The Bletchley Park Codebreakers (15 page)

Nevertheless, losing no time, Dr Divita brought the Admiral in charge of naval history to see me and when I held the message headed
SUPERMARINA
in my hand it seemed as if time had stood still and I was nineteen again and wearing a green jumper. I spotted the word
incrociatore
, the Italian for ‘cruiser’, for which we had a chart and remembered that it was a new recruit, Phillida Cross, who had found the clinching click with a lovely starfish and earned herself an honourable mention in Dilly’s poem. The Admiral would have been amazed that a starfish could have sunk a cruiser if I had been able to tell him so. Margaret Rock and I had been able to rod out enough of the rest of the message to ensure that we had the right wheel position. It had been raining all day and was still pelting when I rushed it over to the machine room. Dilly was rung up at home and came in to take charge of any further messages and the ‘girls’ on duty went thankfully home to bed. Cynthia was finally put to bed too; no seduction and no codebooks but just hard cryptographic slogging and a lucky break, or as Dilly put it in his epitaph on Matapan to Mussolini:

My new Admiral friend drank the health of ‘Dilly and his girls’, just as Admiral Cunningham had done in the Cottage forty years before. On his return to
Supermarina
, the Admiral wrote a charming letter of thanks, but, with the lesson of Cynthia still in mind, he ended on a cautious note: ‘Hoping to be given the opportunity of meeting you again, on work matters.’

There has been a tendency of late to relegate Dillwyn Knox to the status of an old-time professor who did brilliant work on ciphers in Room 40 but was defeated by Enigma, the credit for the breaking of
which must go entirely to Turing and Welchman. It is to be hoped that this book will go some way to redressing the balance and that when Bletchley Park’s restoration plan goes ahead, the Cottage will be dedicated to his memory. ‘Nobby Clarke’, an old friend of Dilly’s since Room 40 days, who was in overall command of the naval section at Bletchley Park at the time of Matapan, summed up the situation when he added a verse to Dilly’s Matapan poem.

7

A BIOGRAPHICAL FRAGMENT: 1942–5

JOHN CHADWICK

In May 1942, I was an Able Seaman serving on board HMS
Coventry
, an anti-aircraft cruiser attached to the Eastern Mediterranean Fleet based in Alexandria. I had been trying in various ways to improve my position, and one of the things I had done was to acquire a reasonable
degree of competence in speaking modern Greek. This was a much rarer accomplishment than it is today. I was therefore not unduly surprised when on putting into Alexandria after a long absence I received orders to go ashore and report to an office in the naval base called COIS. No one told me what those letters stood for, but since it bore some resemblance to the Arabic word for ‘good', I took it for a favourable omen. When I found the place, I discovered that it stood for ‘Chief of the Intelligence Staff'. To my astonishment I was interviewed by the COIS himself (Captain Bousfield, RN), who had with him a middle-aged English civilian. I assumed he was there to test my knowledge of Greek.

But I was puzzled by the questions I was asked. They seemed quite uninterested in my linguistic ability and Greek was never mentioned; they concentrated on my schooling and my first year as an undergraduate at Cambridge. I had abandoned my course in Classics to join up after the fall of France in 1940. I was even more perplexed when I was asked to demonstrate my ability to write small numerals clearly. However, after a short delay I was given to understand I had passed the test, whatever it was, and I was sent back to my ship with orders for my immediate transfer to HMS
Nile
, the naval base.

Two days later I reported for work (at the absurdly late hour of 0900) and was directed to another office, where I met the head of the section I was to join. He had apparently been absent when I was interviewed. His name was Commander ‘Jock' Murray, RN. As I learned later, he had had as his confidential clerk an English lady who was the wife of the Fleet Engineer Officer. Murray was well known for his violent temper, and he had been sufficiently provoked to call this lady a liar, whereupon she had walked out. It occurred to the COIS that if he had a rating as his clerk, he could call him any name he chose without creating another incident.

He gave me a long lecture on security, and explained that I must keep what I was doing secret from my messmates, not an easy thing on the lower deck. When he was satisfied I had grasped its importance, he calmly told me that his section was trying to decipher Italian naval signals. ‘You say you know Latin,' he remarked, ‘so you shouldn't have much difficulty with Italian.' He then produced a large pile of old intercepts, an Italian code-book (the
Cifrario Mengarini
) and some recipherment tables. He demonstrated how to use them and left me to decode the remainder. After making a few
mistakes I soon learned how to do this, although of course I could not understand all the telegraphic Italian that emerged. There was no sort of Italian dictionary in the office, not even the unilingual one we later acquired.

After a few days I was initiated into the art of indexing (hence the need for small numerals), building a ‘depth' and eventually reconstructing the recipherment key. This was of course much more interesting and I soon picked up enough Italian to follow what was coming out. But before I had gone very far, the news from the Western Desert became alarming; the British forces had been driven out of Cyrenaica and Rommel was invading Egypt. The Army announced its intention of holding him at a place no one had ever heard of, called El Alamein. The Navy promptly ordered the evacuation of Alexandria, and overnight not only did the fleet sail, but all the auxiliary and depot ships too; we awoke next morning to find the harbour empty except for a single minesweeper.

There were two civilians working for the Commander, the one I had met at my interview, W. Stanley Backhouse, and a lady, Pauline Smith, who was the wife of an army officer. At this stage I had no idea what their duties were. When the panic started we were ordered to pack up our work in sacks labelled with innocuous tags like ‘Baccy' meaning Backhouse, and to stand by to move at a moment's notice. Next day the order came to destroy all confidential documents, so the sacks were unpacked again and I helped incinerate thousands of intercepts and indexes made from them. I quite expected to be abandoned to take part in the defence of the naval base while my superiors got away, but in fact I was ordered to accompany them on a journey by train to Cairo. We were taken to Heliopolis Museum, the main outpost of Bletchley Park in the Middle East. My arrival created administrative chaos, since I was a lone naval rating attached to an Army Intelligence Corps unit, itself attached to an RAF station. There was no work to do, but we had not long to wait before we were moved again. We had the impression that the German Air Force were aware of our location; one night they dropped a stick of bombs which straddled the building, fortunately with little damage.

The ‘I' Corps unit to which I had been attached received orders to leave and took me with them; we travelled by train to Ismailia on the Suez Canal, were ferried across, and then began a most uncomfortable journey in a train of covered goods wagons across the Eastern Desert.
When we reached Gaza, in what was then called Palestine, we were taken to a tented camp. Conditions there were quite tolerable since it was summer, though we had nothing to do; and in little more than a fortnight we repeated the journey in reverse, but this time in slightly more comfort. From Cairo I was sent back to Alexandria by train.

The unit now reassembled and had to start afresh with only the latest intercepts to work on, together with the information stored in the memories of the workers. We were also disrupted by the move of the naval base to new quarters in a suburb of Alexandria, about five miles to the east. A luxurious villa (the Villa Laurens) was taken over for the main HQ, and various adjacent buildings were included in a secure perimeter for offices. We were allocated a small bungalow. We had not been there long before Commander Murray announced that he was leaving, for what reason I never learned. Mr Backhouse was left in charge and proved a much easier person to work for. He had, before the war, been a shipping agent in Naples, so he spoke the language fluently and I learned a lot from him. Our duties were now reorganized, and I became his assistant, working mainly on a low-grade code we all called ‘Ouzo', although the name was a risky allusion to its Italian name,
Cifrario per Uso di Mare
. I was to spend a long time on this, so it may be worth describing in some detail.

The signals sent in this code were easily recognizable, since each group consisted of a letter and three figures. The letter normally stood at the beginning of the group, but occasionally occupied other positions. Mr Backhouse had worked on it for some time before the evacuation and established that it was un-reciphered, but cleverly designed to make penetration difficult without a very large amount of traffic. It was divided into twelve sections or ‘pages', each of which was indicated by the letter in the group; there were two letters for each page, to be varied arbitrarily, and from time to time these were shuffled. This change caused us little trouble, once we had grasped the procedure.

On each ‘page', each word in the book was supplied with ten three-figure code groups, one beginning with each digit from 9, 8, 7, and so on to 0. Thus in theory the encoder had a choice of twenty code groups for each word, but since it was easy to pair the letters, in practice we had ten codes to break simultaneously. We were able to reconstruct the arrangement of the columns of figures on the page, since, human nature being what it is, the 900 column was the one most
frequently used, and the frequency of each column fell off regularly as the columns stood further and further away from the list of words. Only the 000 column showed a slight rise in frequency.

This now became my chief task, and Mr Backhouse left me more and more to myself, though he constantly checked and verified my work. What I found difficult to believe was that a book so regularly constructed would have ten decode sections on each page, since the various groups for each word appeared to be randomly selected within the hundred possibilities. I suggested therefore that the book was in fact so constructed that it would be easy to find where on the page each numerical group might be located, so that there would be no separate section for decoding. But Mr Backhouse would not hear of this.

My first success was to work out that each ‘page' had the numbers divided into two classes. Those of the first class always preceded those of the second, so that each ‘page' represented a double-page spread. All the groups on the left-hand side and all on the right shared a common feature. On the left-hand pages the first and last digits of every group were both odd or both even; on the right-hand pages, if the first digit was odd, the last was even, and if the first was even, the last was odd. The rule could be expressed by saying that if the sum of the first and last digit of a group was even, it belonged on the left-hand page; if odd, on the right-hand page.

This suggested that the arrangement of the numbers in each column, now of fifty, not a hundred groups, was also methodical. We had established the value of enough groups in the 900, 800 and 700 columns to be able to see the numerical connections between the groups with the same meanings in different columns. By this means I discovered that there were only three arbitrary factors to be worked out for each column: the starting point, whether the next group was that following in ascending or descending order, and a break point somewhere in the columns. Thus if the 900 column began with 939, the group for the next line would be either 941 or 937. The sequence then continued until it reached 999 or 901 or the breakpoint occurred. If the break came at 963, the next group would be either 999 and continue descending to 997, 995, etc.; or it would be 901 followed by 903, 905, etc.: