Seventy Years Ago This Month at Bletchley Park

January 1942

A Bad Month for the Reputation of Great Britain.

The month has started well for the United Kingdom in the Western Desert as the Africa Corps slips away back to Rommel’s chosen holding line at El Agheila on the Gulf of Sirte. The Eighth Army had hardly distinguished itself during Operation Crusader and an air of cynical wariness has settled on the Desert Army. They know that they have been out-fought by a smaller army with much better tanks and guns and that it is only Rommel’s lack of supplies that has enabled the British to advance once more across Cyrenaica. The great hopes of throwing the Germans and Italians out of North Africa with which the campaign had been launched have not been realised. If only they could be led by some great general, like… er…well, Rommel.  But at home it looks like a victory and at least the capture of Benghazi on Christmas Day serves to soften the blow of the loss of Hong Kong, the first part of Britain’s Far Eastern Empire to fall to the Japanese.  But by the end of the month Rommel has pounced in his opportunistic way and the Eight Army finds itself on the way back to near where it had started at Gazala and Tobruk. The news from the Far East is unexpectedly bleak with the much under-rated Japanese seizing island after island in quick succession. In Malaya things are going no better with our forces making numerous short stands only to fall back down the Peninsula.  But at least there is Singapore behind them; perhaps, the bemused people of Britain thought, this is all a stratagem to lure the Japanese on to defeat? Our great fortress of Singapore will be able to hold out until we can get the reinforcements there – won’t it?

The only good news is from Russia where Stalin on 7th January has launched his armies on to the offensive all along the huge line. At first good progress is made in various places, but the British people hardly notice. Their Government certainly does, and begins to make plans for an alternative landing on the mainland of Europe to that in preparation for the coast of Morocco and Algeria, just in case the Russian victories lead to a sudden collapse of the German armies.  After all, it had happened to Napoleon, as Stalin and Churchill are well aware. But so is Hitler, who is now personally in command of operations, sacking any general who falls back, and throwing all his immense will-power into holding the line at any cost.  Across the Atlantic President Roosevelt has given his New Year statement to Congress, demanding funds to build 45,000 aircraft, 45,000 tanks, half a million machine guns, etc., but in Britain the Americans are known to be great exaggerators and no-one believes they will soon match, let alone easily out strip even these immense figures.  Churchill has been in Washington conferring with Roosevelt at the Arcadia Conference, and the United Nations Declaration is signed by 26 nations.  If the British people are hardly enthused, perhaps that is because they recognise that of the 26 nations who signed, nine South American nations do not seem to count for much in the battle against the Germans and the Japanese, and a further eight are in no position to do anything for their peoples are living under German occupation.

The Breaking of the Luftwaffe Keys. 

 In Whitehall a war rages over the control of Bletchley Park. But it is at BP that occur the two events of that tragic month that might have restored the British reputation if only the world could have been told. In a feat that demonstrates the almost complete mastery that they have now achieved over the Luftwaffe Enigma cyphers, Hut 6 at BP breaks four new Luftwaffe Enigma keys on the 1st January 1942, the very first day the Germans introduce them to service, and continues to read them until the end of the war.  Pink is intended to be the highest Luftwaffe Enigma command cypher, but most highly secret traffic continues to go by Red, which is broken every day though of course it now carries less traffic.  Gadfly, Hornet, and Wasp are keys each for a different Air Corps.  By the end of the month Hut 6 has broken a further two Air Corps keys, Cockroach and Locust; as well as those of two other Luftwaffe formations (Luftgau) Foxglove and Primrose. This month Hut 6 also breaks another German army key, that used for supply messages on the Eastern front. Kite had first been identified by BP in July 1941, so it is excellent to have it broken at last, particularly as the main Eastern front German army keys like Vulture are becoming harder to break as fewer messages go by radio in Russia as the land lines are repaired. Kite was broken by BP until virtually the end of the war.

Tunny and the Fish Codes. 

The other great feat to be completed at BP that month is the unravelling of the architecture of the Lorenz SZ40, a high-speed teleprinter type machine, the architecture of which is quite unknown to BP before the young chemistry graduate William Tutte, just down from Cambridge, gets to work in September 1941 after his boss, the brilliant John Tiltman, has decrypted one Fish message using ‘depths’, after a lucky break due to a careless German operator.  Bill Tutte and his small band of helpers work out that the machine has 12 code-wheels on which there are ranging from 23 up to 61 switchable teeth. (Each of the five digits of the character code stream passed through one of a series of five of these code-wheels where the digit might be changed from a 0 to a 1, or vice versa, depending upon the setting of the appropriate tooth on the code-wheel. The modified character stream then passed through a further series of five code-wheels, the remaining two code-wheels determining the rotation of the code-wheels). The unravelling of the architecture of what BP calls the Tunny machine by Bill Tutte and the Research Section, working upstairs in the Mansion, is undoubtedly one of the greatest intellectual achievements of BP, and it immediately enables the commissioning from Dollis Hill, the PO Research Establishment, of an emulator for Tunny. But will it enable BP to break the Fish messages that they now know carry the very top level Intelligence of the German armies? The Research Section under Captain Gerry W. Morgan, reporting to Col. John Tiltman, head of the Military Section and recently named as Chief Cryptographer of BP, now studies how the settings of the Tunny wheels might be worked out and how the Fish messages might be read. By July 1942 their good progress means that a team under Major Ralph. P. Tester can be set up to tackle Tunny regularly.

Communications with the Middle East.

If the codebreakers in BP are now into their stride and the communications within the UK are working well, all is not well with the communications between BP and the Combined Bureau in Cairo. By now the Y stations in the Middle East are intercepting many messages which all have to be re-encoded to disguise them for transit by radio back to BP, typically using the Typex machine which the Germans never broke, and that encoding stripped out when they reach BP.  But skilled operators are in very short supply – as the “wicked uncles” had pointed out to Churchill in the ‘Turing letter’ of last October.  It is still taking between two and five days for a message to reach BP from the Middle East, but there is often up to a month’s further delay before the Cypher Office can strip out our own encoding.  A million groups of accumulated undecyphered backlog from the Middle East in the Cypher Office have to be destroyed this month. At this time the Cypher Office is dealing with about ¼ million groups a week; by the end of 1942 staffing had been increased and the number of groups being handled had grown four-fold, and this was to double again by June 1943. 

The Leaks from the American Embassy in Cairo. 

It was not only Germany and Japan who found it hard to accept that the enemy might be reading their codes. In January 1942 the intelligence available to Rommel in the Western Desert is suddenly much improved, because the Italian Secret Service had been able to steal a copy of the US Black Code in which the US military attaché in Cairo, Colonel Fellers, communicated with the Pentagon. The British had rapidly started to keep their new ally well informed and so Rommel himself became almost as well informed about British plans as was London or Washington, and almost as quickly. This was of great service to Rommel in his counter-attack of 21st January.  This took the British by surprise, partly because BP has been unable to read Chaffinch since 6th December, and the Italian high-grade book cyphers are becoming difficult to read, though BP has broken two new Luftwaffe Mediterranean cyphers (Locust and Gadfly). BP has sent one clear warning of Rommel’s improved supply position on 19th January, but it is only one straw in the wind in Cairo where the local Intelligence team, unlike BP, believe that Rommel has suffered far more severely in the recent fighting than in fact he has.  The CIGS, Sir Alan Broke, wrote to the C-in-C in Cairo, General Auchinleck, after the loss of Benghazi on 29th January “I cannot help thinking that optimistic intelligence played a part in accounting for your troubles”.  In February Auchinleck replaced his Chief of Military Intelligence by Colonel de Guingard. When de Guingand complained that he had had no experience of intelligence work, the ‘Auk’ replied “Excellent, that is why I have appointed you”.  The information from the US military attaché was also to prove of much value to Rommel in his remarkable advance in May and June 1942 to Alamein, taking Tobruk on the way.  That source of information suddenly dried up on 24th July, because at last the US had accepted the warnings originating from BP, based on Enigma decrypts, that the Germans were reading their Black code.  At first the US had believed the warnings were a covert way of saying that BP was reading their code, just as had happened when the British had first warned Stalin that his codes were being read in June 1941. (Of course this may have been true in both cases but it did not alter the fact that the Germans were certainly doing so).  In fact Churchill had written to Roosevelt on 25th February 1942 saying “Some time ago… our experts claimed to have discovered the system and constructed some tables used by your Diplomatic Corps”. Finally in June 1942 the British bluntly informed Washington that their Cairo code was compromised, after reading a particularly unwelcome Enigma intercept of 29th May passing on intercepted information from Colonel Fellers that severely criticized the British military performance in Egypt.   Rommel’s Y station, that had been carrying out the reading of the Cairo Embassy messages and much more, was over-run in front of the Alamein line on 10th July by the Australians.  The Germans failed to break the replacement US military attaché codes, and by then BP had mastered the Africa Corps Enigma signals, which it was reading regularly.  But perhaps even more important the military commanders in N. Africa were at last coming to trust the Intelligence they were receiving from BP, to appoint better quality Intelligence staff, and to integrate them into the whole decision making process.

The Loss of a Purple Machine. 

 In one of the most embarrassing and regrettable incidents in the cryptographers’ war the British ‘lost’ a Purple machine in the confusion of the evacuation of Singapore.  It had been sent out to the Far East on a warship with express instructions that it should be conveyed only in a military transport, but for some unrecorded reason it was transferred to the freighter Sussex at Durban. The Master said that he had landed the case at Singapore at the end of December 1941 and claimed that he had a receipt for it. No trace of the crate was ever found. The Official Enquiry concluded “By this time the situation in Singapore was chaotic and it could have been destroyed or dumped in the sea by a demolition party”. Had the Japanese found the machine and recognised it for what it was, they would have tightened up on all their codes. It would appear that they did not find it. But telling their US colleagues about the potential disaster must have been agony for the BP management, especially just at this juncture when BP was trying to persuade the US navy that they now had a cryptographic partner with whom it would be advantageous to co-operate.  In view of the attitude of some senior US Navy personnel who did not seem to believe in co-operation with the US Army, at least in cryptographic affairs, it is hardly surprising that the US Navy found good arguments to resist co-operating with the careless Brits – even if BP was soon to have ample grounds for its complaints about the Press report in the Chicago Tribune that the ‘US Navy knew in advance all about the Jap Fleet’ before the triumph of the Battle of Midway. This report turned out to have stemmed from the US Navy. This time the Japanese did order emergency code procedures and then changed their code-books much earlier than the normal routine interval. But it is now known that the Japanese Court of Enquiry concluded that the US might have captured some codebooks rather than that they were reading their codes, making no mention of the reports in the US press.

 Like the others, the Japanese were very slow to accept that their enemies might be reading their codes.  But in the early months of 1942, the British code-breaking effort in the Far East is in disarray, with the main naval part of the Far East Combined Bureau moving in haste from Singapore in early January 1942 on a troop ship to Colombo, to be based at a school, Pembroke College outside the city that was now known as HMS Anderson. Before they left they had made some progress with the new codebooks for the Japanese General Operational key, called JN-25b by the US, but now progress is slow and they have lost a vital part of their Hollerith punched card equipment. It is the Pearl Harbour US navy team, called Hypo under the remarkable Joe Rochefort, who make the most progress. The British at Colombo are exchanging results, with them, with or without the permission of their seniors. The move to Colombo, and an outbreak of dengue fever when they get there, has broken the British continuity and it will be many months and further moves, before they can fully catch up. The army team from the FECB gets dispersed to Burma, India and Java.  Meanwhile BP is struggling to build up their Japanese code-breaking teams, with an extreme shortage of Japanese language experts who are now in huge demand.

The Bletchley Park Trust welcomes the preparation of these notes, but the authors are responsible for the statements and the views expressed.