Lastly, the preceding means for controlling the barrage can be employed in conjunction. That is to say, a time-table for the barrage is adhered to during the first part of the advance when the positions of the hostile lines are well known, while during the last part, when the infantry’s progress is not so regular and the ground is not so well known, each advance of the barrage may be called for by rocket, as each resistance met with is disposed of. If an assaulting battalion meets a resistance which it cannot reduce by its own means, it must call upon the support artillery for help. To do this, the artillery must halt its barrage and for an interval the time-table is not in effect. Such an emergency calls for a special action on the part of the support artillery, and also for the intervention of any other artillery at the disposal of the general. This particular action of the artillery may be called for automatically by rocket or by the other means of liaison. The rôle of the officer and N. C. O. of the artillery liaison detachment is to give the artillery the precise technical information necessary in such a case to establish its fire on a nest of resistance. This action of halting the barrage and giving the artillery a new objective is exceptional and delicate to execute. As soon as the resistance is reduced, the time-table is resumed. =Liaisons During the Attack.= The proper co-ordination of all the foreseen developments of the attack lies in a good system of liaison. There must be leadership liaison for the transmission of orders and reports, and infantry-artillery liaison for the proper co-operation of the two arms. The means of liaison in the offensive are the same as those considered in the defensive organization. The principle of their use is the same but made more difficult by the progress of the different attacking echelons. It is the duty of all leaders to foresee the establishment of liaison for the engagement in their plan of battle, and also for the prolongation of these means with the advance of the attacking troops. The means of liaison are: Telephone lines (for leadership in artillery. They are lengthened from the parallel of departure to the interior of the enemy’s position.) Signal communication (established from the enemy’s position to a central point in the rear). Rockets (precise signification of each kind laid down in orders). Carried pigeons (headquarters that are to carry these laid down in orders). Detachment of special runners (essential to be established between all units).