These closing comments from General Washington in a 1777 dispatch to Colonel Elias Dayton brilliantly summarized the instructions Washington had given Dayton: obtain secretly the enemy strength on Staten Island, together with the location and strength of their guards. And little more than a year later, Washington, like a case officer for a modern intelligence agency, instructed his director of the secret service, Major Benjamin Tallmadge, on the chief elements for gathering and reporting intelligence information; and hoped these ideas would be implemented by his special spies, codenamed "Culper," who were under Tallmadge's control.

Continuing on, Washington noted special attention should be given to the arrival and departure of naval vessels, movement and destination of troops, sizes of reinforcement, numbers of recruits for filling out the regiments. And the general wanted careful reports on the milieu of the times: "The temper and expectation of the Tories and Refugees is worthy of consideration, as much may be gathered from their expectations and prospects; for this purpose an intimacy with some well informed Refugee may be political and advantageous." Moreover, Washington continued, it would be wise "to contract an acquaintance with a person in the Naval department, who may either be engaged in the business of providing Transports for the embarkation of the Troops, or in victuelling [sic] of them."^[74]

In another set of instructions, Washington urged that his informant in New York City mix among the British officers and refugees in the coffee houses and other public places: to learn how their transports were protected against attack, whether by chains or booms to ward off fire rafts, or by armed ships. Also, he asked about the harbor fortifications, number and size of cannon, whether there were pits dug within and before defensive lines, and whether they were three or four feet deep and had sharp pointed stakes installed that were intended to wound men who attempted a night attack.^[75]

Besides advice, Washington also provided the Culper spies with invisible ink – he called it the "white ink" – for their dispatches. The use of secret fluids dates back to antiquity. Writing in the generation after Julius Caesar's reign, the poet Ovid revealed in The Art of Love: "A letter too is safe and escapes the eye when written in new milk: touch it with coal dust and you will read. That too will deceive which is written with a stalk of moistened flax, and a pure sheet will bear hidden marks."^[76]

General Washington explained to Tallmadge that he was sending all the special writing chemical that he had in phial number 1. In phial 2 was the liquid that made the white ink visible by wetting the paper with a brush. Utmost secrecy regarding these materials, Washington told Tallmadge, was indispensable. Sir James Jay, a London physician and John Jay's brother, invented the two special fluids and sent a supply to his brother and also General Washington. Early in the revolution, Sir James used the ink at the bottom of brief friendly letters to his brother and told him of the British ministry's decision to force the colonies into submission; he also wrote from London to Franklin and Deane in Paris and warned them of General John Burgoyne's intended invasion from Canada. Silas Deane had been given a supply of the precious ink by John Jay shortly before sailing for France in March 1776, and later James Jay sent additional supplies. Robert Morris told John Jay to apply the special ink on his letters to Deane.

In September 1779, Washington wrote from his headquarters at West Point and taught his director of secret service several practical techniques for Culper to use for hiding the secret messages, thus protecting the messengers who carried the dispatches. Culper should "occasionally write his information on the blank leaves of a pamphlet; on the first second &c. pages of a common pocket book; on the blank leaves at such end of registers almanacks [sic] or any new publication or book of small value. He should be determined in the choice of these books principally by the goodness of the blank paper, as the ink is not easily legible, unless it is on paper of good quality. Having settled a plan of this kind with his friend, he may forward them without risque of search or the scrutiny of the enemy as this is chiefly directed against paper made up in the form of letters."^[77]

Another method would be, Washington wrote, to write a letter on domestic affairs to his friend at Setauket, Long Island, and write with invisible ink between the lines, or on the opposite side of the page. To distinguish these letters meant for Washington, Culper could leave off the place or date (putting the date in invisible ink), or perhaps fold letter in a special manner. However, he concluded that the mode of writing in the fly leaves of books seemed the safest method to him. Perhaps recalling the capture and imprisonment of Benjamin Church, who aroused suspicions with his encoded letter in 1775, Culper apparently preferred using the invisible ink rather than the code sheet prepared by Tallmadge. Moreover, the British troops were opening all letters carried to New York, and an encoded letter always raised suspicions. His New York spies must have used the secret inks because Washington continued to urge his agents to economize in writing with the special ink because he had only small amounts.

With growing frustration, Washington wrote to Tallmadge in February 1780 and sent hard money of twenty guineas and more invisible ink for the New York agents. Culper was using the ink on blank sheets of paper and sending them by messenger: this, complained the general, was bound to raise suspicions. Rather, Tallmadge should tell him again to write in "Tory stile," describing family matters, and between the lines write in invisible ink the special intelligence information.^[78]

General Washington knew how to obtain special intelligence and, as importantly, how to mask it in dispatches. His thoughtful, thorough, and creative instructions reflected experience and practical knowledge on espionage practices, and especially secret writing. Facing an enemy that had overwhelming military power, Washington recognized the crucial necessity for intelligence and secrecy, for they promised military success and, as well, the continued independence of a new nation.