United States Diplomatic Codes and Ciphers, 1775-1938 is the first basic reference work on American diplomatic cryptography. Weber's research in national and private archives in the Americas and Europe has uncovered more than one hundred codes and ciphers. Beginning with the American Revolution, these secret systems masked confidential diplomatic correspondence and reports. During the period between 1775 and 1938, both codes and ciphers were employed. Ciphers were frequently used for American diplomatic and military correspondence during the American Revolution. At that time, a system was popular among American statesmen whereby a common book, such as a specific dictionary, was used by two correspondents who encoded each word in a message with three numbers. In this system, the first number indicated the page of the book, the second the line in the book, and the third the position of the plain text word on that line counting from the left. Codes provided the most common secret language basis for the entire nineteenth century. Ralph Weber describes in eight chapters the development of American cryptographic practice. The codes and ciphers published in the text and appendix will enable historians and others to read secret State Department dispatches before 1876, and explain code designs after that year.

This is an examination of codes and ciphers as they figured in American History prior to the twentieth century, prior to the era of wireless or radio communication and the advent of the electronic age. It forms a backdrop for understanding modern cryptology and the role of cryptology in the growth of this nation. Cryptology, the art and science of code-making and code breaking, depends on the prevailing state of technology and the perception of threat.

The art and science of code-making and code-breaking is driven both by the risk inherent in an adversary's ability to read an intercepted communication and the technology available to mitigate that threat efficiently and cost-effectively. This is true both for today's computer-driven cryptography and cryptanalysis and the simpler, yet no less vital codes and ciphers used in the past.In "Masked Dispatches: Cryptograms and Cryptology in American History, 1775-1900," the beginnings of American cryptography are portrayed as rooted in the nation's origin in revolutionary conspiracy. Although the technology consisted of the use of messenger and hand-written correspondence or signals ("One if by land, two if by sea"), the risks of detection and betrayal of secrets was just as great as in the present day."Masked Dispatches" presents some of the Founding Fathers as active participants in spycraft. America's first espionage code was devised by Benjamin Tallmadge, General George Washington's director of secret service, for use by a spy ring set up in New York in 1778. Another chapter discusses Washington's supplying of invisible ink to Tallmadge. Not surprisingly, Thomas Jefferson's contribution to the world of codes and ciphers was a mechanical device - a wheel cylinder. Once America won its independence, it continued to rely on the devices and methods used in the Revolutionary period. During the Civil War, both sides employed ciphers which, although not much in advance of those used in the 18th century, generally succeeded in keeping their secrets. Spies in the field, such as the Union's Elizabeth Van Lew in Richmond, used simple yet effective substitution systems, while even Abraham Lincoln dabbled in primitive types of encryption.Whether recounting the cryptographic efforts of prominent Americans or the more mundane role of successive diplomatic codes in keeping State Department transactions confidential, "Masked Dispatches" provides both fascinating narrative details and extensive examples of encrypted dispatches and cipher systems. This unique view of America's early history will prove invaluable to diplomatic and military historians as well as anyone intrigued by spycraft, codes, and ciphers.