CO-OPERATION.--"Co-operation when in contact with the enemy is no easy matter to bring about. There are, however, three means of overcoming the difficulty: constant communication between the units; thorough reconnaissance of the ground over which the movements are to be made; clear and well-considered orders" ("The Science of War"). Each commander who issues orders for Attack or Defence should assemble his subordinate commanders, if possible in view of the ground over which the troops are to operate, explain his orders, and satisfy himself that each subordinate understands his respective task. "Combination depends on the efficiency of the chain of control connecting the brain of the commander through all grades down to the {36} corporal's squad; on the intelligence of subordinate leaders in grasping and applying the commander's plans; on the discipline which ensures intelligent obedience to the directing will; and on the mobility which gives rapid effect to that will, and permits advantage to be taken of fleeting opportunities. Every fresh development in the means of transmitting orders and information rapidly, permits of an extension of the commander's influence, and makes more perfect combination possible and over wider areas" (General Sir E. B. Hamley). Even when, and particularly when, forces are engaged in battle, reconnaissance must be carried on and information gained must be communicated at once. It will frequently happen that a suitable moment for the decisive attack, or decisive counter-stroke, will be found only after long and severe fighting. Systematic arrangements for obtaining, sifting, and transmitting information throughout the battle are therefore of the highest importance. Information must be gained not only by troops and aircraft actually engaged, but by supports and reserves, who will often be able to see what is invisible to the forward troops. In such cases, more than in any other, information must be communicated at once. By intelligent observation superintending commanders can co-operate with one another, can anticipate situations as they develop, and decide at the time what steps will be necessary to meet them. A general reconnaissance will be in progress during every modern battle by observers in aircraft and in observation balloons. In addition, local reconnaissance by means of patrols and scouts will usually discover an opening that might otherwise be lost, and may warn a commander of an intended movement against him, which might otherwise develop into a disagreeable surprise.