On the 22nd August the 179th Tunnelling Company, R.E., arrived in the area and relieved the French engineers. It had by this time become evident that a very considerable effort would be necessary to check the enemy's mining if it was to continue possible to hold the existing front-line trenches. The 179th Tunnelling Company had only a strength of 300 men with which to take over from the 500 men which the French had employed in the sector. It was therefore decided to reinforce the tunnellers by attaching to them infantry who in civil life had been skilled miners. Sixty miners from each infantry brigade were accordingly added to the tunnellers. The efforts of the tunnelling company thus reinforced, by dint of working continuous shifts day and night, proved equal to the task, with the result that superiority as regards the mining situation ultimately passed to the British. It was, however, only after a severe struggle that this result was obtained. The discharging of mines and of camouflets--small discharges used for blowing in the opponent's galleries--were almost of daily occurrence. Mine warfare played so large a part in the trench warfare of 1915, 1916, and 1917, and so affected the daily life of the soldier in the trenches, that a description of what it means to those engaged in it may not be out of place. In the first instance, success in mine warfare is dependent on the tunnelling company. By their efforts it is determined whether our troops are to be blown up by the enemy, or whether it is the enemy who is to meet this fate. To secure protection for the troops listening galleries have to be driven at various points along the front, so that the enemy's galleries can be located by sound, and the element of surprise can then be eliminated. The tunnellers who listen in these galleries are equipped with instruments by which the enemy can be heard working. If he is close, he can be heard by the ear alone. In chalk, a good medium for the carrying of sound, he can be heard working, without the aid of instruments, many feet away. If he is heard still using picks or shovels, it is known that he has not driven his gallery as far as he intends, and that there is therefore no immediate prospect of his blowing. If, on the other hand, he is heard tamping--_i.e._, packing in his explosive--it is known that his work is nearly completed, and that his mine will in a few hours be ready for exploding. In the latter case two alternatives are available, either of which may be adopted to protect the troops from the effect of his blowing. First, if we have a gallery sufficiently close to his, we may blow a small mine or camouflet, designed either to destroy his gallery or so to disintegrate the soil by the explosion as to make further tunnelling impossible. If a camouflet is impracticable, the only other alternative is to evacuate the area which it is estimated will be affected by the explosion.