Communication and the Culper Spy Ring

The American spies needed an efficient way to communicate without the British knowing what they are up to. This led to the usage of ciphers, invisible ink and other special methods of communication. 

John Jay and Arthur Lee devised dictionary codes in which numbers referred to the page and line in an agreed-upon dictionary edition where the plain text (unencrypted message) could be found. This became one of the most commonly used ciphers of the time.

In 1775, Charles Dumas designed the first diplomatic cipher that the Continental Congress and Benjamin Franklin used to communicate with agents and ministers in Europe. Dumas's system substituted numbers for letters in the order in which they appeared in a preselected paragraph of French prose containing 682 symbols. This method was more secure than the standard alphanumeric substitution system, in which A through Z are replaced with 1 through 26, because each letter in the plain text could be replaced with more than one number.

The Culper Spy Ring used a numerical substitution code developed by Major Benjamin Tallmadge, the network's leader. The Ring began using the code after the British captured some papers indicating that some Americans around New York were using "sympathetic stain." Tallmadge took several hundred words from a dictionary and several dozen names of people or places and assigned each a number from 1 to 763. For example, 38 meant attack, 192 stood for fort, George Washington was identified as 711, and New York was replaced by 727. An American agent posing as a deliveryman transmitted the messages to other members of the Ring. One of them, Anna Strong, signaled the message's location with a code involving laundry hung out to dry. A black petticoat indicated that a message was ready to be picked up, and the number of handkerchiefs identified the cove on Long Island Sound where the agents would meet. By the end of the war, several prominent Americans—among them Robert Morris, John Jay, Robert Livingston, and John Adams—were using other versions of numerical substitution codes.

A picture of Anna Strong, the lady who hung up laundry to signal to the Culper Spy Ring.

The Patriots had two notable successes in breaking British ciphers. In 1775, Elbridge Gerry and the team of Elisha Porter and the Rev. Samuel West, working separately at Washington's direction, decrypted a letter that implicated Dr. Benjamin Church, the Continental Army's chief surgeon, in espionage for the British.

In 1781, James Lovell, who designed cipher systems used by several prominent Americans, determined the encryption method that British commanders used to communicate with each other. When a dispatch from Lord Cornwallis in Yorktown, Virginia, to General Henry Clinton in New York was intercepted, Lovell's cryptanalysis enabled Washington to gauge how desperate Cornwallis's situation was and to time his attack on the British lines. Soon after, another decrypt by Lovell provided warning to the French fleet off Yorktown that a British relief expedition was approaching. The French scared off the British flotilla, sealing victory for the Americans.

The Culper Spy Ring was also a major factor in the usage of these types of code. It was created in 1781 by a young cavalry officer named Benjamin Tallmadge, starting out as a small group of men and women and finishing as one of the greatest spy groups of all time. They were able to collect key information through very simple means, such as hanging laundry up in a specific manner (Anna Strong). Furthermore, they were able to collect very precise naval information, as well as locations where British fortifications were located. Because of their great usage of secret communication mathods, only a few of the members were caught. One of their greatest successes was when they uncovered British plans to ambush the French army in Rhode Island, and they successfully stopped the Franco-American alliance from being damaged or destroyed. They have also been credited with uncovering information involving the correspondence between Benedict Arnold and John Andre.

An example of a cipher employed with secret letters.