ECHELON, in military tactics and drill, a formation of troops composed of successive and parallel units facing in the same direc tion, each on a flank, and to the rear of, the unit in front of it (Fr. from echelle, ladder). The disposition of the whole thus resembles the steps of a staircase. To form echelon from line, the units forming the line move off, each direct to its front, in succession, so that when the formation is completed the rightmost body, for example, is farthest advanced, the one originally next on its left is to the left rear, a third is to the left rear of the second, and so on. The word is also used more loosely in tactics and strategy to express the successive parts of a unit or force, e.g., forward, reserve or rear echelon, irrespective of distances and relative positions; and in military organization to indicate parts of the headquarters organization which are left in rear of the fighting zone.