Keeping Secrets, Part 1: Arbitraries

By Daniel Stowell, Director and Editor of the Papers of Abraham Lincoln at the Abraham Lincoln Presidential Library and Museum.

Keeping secrets from the enemy is vital to combatants in any war, and the American Civil War is no exception.  Union and Confederate leaders sent directions to and received reports from their subordinates over wide areas.  The telegraph made “lightning” communication between distant points possible.  Leaders who could use it effectively had a decided advantage, both on the battlefield and in mobilizing their society’s resources for war.

The simple substitution of words or letters for other words or letters is an ancient technique for keeping messages private between the sender and the recipient.  Lovers sent messages to each other in their own private codes, and diplomatic and military leaders also sent messages that messengers or interceptors could not understand.  Critical to transmitting such messages successfully was that both parties knew and understood the code and that the encoded message made it safely between them, usually by a personal courier or perhaps even by mail.  The development of the telegraph complicated the private transmission of messages, because anyone along the line of communication could tap the line and intercept the series of dots and dashes that were used to transmit messages over the wires.  In wartime, messages traveling hundreds of miles were often intercepted by enemy agents.

Anson Stager (photo from Library of Congress)

The fact that Confederates could often intercept Union messages sent by telegraph made encoding important messages critical to the success of the Union war effort.  At the outbreak of the American Civil War, the governor of Ohio asked Anson Stager, the civilian superintendent of the Western Union Company, to manage telegraph operations in southern Ohio and along its border with (West) Virginia.  Stager developed a cipher, or code, with which the governor of Ohio could communicate secretly with the governors of Indiana and Illinois.  General George B. McClellan also used the cipher when he was leading a Union army in western Virginia.  When Stager became head of the Military Telegraph Department in Washington in October 1861, the Union Army put the components of Stager’s cipher into widespread use.

The key to the success of Stager’s cipher was absolute secrecy.  Typically, fewer than a dozen people had access to any cipher.  These small books became the most important piece of property traveling with an army.  Even commanding generals and other telegraphers did not have access to the cipher code.  Large armies in the field generated thousands of telegrams, and only a minority of the most important were sent in cipher.  The cipher telegrapher had to encode and decode any message sent in cipher himself.  Once encoded, he could have another telegrapher send the message because the other telegrapher was only sending a series of words, without understanding their meaning.  Similarly, a telegrapher could receive a telegram in cipher, then pass it along to the cipher telegrapher for decoding.

In addition, the War Department used multiple ciphers simultaneously, so different armies communicated highly sensitive materials to Washington using different codes.  Only the cipher telegraphers in the War Department knew which codes were used by which armies.  If a cipher telegrapher were captured by the enemy, as happened at least once, the telegraphers switched to a different cipher to communicate with that army.

Like messages for thousands of years, Union cipher telegrams used word substitution to obscure the meaning of the message.  Stager developed code words for times of day; important political and military leaders, from both the Union and the Confederacy; cities, states, and rivers; and important military terms.  Substituting arbitraries, or code words, for key words in a message made them difficult to understand.  In addition, Stager added arbitraries for punctuation.  In Cipher No. 1, for example, “pedlar” and “Pekin” were arbitraries for a comma, and “star” was an arbitrary for the word “interrogation” or a question mark, depending on context.  “Unity,” “zodiac,” and “zebra” were arbitraries for a period.

For frequently mentioned persons, multiple arbitraries referred to a single person.  For example, in Cipher 9, used from late 1862 to mid-1864, the arbitraries for President Abraham Lincoln were “Adam” or “Asia.”  In Cipher 1, used from mid-1863 through the end of the war, arbitraries for Lincoln included “Bologna,” “Bolivia,” “Ida,” “ink,” “Irving,” “ingress,” “ingrate,” and “ingot.”  Only the cipher telegrapher would know that any of those eight arbitraries referred to President Lincoln.

The use of arbitraries in cipher messages provided a great deal of security for important messages, but arbitraries might only replace 10 to 20 percent of the key nouns and verbs in a message.  Through careful study, Confederates might have been able to decipher one or more of the Union ciphers, but Stager’s system had another feature that made cracking the Union ciphers much more difficult.

That is our next blog post!

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