Arrow, London, 1980, 1st pr thus.  ISBN 0-09-922770-3.  Trade soft cover, 398 pages including Notes, Appendix, Bibliography, and Index.  Wraps have a bit of edge and cover wear, reading creases on spine and along front spine edge; outer page block darkened with numbers stamped on top edge.  Interior clean and unmarked with lightly browned but not brittle pages and occasional age spot; binding sound; black & white photo plate section.  ‘It was the most vital secret of the Second World War.  We can talk about Ultra now.  But until recently it was kept virtually secret.  Since then, our view of the war could never be the same.  Now, using information newly made available in the Public Record Office, as well as extensive interviews with the scientists and agents involved, Ronald Lewin recounts the fascinating story of the most successful Intelligence operation of all time.’ (from rear wrap)