Overview of Civil War Codes and Ciphers

The Signal Corps - Antietam National Battlefield (U.S. National Park Service)

Civil War Puzzle Station Activity - Abraham Lincoln

Codes and Ciphers – Mathigon

Confederate Ciphers (Other Than Vigenere) during the Civil War

Codes, Ciphers, and Secret Languages by Fred B. Wrixon

Cryptology - Ancient, Codes, Ciphers

Caesar cipher - Wikipedia

Union Army Cipher Wheels - Civil War Encryption Device

Decoding a Civil War Cipher - Country Roads Magazine

Confederate Cipher Disc

Codes, Ciphers and Secret Writing (Paperback)

War D[epartment] Ciphers Sent Jany 27th 1864 to Dec 2[nd?] - Thomas T. Eckert Papers - Huntington Digital Library