Hi, i once read Gitta Sereny's Speer biography. It has an impressive description of Speer's visit to the Mittelwerke. I don't know, if there is an englich translation. Sereny, Gitta: Das Ringen mit der Wahrheit, Albert Speer und das deutsche Trauma. Munich 1995, ISBN 3-7632-4524-3 Best, Christian.