THESE DAYS AMERICA may lead the way in its expenditure on military intelligence, but it wasn't always so. The NSA website pays tribute to code-breaker Herbert 0 Yardley in its 'Hall of Honor', but for much of his life Yardley was a pariah, cast aside at the end of the 1920s by an administration that sought to distance itself from his squalid trade. In The Reader of Gentlemen's Mail, David Kahn seeks to resurrect Yardley, and hails him as the most colourful and controversial figure in the history of American intelligence.

Yardley was born in Worthington, Indiana, in 1889. After leaving school, he worked for the railroad before ( successfully applying to become a government telegrapher in Washington. It was there that he started to investigate the security of codes, wondering why no agency existed purely to decipher foreign messages. He