The necessity for movement may be an important consideration in determining possible or likely theaters of operations. Where transportation between two or more positions within a certain area is essential to the successful conduct of a war, the area which includes the routes between these positions, or a portion of such routes, becomes at once a possible or likely theater. Such an area may be normally within the control of one or the other of the belligerents, or the control may be in dispute. Certain of the positions themselves may belong to neither of the belligerents. The area itself may be a land area, or a sea area, or a combination of the two. It may be an area which borders upon the sea, or an island area. In any case, the air is a common characteristic. The movement of a force is properly regarded, not as an even flow, but as a series of steps from one position to another. The movement may or may not be continuous. Pauses are usual, their occurrence and duration being a matter dependent upon circumstances and calling for the exercise of sound professional judgment. Intermediate positions may be utilized, successively, so as to facilitate occupancy of the final position which is the goal of that phase of operations (page 56). This procedure often effects an ultimate saving of time. In many cases, other advantages also may accrue. The foregoing considerations are applicable to changes of position whether in the direction of the enemy, toward a flank, or to the rear. Flanking maneuvers and retrograde movements, both sometimes profitably employed to decoy the enemy, may frequently be utilized to gain advantageous relative position. The proper objective of each is the maintenance of a favorable situation, or the alteration of an unfavorable one, either locally or with reference to the larger phases of operations, through measures involving apportionment of fighting strength, or obtaining advantages of position, or retaining or gaining freedom of action. Combinations of forward, flanking, or retrograde movements are frequent in war, the skillful combination of the offensive and the defensive (see page 75) being no less applicable to the problem of relative position than to the other elements of a favorable military operation. Procedure for Determination and Selection of Advantageous Relative Positions. Since the various positions to be occupied become physical objectives for the time being, their proper determination and selection are governed by the same considerations which apply to physical objectives (see page 55 and following). Thus, it becomes necessary to consider, first, as to suitability, whether the position, once gained, will permit the attainment of the appropriate effect desired. Secondly, consideration is required as to feasibility. Are the available means adequate to gain or to maintain such position? In answering this question, due regard is paid to opposing means and to the characteristics of the theater.