While gas has proved very effective under certain circumstances--and almost decided the fate of Calais early in 1915--yet it is obviously dependent upon the weather and especially the wind. Even if the direction of the wind is correct for the use of gas, the kind of wind may not be suitable at the moment. The wind must not be high nor squally, but needs to be low and gentle, just sufficient to carry the gas across to the opposing trenches without dissipating it on the journey. Then again it must be remembered that it can seldom reach the gunners who may open up intensive fire on the trenches from which it is being liberated, burst the drums and make the place untenable. Of course all the men who are employed in liberating gas should be warned to have their helmets in position to guard against these emergencies, and also against leaks in the drums. Gas masks must be tested daily to see that they do not admit any of this deadly poison. In addition to these preparations, a good many reconnaissance parties must be sent night after night out into No Man's Land to map it thoroughly, place directing boards there, dig small saps to facilitate an advance, and learn the condition of what remains of the enemy wire. This work is difficult and dangerous, and must be given to trustworthy, brave, resourceful men. For it must be remembered that the enemy will probably come out into this neutral territory at night to try and learn the plans of the opposing side, just as they are trying to learn his plans. Many bloody conflicts have taken place out there under cover of darkness when the patrol from one side has entered into conflict with the patrol from the other. Those in charge of the attack will arrange that at a specified time the bombardment will cease, and the men leap over the parapets. This time is usually arranged for, say, one minute after six, or thirteen minutes after eight--some time which the enemy cannot guess accurately. During the final awful ten minutes, the finishing touches are given to rifles and bombs and revolvers. Then exactly at the appointed time the electric buzzers in the trenches sound the signal to advance. The first man over the parapet is always an officer. Unlike the Germans, we do not drive our men but expect them to follow us, and this accounts in part for the very severe casualties that have been suffered by British officers.