Taking up his position at the head-quarters of the Commander-in-Chief, and keeping in close touch, also, with the Minister of War through the Chief of the General Staff, the Directeur de l'Arrière has for his special function that of securing complete co-ordination alike between rail services and road services and between the services in the Zone of the Interior and those in the Zone of the Armies. Both from the Minister and from the Commander-in-Chief he receives information as to operations projected or in progress, and as to the needs of the armies in _personnel_ and _matériel_. His business it is to see that these needs, according to their order of urgency--as further communicated to him--are supplied under conditions which shall provide for all contingencies and guard against all possible confusion or delays. He fixes, among other things, the lines of communication; he keeps in close touch with the road services, and--having, within the limit of his instructions, complete control over the railways in the Zone of the Armies--he decides on the conditions to be adopted in respect to all transport alike from the interior to the armies and from the armies to the interior. As between, also, the Minister of War and the Commander-in-Chief, he maintains a constant exchange of information concerning time-tables for military trains and other such matters. In the discharge of these duties the Directeur de l'Arrière is aided by a staff which comprises both the technical and the military elements; but he is not himself responsible for the actual working of either the rail or the road services. Railway services in the Zone of the Armies are--subject to the supreme authority of the Directeur de l'Arrière--under the control of a _Director of Railways_ who is assisted by (1) a combined military and technical staff; (2) a Line Commission for that section of the zone where the railways can still be worked by their ordinary staffs; and (3) one or more _Field Line Commissions_ ("Commissions de chemins de fer de campagne"), together with Railway Troops, for the section where military operation is necessary. In the interests of that co-ordination to which so much importance is rightly attached, the Director of Railways refers to the Directeur de l'Arrière all demands for transport that concern the railways of both the Zone of the Interior and the Zone of the Armies or involve conveyance by road as well as by rail. He also passes on to the Commissions in charge of either section of the railways included in the Zone of the Armies the orders he himself receives from the Directeur de l'Arrière in respect to such transport requirements as may concern them. Time-tables drawn up, and other arrangements made, by these Commissions are subject to his approval. He further decides as to the distribution, within the Zone of the Armies, of the rolling stock and the railway personnel placed at his disposal by the Commander-in-Chief.