Marching in column of files is not as easy as in line on open ground. Remember good artillery is pretty accurate in getting direction. Most shots will be at the head of a column and if at the head of one, another on each side is included in the burst. Direction is much easier to get in artillery fire than exact fuze setting in the case of a moving target; this is another reason against the squad column, the target is deeper and thus slightly improves the chances of the artillery. This formation not only has no advantage on open ground, in an advance under artillery fire, but does have disadvantages. [Sidenote: Platoon columns] Platoon columns. In average terrain this formation will be more used than any other. The distance between these columns is great enough so that a shrapnel bursting between two may entirely miss both; it also permits a more or less erratic or zig zag course to be followed. Each column is lead presumably by a more intelligent and better instructed man than in the case of the squad. These columns should never be on the same line but echeloned as explained for the skirmish line. In most terrains there are little hills, clumps of trees, buildings and other cover of the same general kind. Platoon leaders must while keeping generally within their own zones of advance, rush from one cover to another where it is offered and, where cover is wanting, vary the pace and avoid advancing in a straight line. Properly done this formation is one of the best. No time is lost, the columns are far enough apart to allow of advantage being taken of all the cover afforded, and the target is not, on average terrain, too vulnerable. It is not so good on flat open plains and it should not be used on such ground if the artillery fire is very oblique to the line of advance. This form of advance requires that platoon leaders understand the theory and also requires much practice on different sites to give platoon commanders facility in leading and skill in taking advantage of the cover offered. This is one of the things in which captains should give instruction during the indoor season with the aid of the sand table. In addition outdoor practice is most necessary. When this formation is adopted platoon commanders should know, if possible, before starting where line of skirmishers is to be formed. [Sidenote: Successive thin lines]