It will seldom be possible to make much use of machine guns with the advanced guards, as mountaineers usually oppose the advance by bands of skirmishers who fire from the cover of rocks and scattered sangars, and while affording a bad target to the machine gun, can quickly put it out of action by concentrating their fire upon it. They are also unsuitable for piqueting the heights, on account of the difficulty of getting them into position and of rapidly withdrawing them again. They are, however, very useful to strengthen small fortified posts on the lines of communications, and for the defence of camps by night, being trained by day and the sights prepared as suggested in Chapter VII., page 150. Callwell says: “It is a good plan, if night attacks are at all probable, to train guns and machine guns by daylight upon points where the enemy may be expected to mass, or from which assault is to be anticipated. _This was done at the defence of Chakdara in 1897 with excellent results._” Machine guns are invaluable to the rear guard of a force retiring, which is an exceedingly difficult undertaking in mountain warfare, because hillmen invariably await this opportunity to swoop down and make a vigorous attack. The very nature of the operations necessitates frequent retirements. Callwell says: “Columns have to visit outlying valleys for punitive purposes, and must then rejoin the main body; and even when penetrating into the heart of a hostile mountain district, the rear of the army, as it passes successively the homes of different tribes and clans, draws these down upon it, and, as a result of the general direction of its march, retires before them.”