Sixty two top secret decrypts of wireless traffic of the SS Ordnungspolizei, or non-party unformed police, which revealed the "unspeakable activities" of Hitler's Einsatzgruppn or "action squads" in occupied Russia, were released yesterday at the Public Record Office Kew.
The documents call into question how much Churchill's government knew about the Nazi atrocities. But Dr John Fox, lecturer in Holocaust studies at Jews' College in London, whose discovery of parallel files in the American archives forced the British disclosure, said yesterday: "These decrypts could only have been seen by a select few in the Cabinet. A lower-ranking Foreign Office official Roger Allen wrote on 25 January 1942, 'I suppose no one will ever be able to establish the facts about the German occupation of Russia.'
"This proves that the Foreign Office was not privy to the facts and in fact the decrypts were kept in a drawer until much later and were used as background evidence in preparing charges against alleged war criminals in the 1980s."
In addition, the release intriguingly highlights the revelation by Sir Harry Hinsley in his official history of wartime intelligence that the Ordnungspolizei suddenly adopted a more difficult hand cipher in September 1941, temporarily baffling Bletchley Park.
On 13 September 1941, the day after Bletchley decrypted the news that the Nazi murder squads had bragged about "one of their greatest successes in liquidating 1,548 Jews", SS general Kurt Daluege - in charge of ethnic cleansing in the aftermath of Operation Barbarossa - signalled his commanding officers: "The danger of decipherment by the enemy of wireless messages is great. For this reason only such matters are to be transmitted by wireless which can be considered open, but no information which contains states secrets or calls for a specially secret treatment. In this category fall exact figures of executions." The euphemism for mass executions was to be "action according to the usages of war".
Within days Bletchley announced "although an entirely new form of cipher was inaugurated for the Russian messages continuity in the breaking of the previous keys made it possible to break into the new ones too and whereas up till 12 September only three had been broken, since then only one has remained unbroken".
The codebreaker wrote: "In Krementschug on 30 October 1941 'the action' was on a scale exceeding even the previous brutality of the German police." The local commander, Jeckeln, gave permission for the massacre of local Jews "and we may suppose that the butchery went on all night".
Planning for the systematic murder of Jews, which Himmler regarded as a test run for the Holocaust, began as soon as the attack was launched on Russia.
The SS high command was even prepared to accept inflated figures for victims as long they thought they were Jews. On 4 August, two months after Barbarossa, an SS report stated "the operations of the SS Reiter [Cavalry Brigade] continues with a further 3,600 executed so that the number carried out by them amounts to 7,819; a total exceeding the 30,000 mark."
The codebreaker commented: "The tone of the message suggests that ... a definite decrease in the total population of Russia would be welcomed in high quarters and that the leaders of the three Sectors [of the Einsatzgruppn] stand somewhat in competition with each other on their 'scores'."
Among the papers' other revelations is the fact that a train load of 1,296 Hungarian Jews was dispatched to Auschwitz in August 1943 for experiments into malaria, under the control of Himmler's Special Commissar for combating animal pests
There were also details of the plunder of Russian art treasures by squads controlled by the Foreign Minister Joachim Ribbentrop. The greatest prizes were reserved "for the use of the higher Nazi bosses in their villas; the lesser bosses had to be content with rare books and costly vases."
The discovery last week of a painting from the Amber Room of the Tsar's summer palace outside St Petersburg, is highlighted by a report that the palaces there had been robbed of their artistic treasures.