If the situation is to be cleared up by fighting, fire action must be employed, and as soon as this occurs, whether on the part of the enemy or oneself, a gradual employment of force is not only no disadvantage, but is demanded by the circumstances. For at first the fight must be carried out from depth; the Napoleonic "Je m'engage et puis je vois"[32] holds good; one's own main force will only be engaged when the strength and intentions of the enemy become in some measure known. It will, however, be advisable in all cases to keep a strong reserve in hand until prepared to advance to a well-considered and planned attack. The passage of defiles, also, is scarcely likely to be undertaken in serious war in the manner so often seen at manoeuvres. Here the chief matter for consideration is generally to keep one side as far from the defile as possible, in order that the passage of the other may be possible. Such tender solicitude is scarcely to be expected of a real enemy, and it will, I opine, scarcely occur to anybody in war to attempt a defile without preparation, and to advance on the farther side against an enemy whose strength, as is generally the case in war, is unknown, thereby running the danger of being thrown back on the defile and of suffering enormous loss. Such a danger, to which the whole force is exposed, would certainly only be incurred when the gravest necessity compelled. What the Regulations say in this respect (434)[33] has, to my mind, but a limited practical significance. Such directions would only be followed if the enemy were known to be still far distant and approaching, where there is time and space sufficient, and where the force is considered to be at least a match for the enemy. Even then, preparations should be made for a possible retirement. In all other cases, however, a defile on the far side of which the enemy is supposed to be will only be crossed when the ground for deployment on the far side is at least commanded with fire in such a way that the enemy will not be able, in case a retirement becomes necessary, to pursue right into the defile. It will therefore generally be advisable to throw forward a few squadrons at a rapid pace across the defile in order to occupy with dismounted action strong points on the far side, from which the foreground can be covered. This will secure the passage of the main body and arrest any possible pursuit. It will often be advantageous to provide such squadrons with machine-guns. Artillery can most suitably come into action on the near side of the defile, so that it may be able to cover the country on the far side with its fire. Even if a defile occupied by the enemy has been captured by fire action it is advisable, before the main body crosses it, to secure a few strong points in the foreground, in order to secure the passage against counter-attack by the enemy's reserve.