As we tour the machines, gazing with awe at the banks of circuits and switches, the man next to me, Patrick Beautement, says that his mother was one of the thousands of women who worked in these huts. He said ‘In a letter she sent me before she died she mentioned her work. I don’t remember all that much about it, she said, it was terribly boring. The way they kept everyone separate, so even just mentioning a name got you terrible black looks from your colleagues, made it all so difficult to recall.’