Stuart, the earliest reliable biographer of Hale, in writing of spies says: "The exigency of the American army which we have just described, would not permit the employment, in the service proposed, of any ordinary soldier, unpracticed in military observation and without skill as a draughtsman,--least of all of the common mercenary, to whom, allured by the hope of a large reward, such tasks are usually assigned. Accurate estimates of the numbers of the enemy, of their distribution, of the form and position of their various encampments, of their marchings and countermarchings, of the concentration at one point or another, of the instruments of war, but more than all of their plan of attack, as derived from the open report or the unguarded whispers in camp of officers or men,--estimates of all these things, requiring a quick eye, a cool head, a practical pencil, military science, general intelligence, and pliable address, were to be made. The common soldier would not answer the purpose, and the mercenary might yield to the higher seductions of the enemy, and betray his employers." During the war with the French and Indians, American officers had learned the need of trained men who could keep the commanders informed both of the movements and of the plans of the opposing forces. Washington had learned this unforgetable lesson in Braddock's campaign, and, as full commander and wholly responsible not only for the immediate safety but for the future success of his little army, he realized the necessity of obtaining the most accurate information possible. A corps collected from the best men in the army was organized, and its command was given to Lieutenant Colonel Thomas Knowlton. He had gained experience as a ranger in the French and Indian War, and was noted for his coolness, skill, and bravery at Bunker Hill. One hundred and fifty men and twenty officers were considered sufficient for the work assigned to this special corps, known as Knowlton's Rangers. They were divided into four companies. Two of the captains of these men were chosen from Knowlton's own regiment; the other two--one of them Nathan Hale--were from other companies. There can be little doubt that Nathan Hale was proud of his enrollment in this brave corps. After Hale's services were ended, one brief record remained of "moneys due to the Company of Rangers commanded late by Captain Hale." After the 1st of September, about which time this company of Rangers was organized, it was constantly on duty wherever its services were required, and one can easily imagine Nathan Hale's enthusiasm in his enlarged duties. Knowlton spoke to some of his officers of the wishes of the commanding general for some one to enter upon this special secret service,--wishes that so appealed to Hale that he at once seriously considered offering himself for the hazardous undertaking.