Rozanne is the daughter of Charles Medhurst, a senior officer in the RAF who became air chief marshal after the war.

'Imagine the thrill!' she says, looking back.

There is only one story in this book of the kind of discovery usually associated with code-breaking, in which, late one night in 1943, the young Rozanne Medhurst's eyes were the first to see the news that Italian torpedo bombers and transport carriers were due to leave Tripoli and head across the Mediterranean into Sicily, in flight after the 'desert war' in North Africa. Their work, which helped win the war, was largely unsung and unheralded and not just because it was top secret. There are 15 women in this book, their life stories ranging across the English social spectrum women who worked behind the scenes, often with little idea of what it was exactly that they were doing. The youngest of her interviewees, 86-year-old Muriel Dindol, was 14 when she went to work at Bletchley Pamela Rose was 96, the oldest of the women Dunlop found to meet. But those women are all dead and Dunlop was determined to write a book full of living voices: an important task when we are, as far as the Second World War is concerned, approaching the limit of living memory. This isn't a book about the female cryptanalysts at Bletchley – and there were some, though the names of Hugh Alexander, Gordon Welchman, Harry Hinsley and Alan Turing have always eclipsed those of Joan Clarke (played by a skittery Keira Knightley in the dismal travesty that was The Imitation Game), Ruth Briggs, Margaret Rock and Mavis Lever.

But by 1944, there were three women for every man at Bletchley: women who were crucial to the success of the place but whose stories have barely been told. That astonishment was found, Tessa Dunlop recounts in her lively history, The Bletchley Girls, in a section of the review entitled Medium or Low-Grade Labour, which gives a good idea of the estimation in which most of the women who worked at Bletchley were held. 'It was astonishing what young women could be trained to do.' There is a note of surprise in the post-war review of the work that went on at Bletchley Park – for decades a site shrouded in secrecy but now known the world over as the place where the Nazis' 'unbreakable' Enigma code was cracked.

The Bletchley Girls by Tessa Dunlop