The first concern of any battery, once it is in position, is to be capable of maintaining fire as long as it is called upon to do so, and whenever necessary. To be able to do this presupposes immunity from hostile fire, and, it having been found in practice impossible to secure adequate protection from determined shelling, this involves concealment, not alone from direct view from the enemy's positions, but also from his aeroplanes and observation balloons. It is comparatively easy to find some natural or artificial feature behind which to place a battery, but it is almost a life study so to disguise that battery that it will not be detected from above. Pits may have to be dug to hold the gun and its detachment, spanned by iron rails carrying a load of earth artistically planted with shrubs and flowers, the inside of a hay-stack may be torn out so that a heavy howitzer can just be manipulated in the space so formed, an innocent heap of beetroots may conceal the long graceful contour of a sixty-pounder. Yet, however careful the disguise, unless the detachments themselves hide under any cover available and remain absolutely still when a hostile aeroplane is overhead, or if by mischance the tell-tale flash of the gun betray it, suddenly and without warning the heart-gripping whirr of heavy shell will be heard, and before there is time for everybody to find the dug-outs, the battery will be an inferno of unendurable explosions and deadly flying splinters. Then, happy the battery commander whose casualties are but slight! If the battery is so concealed from the enemy's positions that it cannot be seen from them, it follows that neither can they be seen from the battery. In order, therefore, to be able to bring fire to bear upon any given point, the officer controlling the battery must have recourse to one of three expedients. He must either go himself to some point from which he can see his target, and from which he can communicate with the battery, or he must plot the position of battery and target on a map, and work on that, or he must have an observer in an aeroplane who can see the target and can communicate with him. The first of these methods is known as direct observation, and may be described as one of the most important things that the war is teaching, and the most absorbing phase of the artilleryman's life. The principles underlying the second and third are self-evident, and the details of their application too lengthy for description.