If a machine gun opens fire from the trench opposite, try to locate it through the light and sound at night, through sound and actual sight during the day. Fire a converging volley of two rounds in its direction, and repeat, but not over six rounds if unsuccessful. At the same time let trench mortars fire bombs in the same direction. 51.--His field and trench artillery fire. If enemy's artillery fires upon trenches (Cf. par. 69 ff.) AN ATTACK. THE REPULSE. 52.--A threatened raid. As has been stated (par. 15 and 22) in case enemy patrols approach, volleys of two, then of three rounds should be fired. Keep cool. Do not fire prematurely. 53.--Fire above parapet. The firing should be done over the parapet and not through the loopholes. 54.--When alarm is given. If the sentinels report that an attack is developing, every one on duty takes his post. 55.--Flares. Flares are sent up from each section. 56.--Trench Mortars. Trench mortars fire bombs with the first volley. 57.--How to repulse an attack. If the attack materializes, repeat volleys and trench mortar discharge and open fire with the machine guns. (On dark nights, in covered terrain, the machine guns should be fired with the first volley.) 58.--Use of hand grenades. Hand grenades should be thrown as soon as the enemy is within 30 yards. The grenadiers of the odd number squads should aim to throw their grenades upon the assailants while those of the even number squads should try to establish a barrage by throwing behind the assailants. 59.--Use of trench mortars. The trench mortars are aimed at the enemy's trench. 60.--Use of the machine guns. The machine guns fire directly at the assailants, with slight differences in height of aim, (knee high, waist high, etc.) according to the directions previously given to each man. 61.--Fire Control. Carefully keep fire rifle under control and avoid wasting ammunition. Never fire without aiming. If the ground ahead is flat, aim waist-high; if it slopes down, aim close to the soil; if it slopes up, aim at height of chest. 62.--Repulse with the bayonet. If some of the enemy reach the trench, dispose of them with the bayonet. 63.--Save ammunition. Cease firing and abstain from further firing as soon as the attack is repulsed. THE COUNTER ATTACK. 64.--Immediate. It should follow immediately upon the successful repulse of the attack. 65.--Counter attack formation. It should be developed in the following formation: 1st. Grenadiers armed only with a bayonet, a bowie knife, a revolver and a full stock of grenades. With them a few men with pliers for wire cutting. 2nd. Next a skirmish line of riflemen with a full supply of ammunition. 3rd. Lastly, a line of men with entrenching tools.[B] 66.--Method of advance. Proceed by short leaps making use of available protection and crawl flat on the ground in approaching the enemy's trench. 67.--Capture of the enemy's fire trench.