Seventy Years Ago This Month at Bletchley Park

June 1941

A Notably Successful Month for BP. 

The invasion of Russia gives Britain a powerful new ally, though at first it looks like another disaster.  At last BP breaks a German army Enigma key, Vulture in use on the new Russian front; and the Luftwaffe field Sigint service key, Mustard, in use there is also broken in June. And then for 12 days until September BP is mastering the German naval key, Dolphin; reads their reserve key, RHV; and breaks the Italian navy C-38m machine.

Barbarossa: Hitler Invades Russia. 

To the surprise of Stalin and a few of his henchmen, but not of the other leaders in Russia or, for that matter, in Britain, Hitler invades Russia on the early morning of 22nd June. The size of the forces deployed by the Germans is without precedent, involving some 3,500,000 men, 3,350 tanks, 7,200 guns, supported by more than 2,000 aircraft. Their 152 divisions are supplemented by 14 Rumanian small divisions in the South and 14 Finish divisions in the North.  At first Hitler’s Panzer armies enjoy the overwhelming success that they have come to expect.  The Soviet air force loses 1,200 aircraft on the first morning, many lined up on their exposed airfields. By the end of the month some of the German spearheads have advanced 200 miles and the Germans begin to believe the end is in sight; General Halder, head of the German High Command notes in his diary “the objective to shatter the bulk of the Russian Army has been accomplished…It is thus no overstatement to say the Russian Campaign has been won in the space of two weeks”. But the fanatical defence of the poorly equipped and ineptly led Russian soldiers is already suggesting that this is not going to be so easy as Hitler’s other campaigns.  Many, though certainly not all, of the senior Russian commanders are incompetent, for most of the experienced officers have been purged. And the junior commanders are poorly trained and lack experience. They need tanks, communications, anti-tank weapons, and anti-aircraft guns.  But already the Russians deep devotion to their motherland is becoming apparent.  The Russians mount many uncoordinated counterattacks that tend to be suicidal lunges directed at the tip of the assaulting Panzers. In the first week of the assault virtually all the Soviet mechanised corps lose 90% of their strength. But the first encounters with the few Russian T34 tanks come as a nasty shock to the Germans who at last meet a match for their own armour. The advances in the Southern part of the long front have much less initial success than in the North or Centre of the line, for it is in there that the Russians had expected the blow to fall. But the German advance continues, encircling huge Russian hordes, though it proves difficult to prevent the Russians slipping out of the pockets, without their equipment but living to fight another day.  The vast spaces of Russia now loom before the German conquerors as they had before Napoleon’s all-conquering army over a century before. 

Barbarossa: Prior British Intelligence. 

Britain had obtained many signs that Germany was planning to attack Russia. As long ago as November 1940 Winston Churchill had come to believe that Hitler was planning to take this huge gamble.  But despite the numerous indications, both from diplomatic channels and, even better, from decrypts by BP, the British Intelligence Services are reluctant to believe our good fortune.  Hitler has continued to provide signs that he is going to invade the UK as a smoke screen for his real intentions, and it suits British Intelligence to believe this.  Then in May as the signs of the build up become overwhelming they form the view, shared by many neutral countries, that Hitler is simply piling on the pressure to persuade the Russians to agree to give them what they need without fighting.  But since at least the beginning of May, at BP those in the know have become convinced that this is no bluff.  They obtain their information primarily from the Luftwaffe Red key and the Railways Enigma Rocket.  And some of the best intelligence comes from reading the Magic messages that the Japanese Ambassador to Berlin sends back to Tokyo, sometimes directly after he has talked with Hitler.  For some weeks BP has been warning that the assault will be launched when the German preparations are complete in the second half of June.  In the last ten days the evidence from Red decrypts leaves no room for doubt that the attack is imminent. (In general the German forces are maintaining good radio silence as they always do before an assault, but in communicating with their forces in Northern Norway they have no choice but to use radio as there are no landlines).  The British Intelligence Services are warning that Russia will be unable to hold out for more than three or four weeks, and that then the Germans will rapidly turn round and mount the long awaited invasion of Britain.  Only Winston Churchill, who knows his history rather better than his advisors, expresses confidence that the Russians will hold out.

 
Barbarossa: Intelligence relations with Russia. 

Churchill had sent a warning to Stalin as long ago as the 3rd April. Other warnings followed from the British Ambassador to Moscow, Sir Stafford Cripps.  Stalin himself treated these warnings as a bluff, either by Hitler or Churchill, though it cannot have helped that Churchill was very circumspect about the source of his information. But perhaps as a result of these warnings, and some 80 others stemming from the USA, Sweden, etc, Russia has begun to step up its defence, though Stalin has been keen to prevent anything that Russia might do being treated by Germany as a provocation.  Over the years between the wars GC&CS took the reading of signals emanating from Soviet Russia as a priority target. Much to their regret, in 1927 the Government had chosen to publish the text of a decrypted intercepted telegram, which resulted in the Russians tightening up their diplomatic cyphers that remained unbroken until the Venona affair in 1943. But BP was reading certain relatively minor Russian military traffic right up to the German invasion. (Working at BP were several White Russians, including the veteran cryptologist, Ernst Fetterlein, who was said to have been the Czar’s chief cryptologist before the revolution).  On the very day of the invasion of Russia, Churchill, the life-long anti-Bolshevist, publicly pledged every support to Russia, and privately instructed BP to cease reading signals emanating from our new ally. (BP seems to have been remarkably slow to implement this; in June 1943 BP re-started work on Russian non-military codes, in a project named “ISCOT”). But from reading German signals BP rapidly becomes aware that the Germans themselves are reading some Russian signals. Much of the intelligence on the Russian front obtained by BP stems from that usual gift-horse, the Luftwaffe Red key. Then within a few days of the offensive, with the number of German army Enigma messages rising abruptly, Hut 6 breaks a key, called Vulture at BP, used by the German armies to communicate with their Army HQ.  It had been first identified by BP in April 1941 and was broken a few times between June and September 1941 and then from October until December with some regularity. Then it was lost for over a year due to the introduction of landlines. But while it could be read it provided regular and detailed operational reports, as well as occasional high-level appreciations, statements of intent and some supply information; high quality information on the Russian front that was available to Britain from no other source until BP broke the relevant top-level Fish cyphers in 1943. 

It is tragic that Intelligence cooperation with Russia did not develop satisfactorily.  Churchill orders that the British Military Mission in Moscow should warn the Russians that certain of their codes are being read by the Germans, but this at first provokes the reaction that it is the British who are reading the Russian codes, though the Russians did finally change some of their codes. (Strangely, this was also the first reaction of the Americans when the British warned them that the Germans were reading the code of their military attaché in Cairo in 1942).  Within a couple of days of the invasion starting Churchill was instructing the reluctant “C” (Sir Stewart Menzies, head of the Secret Service) to send certain information derived from the Enigma decrypts to Moscow, but disguising the source.  A war of wills develops between the two, but a stream of messages does go to Moscow, the information being disguised as coming from “very reliable sources in Berlin”.

Naval Section at BP: the Aftermath of the Sinking of the Bismarck. 

When the Bismarck had been intercepted having turned south to run to Brest and finally been sunk on the 27th May, her accompanying cruiser, Prinz Eugen, had escaped in the fog and was able to reach Brest undetected on 1st June.  By now most days Hut 8 was breaking cryptographically the main German Enigma naval key, Dolphin, but during May with delays of three to five days, which was too slow for operational purposes.  On 28th May they managed to read much of the traffic in Dolphin related to the mission of the Bismarck, and this provided information about the position of 8 German supply ships strung out across the Atlantic awaiting the Bismarck.  During June the delay in breaking Dolphin sharply reduced, as Hut 8 was able to use the key sheets for June captured from the weather ship München on 7th May and the U-110 on the 9th May.  They were learning to use better cribs, often derived from the “kisses” provided by repeats of information in the dock-yard hand cypher, Werft, which Naval Section at BP was reading, and from the short weather reports from the U-boats repeated on the powerful transmitter, DAN, being read by the meteorologists in Hut 10.  By 21st June all but one of the 8 supply ships were disposed of, 6 of these as a direct result of using the Enigma information.  Between 21st June and 11th July a further 7 supply or weather ships were sunk, though their interception owed nothing to Enigma information because the Admiralty had decided not to make use of this information in cases where that might betray the crucial secret. But they made an exception for the weather ship Lauenburg, which was boarded on 28th June, a date chosen to yield key sheets for both June and July.  Captured documents continued to be of great assistance from time to time for the breaking of naval Enigma and other cyphers; procedures were laid down to ensure no opportunity was missed.  But the Lauenburg was the last time a “pinch” of this type was executed, for fear of giving away the secret.  And indeed the German Naval Service did institute an enquiry following the loss of the supply ships but decided, as on other occasions, it could not have happened as a result of their Enigma cyphers being broken. By the end of June the staff in Hut 8 had been built up, and BP has 5 Turing Bombes, and will soon have 6 so that at least one can always be dedicated to naval work.  Alan Turing leads the intellectual attack on naval Enigma, but by now his team has been strengthened by Hugh Alexander from Hut 6, and steadily Hugh takes over the organisation and administration of the now fast growing team in Hut 8, for Alan is not well fitted to that type of work; soon Hugh emerges as acting head and becomes formal head of Hut 8 when Alan leaves, temporally, to visit the USA in November 1942. (When someone asked who is head of the Hut it is said that Hugh replied “Well, I suppose I am”).

Naval Section: Other Successes:

During June 1941 Naval Section under Frank Birch at BP makes two other break-throughs.  The Swedish Haglin machine C-38m had first been used by the Italian navy in December 1940, when it began to replace their un-steckered Enigma machines because the Germans had objected to their poor security – quite rightly as Dilly Knox and his team in the Cottage were reading the relatively few Enigma messages they sent. The C-38m is first broken in June, probably by Hut 8; and thereafter each month the key settings were rapidly found by a three-man team in Hut 8, including Colin Thompson, but it was the cryptographers in Hut 4 who then did the hard work finding the individual message settings by the “rodding” technique. They were part of the team that was usually working on hand-cyphers. 

Prof E.R. Vincent leads the Italian section working on the Haglin machine, and inevitably his girls become known at BP as the “Hags”.  The C-38m breaks prove extremely useful in the Mediterranean to pin-point the convoys taking supplies to Rommel’s army in North Africa, and it was broken regularly until the Italians surrendered in August 1943.  In June 1941 only 4% of the Axis supply traffic to North Africa is sunk, but by November 1941 this had risen to 62%, thanks to the C-38m breaks and to those of the two Luftwaffe keys, Red and Light Blue, when there is air-cover provided for the convoys.
And also during June, due to the capture of material probably from the München or U-110, Hut 4 is able to read the Reservehandverfahren, known at BP as RHV. This is the reserve cypher carried by all German ships in case Enigma is unusable – and on some ships as an alternative to Enigma. Hut 4 soon learns to read it cryptographically, and continues to do so for the next 40 or so months.  It provides some 1,400 signals at an average of 12 per day and is valuable both for the information it generates in its own right, and as a source of excellent cribs for naval Enigma.  A team of cryptographers in Hut 4, led at one time by Dr C.T.Carr, carries out the work on these hand cyphers. The team included J.H.Plumb (later Sir John Plumb the historian at Cambridge), A.S.C.Ross (later to be associated with “U” and “non-U” speech), Bentley Bridgewater (later Secretary of the British Museum), James Hogarth (who arrived as a private, was not allowed to take time off to become an Officer and so left BP at the end of the war as a very improbable RSM), and Christopher Morris (famous in Hut 4 for using on the telephone a “code” based on cricket). This team read at one time or another some 20 or more of the 27 hand cyphers used by the German navy.  But they often felt themselves overshadowed by the Enigma wizards in Hut 8, and for a brief period the name “Operation Cinderella” appeared over their office door at BP.

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