It is possible, therefore, that the first step only may be taken; i.e., that the procedure for the attainment of a particular assigned objective may be determined for the sole purpose of making provision against a contingency, at that particular time merely an obscure probability. Or, as may frequently be the case during peace, the procedure may terminate, for the time being, with the completion of the second step. In such cases, certain of the necessary military operations are worked out in the desired detail as a provision against future possibilities, are listed, and filed for reference as needed. Parts II and III, which follow, deal primarily with the solution of those problems of the naval commander which require familiarity with the entire process, i.e., all of the four steps given above. For simplicity of presentation, the procedure is described throughout from the mental standpoint of the same commander. The arrangement of subject matter conforms to this basis. The several types of problems, classified according to the source of the incentive (page 79), are discussed in connection with the appropriate step. When a problem typical of a previous step arises during the process, the sequence of steps is interrupted thereby, but is resumed by a mental return, on the part of the commander, to the proper earlier step. The First Step The mental procedure distinctive of the first step (more fully discussed in Chapter VI) deals with the usual case where a commander becomes acquainted with the nature of his assigned objective through receipt of a directive from his immediate superior, ordinarily in the form of an assigned task or assigned tasks. In the discussion of the first step, this most likely type of problem is chosen for description, i.e., the one where the motivating task (see page 80) comes directly from the immediate superior. For purposes of reference, this problem may conveniently be termed a basic problem. In such a case the original situation which gives character to the problem may be similarly referred to as the basic situation. The full solution of a basic problem always involves a basic estimate of the situation, a basic Decision, a basic plan of operations, and one or more basic directives. It may, as will be shown, also require certain additional directives. The military Estimate of the Situation, based on the natural mental processes (pages 19-20 and 43), is introduced in the first step. The reason for making such an Estimate is to provide a basis for a plan to accomplish the assigned task. The Estimate constitutes a systematic procedure for selection of a correct objective (or objectives), suitable to the appropriate effect desired, feasible of attainment, and acceptable as to the consequences involved in its achievement. The selection of such an objective or objectives involves, incidentally (see page 44), the determination, in the proper detail, of the action required.