Spying techniques in the American Revolution incorporated letter-writing cryptographic devices such as ciphers, as well as coded, hidden and masked communiques. Spying also relied on networks of trusted informants as well as message interception and decryption efforts.
The Culper Code Book, used by a spy ring of the same name based in New York City during the American Revolutionary War, used a substitution cipher that consisted of several hundreds of common words and fake names. The Culper spy ring used the code to transmit information about British military plans, fortifications and troop movements in the New York area during the war. The group was led by Major Benjamin Tallmadge, who worked to recruit loyal friends as informants despite the threat of capture and execution at the hands of the British.
The chemist and physician John Jay created a form of invisible ink for the Revolutionary army to use during the course of the war. It was a solution made out of tannic acid, which General Washington urged his men to use in the blank portions of innocuous pamphlets, lettters or books.
Additional spy techniques involved hiding letters in common objects. Notably, the British spy Daniel Taylor was intercepted carrying a message in a small hollow silver ball. He hastily swallowed the item to avoid its capture, but was forced to regurgitate it and was later executed.