These sheets were typed up by a Mrs. Tenney, an aged vicar’s wife who works at Bletchley Park. Mrs. Tenney has a peculiar job which consists of the following: she takes two sheets of onionskin paper and puts a sheet of carbon paper between them and rolls them into a typewriter. She types a serial number at the top. Then she turns the crank on a device used in bingo parlors, consisting of a spherical cage containing twenty-five wooden balls, each with a letter printed on it (the letter J is not used). After spinning the cage the exact number of times specified in the procedure manual, she closes her eyes, reaches through a hatch in the cage, and removes a ball at random. She reads the letter off the ball and types it, then replaces the ball, closes the hatch, and repeats the process. From time to time, serious-looking men come into the room, exchange pleasantries with her, and take away the sheets that she has produced. These sheets end up in the possession of men like Waterhouse, and men in infinitely more desperate and dangerous circumstances, all over the world. They are called one-time pads.