By means of the chain of command, a commander is enabled to require of his immediate subordinates an expenditure of effort which, in the aggregate, will ensure the attainment of his own objective (page 3). He thus assigns tasks to his immediate subordinates, whom he holds directly responsible for their execution without, however, divesting himself of any part of his initial responsibility. The accomplishment of each of these assigned tasks will involve the attainment of an objective, necessarily less in scope than that of the immediate superior but a contribution to the attainment of the latter. The character and magnitude of the objective of the highest echelon involved will have considerable bearing upon the number of echelons required for its attainment. Whatever the number, a commander on a particular echelon occupies the position of an immediate subordinate to a commander on the next higher echelon, and that of an immediate superior with relation to a commander on the next lower echelon. Within these confines, authority is exercised and accomplishment exacted, both to the extent calculated to ensure unity of effort. There may frequently be found two or more commanders occupying coordinate positions on the same echelon, all with the same immediate superior, and all charged with loyalty to him and to each other in the attainment of a common objective. In no case, however, will a commander be directly answerable to more than one immediate superior for the performance of the same duty. Thus is fulfilled the requirement that the command, although relatively narrower in scope as the scale is descended, be reposed in a single head. The experience gained and the knowledge acquired during early service on the lower echelons provide a basis for later expansion of viewpoint, a better understanding of the position occupied by the subordinate and of the obligations of higher command, including its dependence on subordinates. As the echelons of command are ascended, the details involved become more and more numerous, because of the increased scope of the problems. On the higher echelons, therefore, staff assistance is provided so that the commander may be left free to consider matters in their major aspects. The staff of a commander is not, however, a part of the chain of command; its members, as such, exercise no independent authority. A chain of command is not created by the subdivision of the officer corps into grades on a basis of relative rank. Such subdivision is for the purpose of classification from the standpoint of potential competency and capacity for responsibility, and carries no authority to command by virtue of rank alone. Organization, systematized connection for a specific purpose, is first necessary.