Some of our officers and men had met German machine-gun practice in open warfare in the Château-Thierry campaign and at the British front. As others knew it only under the limitations of trench warfare, the resistance which they now must face was familiar to them only through instruction. The German machine-gunner, having learned as the survivor of many battles the art of self-preservation at his adversary's expense, would wait all day and all night and even longer without a shot, until his target appeared in the field of fire assigned to him; wait as a Kentucky feudsman waits behind a rock for his enemy to appear on a road. Each gun was only one in a well-plotted array covering all the avenues of approach which any attacking force must follow. The guns disposed in front might precede or wait on the guns in flank in opening fire. There was nothing new or wonderful in this arrangement. Any soldier with a sense of ground and of natural combative strategy could work out a plan of interlocking fire; but the discipline and the training requisite to its proper execution, and the stubborn phlegmatic bravery which sticks to a machine-gun to the death, are not to be found at random on any page of a city directory or social register. The fact that a gun had begun firing did not mean that it could be immediately located. Sometimes when light conditions were right the flash was visible, unless the gunner had hung a piece of bagging, through which he could aim, to conceal the flash. The direction of the fire might be judged somewhat by sound, and also by observing the spits of dust in the earth or on the wall of a building. Judgment on this score was affected by the proximity of the passing bullets to the observer's person. The more machine-guns were firing from different angles, the more difficult it was to locate any one of them by either method; and the more influential the human element. In the midst of their fire imagination easily multiplied the number of guns, which is one of the moral effects of their use. When a gun was located, the gunner might slip back behind the crest of a ridge, or he might have moved as a precaution, before he was located, to another position which had been chosen as his next berth, with pit and camouflage in readiness.