Although in these measures the principles for the reconnaissance may be sought, it must be clearly understood that the original allotment of zones cannot always hold good. This arrangement is only practicable and suitable so long as the opposing armies are frontally approaching each other. As soon as the directions of march form an angle with each other the conditions alter.
When information has been obtained as to the enemy's position and that the direction of his advance is not directly at right angles to our front, or if the direction of march of our own army changes, it may be necessary to make repeated changes in the zones of reconnaissance. The manner in which this can best be done is a matter which experience alone can show us. The change of zones will often be possible in conjunction with the recall of detached squadrons and the sending forward of fresh ones in a new direction, or during the relief of reconnoitring squadrons.
When the gradual advance of the hostile army takes place and the army cavalry endeavours to clear the front and to draw away to a flank, or when the columns of both armies group themselves for the tactical decision and concentrate more or less from their march formations, the allotment of zones must utterly fail.
An allotment of zones, also, cannot always be recommended, that is to say, not where it can be foreseen that it cannot be carried into operation. Such a case might happen if an enemy moved across the front on a more or less distinct flank march. The reconnoitring squadrons would, perhaps, in such a case be better employed in keeping touch with the various groups of the hostile army than by tying themselves down to a systematic reconnaissance in zones.
The conditions of war are everywhere so changing and full of movement that a single concrete scheme will never suffice, but each case must be judged upon its own merits. The allotment into zones, therefore, laid down in the "Field Service Manual" must be regarded as but a foundation for the methods to be adopted, and will perhaps only attain its full effect during the first concentration of opposing armies, when the hostile groups deploy along a land frontier on a wide front. During operations the original scheme must of necessity be subjected to continual alterations and transformations.
Let us now further consider the relief of reconnoitring squadrons. It is out of the question that such squadrons should remain continually in touch with the enemy. Such a procedure would very soon paralyse the strength of men and horses. The relief, however, cannot, naturally, be arranged and carried out at any given moment. It requires preparation, as the whole patrol system must be drawn in and replaced by a fresh one. The relief will doubtless best take place after a great tactical crisis. At such times the reconnoitring squadrons will partly have been driven back on to the cavalry mass, and partly will be in position with their patrols near them in flank and rear of the enemy, whence they can be comparatively easily brought in. A great tactical decision also which creates a new situation demands fresh measures for reconnaissance and a different arrangement of the reconnoitring organs. Whether it will then be possible to mathematically divide the ground into sections need not here be decided.
Under certain circumstances it will be advisable to detail reconnoitring squadrons to watch the various groups of the hostile army. If we take the campaign of 1870 as an example of a concrete case, the battles of Spicheren, Mars la Tour, and Gravelotte afforded natural periods for the relief of reconnoitring squadrons and the fresh allotment of reconnoitring zones for the First and Second Armies, and later the battle of Sedan. For the Third Army, first of all, the battle of Wörth. Cases may of course occur when the reconnoitring period between the battles is too long, and a relief becomes necessary in the interim. The case of the Third Army is a good example of this.
A reconnaissance from Wörth to Sedan could never have been carried out by the same reconnoitring squadron. A relief was absolutely necessary. According to my judgment, the best time for this would have been the days during which the great wheel of the Third Army towards the north was completed. During these days fresh reconnoitring squadrons would have had to be thrown forward in the new line of march, while those which had advanced in the original direction could, according to the situation, have been gradually drawn in. Strong patrols would have been sufficient in that direction.
In any case it is clear that the question of the relief of reconnoitring squadrons is extremely important and cannot be solved by routine. It is a matter for consideration whether it would not be of advantage for the "Field Service Manual" to touch on these questions as well as on the circumstances under which a departure from the system of allotment of zones might be desirable. I am inclined to think this desirable, as otherwise the extremely practical dispositions therein laid down are apt to lead to a lifeless formalism.