Seventy Years Ago This Month at Bletchley Park

January 1941

A Brighter Dawn? 

The New Year comes in with continuing good news from the North African Western Desert where General Wavell’s offensive is going extremely well, capturing Bardia on the 5th, racing on to take Tobruk on 22nd and the two prongs of the brilliant pincer movement closing beyond Benghazi early in February after an advance of 500 miles, taking 130,000 Italian prisoners.  Then on 19th January the British offensive in East Africa opens, with forces under General Cunningham entering Italian occupied Ethiopia from the Sudan. Perhaps the growing euphoria, stemming from the belief that the Italians would soon be thrown out of North Africa, would have been questioned if only the public could have been told just how small and vulnerable our forces there really are.   The good news from Africa serves to divert attention and soften the pain of the Blitz, though the disaster when a bomb falls on London’s Bank tube station killing 111 people sheltering in the tunnels is hard to hush up.  And the arrival of the Luftwaffe in the Mediterranean is made all too clear with the sinking of the cruiser HMS Southampton and the severe damage caused to the aircraft carrier HMS Illustrious on 10th January. If the public had realised that the German Africa Corps would soon be arriving in North Africa maybe they would have wondered if the British victories might not herald a false dawn?

General O’Connor’s Brilliant Victory in the Western Desert. 

When General Archibald Wavell launched his desert campaign on 9th December he had only intended it to last for 5 days.  But the great success in which just two British divisions of 30,000 men overwhelmed seven Italian divisions of 250,000 inevitably led to demands from the pugnacious Churchill that the attack be continued: “Your first objective now must be to maul the Italian army and rip them off the African shore”. Whether Gen Wavell hesitates or not – and he certainly does not pause for long - his dashing field commander General Richard O’Connor is not the one to let such an opportunity pass. When the campaign starts again on 1st January he leads the 7th Armoured division round the flank of the Italians across the desert sands while the 6th Australian division pushes them back along the coastal road, making their first acquaintance with Tobruk on 22nd. When the jaws of the pincer movement closed at Beda Fomm on 7th February 20,000 Italians had been killed or wounded and 130,000 taken prisoner for the loss of some 500 British and Australian dead and 1,400 wounded.  The Italians had lost 850 guns and 400 tanks.  It was a truly remarkable feat of arms; perhaps the reason why the British public at large pays so little tribute to their great field commander, Richard O’Connor, is that he himself was to be in “the bag” in a few weeks time when General Rommel and his Africa Corps, learning much from O’Connor’s example, threw the small and depleted British army back to the Egyptian frontier.

It does not take away from this great British feat of arms to point out that it could hardly have been achieved without the excellent and copious Intelligence information that was available to General Wavell.  This came primarily from decrypts of the Italian air force and other Italian cyphers at BP and at the “Central Bureau Middle East” in Cairo, and from the Y force that provided excellent tactical information throughout the campaign.  The brave dash across the desert would have been foolhardy in the extreme had it not been known from the many intercepts that no significant enemy forces stood in its way.   Another result of this stream of excellent intercept information was that the impact of the deception campaign that Gen. Wavell mounted could be immediately monitored and adjusted accordingly, building on what the enemies own Intelligence services are reporting, and never straying too far from what the enemy already believes.  It is said that Archibald Wavell had learnt the benefit of deception from General Allenby when he had served on the staff of that great general in the campaigns in Palestine in 1917/18. So Wavell established under Col. Dudley Clarke a private deception team known as A Force, working, apparently, from a partially converted brothel in Cairo. (Hut 3, the Army & Air Force Intelligence team at BP who one might expect to have had a direct interest in the work, was told almost nothing about this very secret force for some years).   In the end A Force and their often-unwitting agents succeeded in persuading the enemy that the Allied Desert Army was twice as large as it really was, and kept up that deception throughout the North African campaign and beyond.  This success was the pattern for future deception programmes for the Mediterranean theatre, for the landings in Normandy, and for Gen Slim’s offensive in Burma, but to succeed they all required adequate access to the enemies’ thinking, based on signals interception and the decryption work of BP and the field Y service.

The East Africa Campaign. 

On 19th January General Cunningham attacks the Italian forces in Eritrea, Somaliland and Ethiopia from the Sudan.  The date is chosen because of a decrypt instructing the Italians to withdraw from Kassala, a town in the Egyptian Sudan occupied by them when they declared war in July 1940. The campaign, after a shaky start, develops into a three-pronged advance on Addis Ababa, and proves another triumph for very limited British forces, in which 420,000 Italian troops are killed or captured for the loss of only 3,000 British casualties.  At every step they are aided by reading Italian signals. From the first day of the five-month campaign the British were able to read, it is said, every single operational order issued by the Italians. It was a triumph for the British cryptographers, yet is little remembered today.

The Breaking of the German Railways Enigma. 

 Hardly glamorous but of very considerable strategic significance was the struggle at BP in the winter of 1940/41 to read the German Railways Enigma.  BP first identified it in June 1940, and it is known that it was the great cryptographer, Colonel John Tiltman, head of the BP Military Section, who first unravelled the nature of the German railways cypher system in that summer. (To those few in the know, John Tiltman was already seen as an outstanding cryptographer for he had taught himself enough Japanese to break the Japanese military attaché cypher machine in 1933). Because at the time the near-commercial version of the Enigma, without steckers (plug-board), was used carelessly “without security precautions” by the railways, John Tiltman was able to build up enough material on one key setting to be able to read some messages, which consisted largely of numbers forming timetables.  Then the Enigma experts in Hut 8 were called in, where Alan Turing asked Joan Murray (née Clarke) to try out a description he had written of a method for working out wheel wiring.  This was easily carried out and the wiring of the special code-wheels used on the railways’ machines was established.  It is said that all the messages were read until the traffic ceased on 27th August 1940, though it would appear that no-one at BP could make much sense of the resulting sets of figures.  (Alan Turing used the Railways machine to illustrate various crypt-analytical methods in a training manual “Treatise on the Enigma” that he was writing at the time, always known affectionately at BP as “Prof’s book”).  On 23rd January 1941 the Germans introduced a new variant used by the railways in the Balkans, and then extended it to Eastern Europe and then to Russia (often carried by radio, no doubt because telephone line communications were simply too unreliable in those regions, unlike in Western Europe until bombing led to the use of some radio communications there from September 1942).  The Balkans Railways key, called Rocket at BP (a later Railways version was called Stephenson though it seems to have been miss-spelt as Stevenson), was broken by Hut 6 on 7th February 1941 and read and understood regularly once the BP Intelligence staff had called on the help of experts in the “Railway Research Service” belonging to the UK railway companies. Because there was no stecker-board and the traffic was very stereotyped, it could be broken largely by cribs and hand-methods with occasional use of the precious bombe-time when stuck. This material gave details of train movements, such as contents of trainloads, routes, times, and entraining and detraining points.  It was absolutely invaluable in revealing the preparations and scale of the offensive operations the Germans were planning for the Balkans, and Russia. 

The Slowly Increasing Number of Bombes. 

The first operational Turing bombe, Agnus Dei or Agnes, had been delivered to Hut 1 at BP in August 1940, followed by the refurbished prototype bombe, Victory, to Wavendon in September.  In November 1940 Cmdr Edward Travis had written that two more bombes (which he still called “Spiders”) were due to arrive in the middle of December, but it would appear that they were delayed. It seems probable that the third “standard” bombe arrived in January 1941, but the fourth was probably delayed for modification to add an “automatic typewriter” to print and check stops. This was the first of the “Jumbo” machines and was in service by the end of March.  (It was so-called, or so the bombe-girls tell us, because of the trunk of cables that ran from the bombe to the automatic stop-tester and teleprinter). Cmdr Travis pleads for 40 to 50 bombes, on the basis of “two Spiders for each colour that we break regularly and more Spiders to deal with the more difficult colours…. The Naval problem requires more time and is perhaps more important because there are no landlines to take the most secret traffic. I believe we could break the Naval traffic day after day if we had about 35 Spiders available”. Allowing for periodic overhauls “it would be wiser to aim for between fifty and sixty”. This correspondence includes a request for bombproof accommodation that emerged, in March 1941, as Hut 11.

The Use of the Limited Bombe-Time. 

 With only the two or three bombes available, bombe-time is in huge demand.  It is needed regularly for breaking the very useful Luftwaffe general-purpose key, the Red, and the Brown key used for the navigation beam teams of the Pathfinder bombers, and for attacks on the very difficult Naval Enigma keys.  The bombes are also needed for experimental and initial break-in work on the Green, Orange I, and Violet keys.  The Green key was the German Army Home Administration key, which has been described as Hut 6’s toughest proposition.  It had been one of the first keys to be broken for one day in January 1940, and Hut 6 was still trying to break it again at this time at the start of 1941.  In fact it was only broken 13 times in the whole course of the war, and latterly then only with some help from Prisoners of War. It is the proof of how secure Enigma could be if properly used.  Orange I was the general-purpose key of the SS, the elite troops of the Nazi Party’s private army. It had been identified by BP in the early days of the war and was first broken on the 10th December 1940.  Thereafter it was read “with many ups and downs” until late in the war.  It carried general SS administrative material, including matters related to the organisation of the concentration camps. The Violet key had been first identified by BP in November 1940 as the general Luftgau key and was used for a short time until separate keys replaced it for each Luftgau (a Luftgau was an administrative sub-division of the German Air Force).  BP first broke the Violet on 24th December 1940, and then in January 1941 identified the Light Blue as being used by the Luftwaffe in North Africa, which of course obtained priority attention.  On 2nd January 1941 BP broke Gannet I for the first and only time.  It turned out to be the key of the German Amy Command in Norway, and so had little significance and probably was not treated as worth much bombe time, though it was broken again in a different form in August 1943. 

And so at this time BP is breaking the German Air Force keys but virtually none of the Army keys, no doubt primarily because there is relatively little army movement and so they could use landlines. But BP is obtaining considerable information on the German army from the Luftwaffe Red key and is about to break the renewed Railways key, which would give plenty of information on the German Army movements to the East and Greece.  Except for a few days after a capture in April 1940, at this time BP has failed to break any of the German Naval Enigma keys despite the fact that communications to ships at sea have to go by radio and so could be intercepted.  Much BP bombe time and effort by Hut 8 is trained on Dolphin, the important Home Waters key, which was to be finally broken regularly from August 1941.

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