Benjamin Tallmadge left teaching to join the Continental Army in 1776 and developed a dual career in cavalry operations and intelligence. A Yale graduate, he fought during the New York campaign and became an officer in the Second Continental Light Dragoons. Service at Brandywine and Germantown preceded the responsibility for which he became best known: organizing reliable information from British-occupied New York.

Beginning in 1778, Tallmadge directed the network commonly called the Culper Ring. Abraham Woodhull, Robert Townsend, Caleb Brewster, Austin Roe, and others gathered and transmitted reports through routes linking Manhattan, Long Island, and Connecticut. Tallmadge used the alias John Bolton and developed a numerical codebook. Invisible ink and compartmentalized communication helped protect identities, although secrecy and the speed of transmission could conflict. The network informed Washington about British forces and intentions rather than operating as an all-knowing modern intelligence service.

Tallmadge also commanded raids against British installations on Long Island, including Fort St George in 1780. During the exposure of Benedict Arnold's plot, he became suspicious of the captured John André and helped prevent his return to Arnold's headquarters. Intelligence work and field command thus remained connected, drawing on his familiarity with local people and geography.

After the war he settled in Litchfield, Connecticut, entered commerce, land investment, and banking, and served as postmaster. Elected as a Federalist, he represented Connecticut in the United States House from 1801 to 1817. His later business and public life extended beyond wartime intelligence. He wrote a memoir that preserved recollections of service while leaving many intelligence details understated. He died in 1835. His intelligence work depended on trust, codes, couriers, and commercial travel. Wartime networks later supported political and financial opportunities.