The large trench mortars are commanded by an artillery officer who keeps himself constantly in liaison with the commander of the center of resistance. He consults the latter on the location of his mortars and especially upon their use. He also reports to the commander of the center of resistance all orders he receives from his artillery chief. This artillery officer always works in co-operation with the chief of his area, who in turn gives him all necessary information and help. Especially does the mortar commander require help for the supply of ammunition. Artillery Support in a Sector =Composition of the Artillery Support.= The light artillery of this sector is not directly under the command of the Division Commander. The Commanding Officer of the light artillery, usually a Colonel, in cooperation with the chief of the sector, divides it into different parts, assigning one to each of the centers of resistance. This artillery is called support artillery. As we shall see later this practice is usually the same in the offensive. The amount of artillery allotted as support depends upon the tactical situation, in other words, the activity of the enemy. In the Verdun and Champagne offensives the disposition of light artillery was the same in principle as that for the defensive, that is to say, one troop of artillery consisting of 3 batteries was assigned to each infantry battalion. The general use of this artillery, is: (_a_) To protect the infantry with barrage fire. (_b_) Prosecution of destruction of the enemy’s personnel and works. =Tactical Liaison between Infantry and Orderly.= To carry out its functions, the artillery support must be in perfect liaison with the infantry, and only when this is done is co-operation of the two arms possible. This liaison is obtained by the following five means: (_a_) Organization of Leadership:—For the full co-operation of the infantry and artillery, the latter is not kept entirely independent, but is divided and assigned to infantry unit. Each chief of sector and each chief of center of resistance knows what artillery must support him if he needs it. The commander of the artillery support is not exactly under the command of the infantry chief of area, but he is at the latter’s disposal for certain calls for support fire. The proper co-operation of these two officers will give efficient results.