to reach Salamanca. It was not until 14 January that word reached Marmont himself in Valladolid. Little did the French know it, but as he issued his orders for an immediate concentration of French forces, matters were already moving towards their critical
stage in the borderlands.

  The progress of Wellington’s excavations was such that one week after operations had begun, on 15 January, a second parallel had been thrown up much closer to the walls; about 200 yards from them, to be exact, on a small ridge called the Little Tesson. This new trench was close enough to allow the siege guns to begin their work smashing Rodrigo’s defensive fortifications. With one battery installed in this position and four more firing from the higher ridge behind them, the town’s defences began to crumble. All day long the booming report of one of the twenty-six siege guns was followed moments later by the crump of a heavy ball hitting flagstones at the base of the walls. For the unfortunate French conscripts, this hail of roundshot marked the hours until their situation would become hopeless. They could feel each tremor under their feet as a twenty-four-pound ball struck home and chipped a little more of their security away.

  By 19 January, the Royal Artillery had opened two breaches in the wall. The larger of the two was only 200 yards from the second parallel and it was a gap about 30 feet wide. Not only had the topography of the Tesson ridges favoured this point, by allowing the guns to fire down at the base of the wall, but the harsh curve of the defences made it very difficult for the French to enfilade any infantry attacking it. A lesser breach had been made about 200 yards to the east of this great gap. It was important to attack such a target at several points at once in order to make sure the defenders were unable to concentrate effectively at any one location.

  At dusk on the 19th, men of five British assault columns moved into position. The air was thick with trepidation, for no task was more dangerous than the storm of a breach. One sergeant watching the stormers walking down towards the second parallel pitied them, knowing their task was ‘the worst a soldier can undertake, for scarcely anything but death looks him in the face’. The defenders would have piles of loaded muskets stacked and ready to fire, as well as grenades, mines and other devices to cut down as many of the stormers as they could. All the same, most of the soldiers embarking on this horrific duty were volunteers. In the spirited Light Division, twice as many had offered themselves than were needed. Each man, officer and private alike, sought to beat the odds and by mounting the breach first, distinguish himself in the eyes of his generals. Their gamble was a desperate one, but if they succeeded and survived, a mention in dispatches by Wellington would bring promotion to a young captain and perhaps even an officer’s commission for a ranker. Such was the spirit and ambition of these men. Watching them shuffling forward, other men shouted encouragement. A ration of spirits was broken out and a band played a tune recognizable to them all as the ‘Storm of Paris’. As they crouched behind gabions waiting for the signal, with musket balls cracking and whining overhead, many offered up a prayer. General Craufurd spoke to his men, exhorting them: ‘Soldiers! the eyes of your country are upon you. Be steady, be cool, be firm in the assault.’