As the number of guns engaged is always small, concentration of fire is especially desirable, even when the ground does not admit of concentration of guns. Mountain warfare involves frequent exposure to sudden attacks. Guns should therefore always have a strong infantry escort; but the fact of having an escort should not prevent the commander from having a lookout posted on his exposed flank. Choice of positions and taking advantage of ground are exceptionally difficult, and need special training, quickness, and constant practice. It is not always easy to secure a ready supply of ammunition. Firing should therefore be confined, as a rule, to the most effective ranges. It is a waste of ammunition to fire at long ranges. Only as many ammunition-mules as are immediately required should be brought up to the battery; the remainder, with relief-mules, etc., should be kept under cover in rear. Care must be taken to equalize the loads of ammunition-mules. The position of the battery in the column, when there is a probability of being attacked, should never be too far to the front, but sufficiently so to come into action as soon as the advanced guard is engaged. It should march after the second company of the main body if the advanced guard consists of only one company, or after the first company if only two companies are in the advanced guard. The battery ought never to be broken up unless under exceptional circumstances, such as there being insufficient space for the guns in line. In such cases the chiefs of platoon should keep up communication with the battery commander, who directs the fire generally. This breaking up of the battery does not refer to small isolated columns to which platoons only may be attached. Placed in position sufficiently far to the front to support the troops with which it is co-operating, without endangering the guns, any further change of position, excepting at the critical moment of pursuit or retreat, should not be made without some very strong reason. If a second position becomes necessary, the battery commander should first assure himself that he can reach it in time to carry out his idea, and without the liability of experiencing heavy loss. Before coming into action the battery is divided into two lines, viz., the first line, consisting of the six guns and the twelve ammunition-mules, and the second line, consisting of the remaining ammunition-mules and spare material-mules of the battery. =The Supply of Ammunition is kept up as follows=: In action the boxes of the first ammunition-mules are unloaded and placed in rear of the guns, or, if the ground permits, in rear of the flanks of the battery. The unloaded mules are placed under cover near the remaining ammunition-mules of the first line, fifty or sixty yards in rear of the line. The second line, under the first sergeant, is three or four hundred yards in rear of the first line and under cover.