This is a replica of a Confederate Cipher Disk, the principal
coding/decoding system used by the American Confederate government
and military. It was based on a centuries old system known as the
"Vigenere System" but called the Vicksburg System by the Confederate
States of America.
The cipher disc depicted in the photo is a faithful replica of
the original. Only five are known to have survived. One of the
original cipher discs was given to the Museum of the Confederacy in
Richmond VA. by Major Graham Davis who, as assistant adjutant to
General S.G. French, used it to encipher
and decipher messages for his commander. Cipher discs were
probably made at the request of E.P. Alexander who, in 1861 was
ordered to establish a Confederate Signal Corps.