Stokes mortars and machine-guns were assigned important _rôles_ in the early part of the attack. The 3-inch mortars belonging to the Division, less four a brigade, to be taken forward in the attack, were to open a hurricane bombardment for three and a half minutes at "Zero." A battery of 4-inch Stokes mortars, specially attached, was to preface the assault with a bombardment of the Spanbroek salient, with two lifts, using the highly demoralizing incendiary shell known as "thermit." Six guns of the Machine-Gun Companies of the attacking Brigades were to go forward with them; the rest of the guns of these companies, with those of the 108th, the 32nd, two sections of the 33rd, and six guns of the 19th Motor Machine-Gun Battery,[32] a total of sixty-six guns, were to be employed to provide a creeping barrage beyond that of the artillery, a standing barrage on the main defences of the ridge, and fire on strong points, woods, and ravines. One section of Tanks[33] was allotted. They were not to catch up the infantry till the Blue Line was reached, and in the advance to the Black Line were to concentrate mainly upon Wytschaete. All the successive lines, with the exception of the Green, were to be consolidated, special strong points being established at such positions as L'Enfer Farm, Skip Point, and Jump Point, in the Blue Line; and Lumm Farm, Pick House, and Torreken Farm in the Black. The infantry was to start the work of consolidation; then, when the Black Line had been taken, the 121st and 150th Field Companies were to move up to work upon the principal strong points. After dusk on the evening of "Z" day, the 122nd Field Company was to move up and construct a wire entanglement along the whole front of the Black Line. Small opportunity, it will be seen, was left for successful counter-attack if the assault reached its objectives. Two contact aeroplanes were to be in the air at once throughout the battle, calling at fixed hours, by the sounding of a Klaxon horn and the firing of a Vérey light, for the signals by which the infantry was to mark its progress. The latter consisted of green flares, lit in bunches of three, and the turning of Watson fans, marked white on one side and black on the other.