The gravity of the situation forbade experiments with hit-or-miss methods. It was imperative that no round pegs be placed in square holes. Each one of those nearly three million American soldiers had to be placed where he would be of greatest service. Some simple, quick method of distribution was needed. It was perfectly obvious that these men could not be equally good material for soldiers or officers. Out of so great a number it was reasonably certain that men could be found especially qualified to perform each one of the particular tasks which the infinitely complex scheme of organization of a modern army requires. It was in accordance with the law of probabilities that there would be contained in this mass of soldier material men highly skilled in every one of the more than seven hundred distinct and specific trades and handicrafts in which artisans were needed for the successful maintenance of the fighting forces in the field. The drag-net of the selective service system was certain to gather in its meshes men who were natural leaders and many more men who could only follow. From every city block, every crossroads hamlet, every village street would come those who could teach and those who could only learn. It was inevitable, moreover, that in this huge aggregation of human beings there would be a percentage of the wholly unteachable, the mentally stunted, fit only to be hewers of wood and drawers of water and sure to be a detriment and handicap to any military organization whatsoever. In a lesser degree the same generalizations applied to the human raw material admitted to the various officers’ training courses; even though a fairly high minimum of educational attainment was required of all candidates, there was bound to be a wide range of military value between the best and the poorest of this officer material. Psychology, the science that deals with the human mind, offered the only possible short-cut to the ultimate goal of the placement of every individual in the Army at the point where his efficiency would be greatest. The processes of the selective draft had weeded out the larger portion of the physically unfit. The draft questionnaire, as finally revised, provided for a rough preliminary classification of men according to their own estimates of themselves. But something more was needed—some system for passing the entire Army, officers and men, through a series of graduated sieves, as it were, so cunningly devised, and operated with such scientific precision as to tag, label, and index each and every one so exactly that as little as possible would be left for experience to disclose as to his qualifications for his particular part of the Army’s job.