In May 1779,
Continental Army Major General
Benedict Arnold initiated what became a series of communications with
British Army Major
John André, the adjutant and spy chief to Lieutenant General Sir
Henry Clinton, the commander-in-chief of British forces in
North America. In these communications, which were at first mediated by Joseph Stansbury, a Philadelphia merchant, Arnold offered his services to the British. André responded to this offer with a letter dated May 10, 1779, in which he described the types of services Arnold might provide, and described a code which they should use to obscure their communications. The book used as a key to the cipher was either
Commentaries on the Laws of England by
William Blackstone or ''
Nathan Bailey's Dictionary''. The cipher consisted of a series of three numbers separated by periods. These numbers represented a page number of the agreed book, a line number on that page, and a word number in that line. Arnold added missing letters or suffixes where he could not find a match in one of the books. For example, 120.9.7 would refer to the 120th page, the 9th line on that page, and the seventh word in that line, which, in the following example is decoded as "general". The actual communications were often disguised by embedding it in a letter written by Arnold's wife
Peggy, where the cipher would be written in
invisible ink, but might also have been disguised as what appeared to be routine business communications. ==Coded example==