Perry wrote that the British let Coventry be destroyed lest Ultra be revealed. Kahn doesn't believe that. From ``Kahn on Codes'', p. 110: Nor, to debunk another story, did Churchill let Coventry be destroyed because he believed that defensive measures would risk the secret of ULTRA. Critical analyses of documents show that this is pure myth. The footnote cites F.H. Hinsley with E.E. Thomas, C.F.G Ransom, and R.C. Knight, ``British Intelligence in the Second World War: Its Influence on Strategy and Operations'' (London, 1979- ), I:528-48; N.E. Evans, ``Air Intelligence and the Coventry Raid'', Royal United Services Institution Journal (September 1976), 66-73. I don't have access to either of those publications, so I can't assess that further.