Furthermore, even those bodies of troops in immediate advance of which the great cavalry masses are on the move require their own cavalry, not only for the purpose of ensuring and maintaining communication with the army cavalry, but also that they may not be entirely denuded of cavalry when, as the hostile armies approach each other, the cavalry masses clear the front and concentrate towards a flank. Finally, it will not always be possible to detail portions of the army cavalry to detached forces, because it has other duties to fulfil and other claims made upon it. Thus, for example, the army of Manteuffel in the campaign against Bourbaki had at its disposal none other but the divisional cavalry.[5] The weak divisional cavalry, therefore, must be prepared to carry out all the cavalry duties which may arise from these conditions. Amongst them particular mention must be made of the outpost service, which, although shared with the infantry, imposes a heavy burden on the divisional cavalry. Any one who has once been through manoeuvres knows how great the demands of this service are, even in peace, in the exertions involved and the time expended. In war these exertions become at times considerable, if less frequent, for the critical days do not follow each other so closely as in manoeuvres. If we consider, moreover, how every cavalry undertaking has increased in difficulty owing to the greater size of modern battlefields and the improvement in firearms, it will become clear that the sphere of usefulness of the divisional cavalry, even from the purely tactical point of view, which up to now we have alone considered, is a very extensive and important one.