The people who worked for Unit 701 placed national security above all other considerations, and the strict secrecy that their profession demanded resulted in them losing even the most basic of personal freedoms: they did not even have the right to send mail. It was only after being thoroughly investigated that a decision would be made as to whether the letter should be delivered to the intended recipient. If you wrote a letter to them, whether or not the person you posted it to would be able to read it would depend entirely on what you had written; if it aroused the slightest suspicion, there was no chance of them being able to look at it. Even if they were lucky enough to be able to get the letter, they would only be allowed to read it once, after that it would be returned to the archives, for the individual concerned had no right to keep it. If you go back twenty years, supposing that you were so fortunate as to receive a letter from one of them (and that possibility was very remote unless you were a close relative) you might have wondered why the letter was always a carbon copy. The fact is that there was nothing to be surprised at in this, because the original of any letter that they sent would have to go to the Party. In the days before photocopying machines, the best way to make multiple copies was to use carbon paper. An even more unimaginable intrusion into their lives was that when they left the unit, they would have to hand over all written material, including such things as private diaries, to be kept by the archives department, until the day when their contents were no longer deemed to compromise national security, at which point they could go back to their original owner.

That day was their Declassification Day.

That day, old secrets finally came out into the open.

Originally there had been no such thing: it started in 1994, three years after I first bumped into the two men from my old home town. That was the year that Director Qian finally retired, and I first got the idea of writing this book. As I am sure you understand, I wrote this book not because I got to know the two men from the plane, but because they held the first ever Declassification Day in the history of Unit 701. Because of that Declassification Day, I had the right to go to the mountain and walk round the valleys, seeing what there was to see. Thanks to Declassification Day people from Unit 701, or rather it would be more correct to say people who were no longer deemed to hold secrets vital to the nation’s interests, were allowed to be interviewed by me.

You do not need to be told that without Declassification Day, this book could never have been written.

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