Jim Choate wrote:

Myer implimented including a 'cipher disk' whereby the Union was able to change their telegraph codes on an hourly schedule. It was apparently very effictive in dealing with taps and such.

Anyone know of another source that discusses this disk?

Myer's code and cipher disk (with illustration) are briefly described in Fred Wrixon's "Codes and Ciphers" along with an entry on Civil War crypto with a photo of a Confederate cipher disk. We've put the entries and illustrations at: http://jya.com/cydisk.htm The book is: "Codes and Ciphers: An A to Z of Covert Communication, from the Clay Tablet to the Microdot," Fred B. Wrixon, Prentice Hall, 1992, paper. $18.00 ISBN 0-13-277047-4