_He will select positions for the Artillery_, in consultation with the commander of that arm, the objects in view being: to command lines of approach so that the assailant may be shelled and forced to deploy early and so to indicate his plan of attack; to delay the advance; to combine with the infantry in the close defence of the main position; to support local counter-attacks; to destroy hostile batteries by counter-battery work; and to combine eventually in the Decisive Counter-Attack. The increased mobility of guns of the heaviest calibre owing to motor traction, and the increased defensive power of the protective quick-firing small arms, enable guns to be placed close behind the infantry firing line without undue risk of capture. _He will divide the position into sectors_, each garrisoned by a distinct unit, under a definite commander. The mutually supporting tactical points (farmsteads, villages, woods, ridges, knolls, etc.) will usually be held in groups, under group commanders, with definite subordinate commanders, and the group commander will probably control the local reserves of that group, with which he can assist any of the units in times of need. The units from which such groups are formed will usually be complete sections. _He will decide the position of the General Reserve_. This will be the locality best suited for the advance to the decisive counter-attack, if it is to be delivered from a distance; or near the point where the enemy's decisive attack is expected, if it is intended to hurl the General Reserve into the flank and rear of the enemy's main {95} attack while it is heavily engaged with the troops holding the position. As surprise is essential to success, the position of the General Reserve should be concealed as long as possible. The position of the General Reserve will depend upon the ascertained intentions of the enemy. At the _Second Battle of the Somme_ (March 21, 1918) the intentions of the German commander were ascertained during the first day's fighting. "As by this time (_i.e._ the evening of March 21) it had become clear that practically the whole of the enemy's striking force had been committed to this one battle, my plans already referred to for collecting reserves from other parts of the British front were put into immediate execution. By drawing away local reserves and thinning out the front not attacked, it was possible to reinforce the battle by eight divisions before the end of the month" (Sir D. Haig's Dispatches).