Many people have never heard of Mavis Batey, but her reputation in the intelligence community - at least, those who study its history - is significant. She died a few days ago, but her memory will live on for generations of codebreakers, who will continue to study her achievements.
The Telegraph reports in its obituary:
Mavis Batey, who has died aged 92, was one of the leading female codebreakers at Bletchley Park, cracking the Enigma ciphers that led to the Royal Navy’s victory at Matapan in 1941.
She was the last of the great Bletchley “break-in” experts, those codebreakers who found their way into new codes and ciphers that had never been broken before.
. . .
Arguably her most important role ... was in the collaboration with [Dilly] Knox and Margaret Rock on the breaking of the Enigma cipher used by the German secret service, the Abwehr.
MI5 and MI6 had captured most of the German spies sent to Britain, and those in the neutral capitals of Lisbon and Madrid, and turned them back against the Germans, feeding them false information designed to deceive them in an operation known as the Double Cross system.
But they had no idea whether or not the Germans believed this intelligence, as the Abwehr Enigma was so complex that Hut 6 had been unable to break it. It had four rotors instead of the standard three, and unlike other machines they rotated randomly with no predictable pattern.
Knox took over the task of breaking it, using Mavis Batey and Margaret Rock as his assistants, to test out every possibility. On December 8 1941 Mavis Batey broke a message on the link between Belgrade and Berlin, allowing the reconstruction of one of the rotors.
Within days Knox and his team had broken into the Abwehr Enigma, and shortly afterwards Mavis broke a second Abwehr machine, the GGG, adding to the British ability to read the high-level Abwehr messages and confirm that the Germans did believe the phoney Double-Cross intelligence they were being fed by the double agents.
This allowed the XX Committee, which was running the double agents, to send a stream of small pieces of false intelligence that would build up a complete picture of a fictitious First US Army Group, which was forming up in East Anglia and Kent to lead the main Allied invasion force.
The false intelligence led the Germans to believe that the main force would land on the Pas de Calais rather than in Normandy. As a result Hitler insisted that two key armoured divisions were held back in the Calais area.
Brigadier Bill Williams, Montgomery’s chief intelligence officer, said that without the break into the Abwehr Enigma the deception operation could not have been mounted. The forces in Calais would have moved to Normandy and could well have thrown the Allies back into the sea.
There's much more at the link. Recommended reading.
Here's a presentation from the Royal United Services Institute. It was to have been delivered by Mavis Batey in 2011, but she was prevented from doing so by ill health. She sent her memoir of her code-breaking career to the RUSI, where it was read by Kate Adie. It's well worth watching.
We'll never know how many tens of thousands of Allied servicemen were saved from becoming casualties (killed, wounded, captured or missing in action) through the work of Mrs. Batey and her colleagues; but it must have been a very substantial total.
May she rest in peace.