Robert Townsend operated a merchant shipping business in British-occupied Manhattan before joining the American intelligence network in 1779. His commercial work provided access to docks, shops, coffeehouses and social gatherings where he could observe military activity without presenting himself as a soldier. Recruited into the system run by Benjamin Tallmadge and Abraham Woodhull, he used the cover name Samuel Culper Junior and the numerical designation 723.

Townsend gathered information on British troops, shipping, supplies and plans. His reports traveled by courier, commonly Austin Roe, to Setauket on Long Island, then by Caleb Brewster's boats to Connecticut and onward to Washington's headquarters. Codes and invisible ink helped protect the messages and the identities of the agents. The hazardous route caused frustration when information arrived too late to be useful. His letters show the limits of clandestine communication.

The network reported British counterfeiting operations and preparations that threatened the French forces at Newport in 1780. Such intelligence helped Washington judge enemy intentions while avoiding a direct attack on occupied New York. Townsend continued commercial life after the war and returned to the family home at Oyster Bay after his father's death in 1790. He kept his intelligence work secret throughout his lifetime. Twentieth-century handwriting research identified him as Culper Junior, connecting him with the surviving reports.