Masked Dispatches: Cryptograms and Cryptology in American History, 1775-1900

Chapter 18. 1867 State Department Code

Because of the expensive 23 November 1866, diplomatic cable to John Bigelow in Paris, Secretary William Seward promptly discontinued use of the old Monroe Code and "set to work as early and prosecuted as vigorously as possible the construction of a new and frugal cipher code. . . ."^[265] As explained in the State Department introduction to this new code, the magnetic telegraph required the sender to translate code numbers into letters since numerical signs could not be transmitted. Thus, it happened that fifteen to twenty letters were necessary to express a single letter of the old Monroe Code. A determined and chastened Seward wanted a much more economical system for his secret dispatches.

The newly designed ...