The portion of the Hindenburg line which the 27th and 30th Divisions were to attack had a distinctive character which might well relate its conquest to an action by such an integral force as our Second Corps, attached to another army. For six thousand yards the Saint-Quentin Canal, opened in Napoleon's time and used until the beginning of the war, runs in practically a straight line north and south under a ridge, whose crest, from the piling of the spoils of excavation, is almost as regular as an enormous parapet. The open canal being unfordable, this section, obviously inviting attack, was given particular attention in preparing the artificial defenses which the ground and the tunnel itself favored. The thickness of the earth over the stone arch was such that at no point had the largest caliber shell the slightest chance of successful penetration. In the tunnel, lighted by electricity, the number of reserves which could be accommodated was regulated by the extent of the wooden platforms laid across from wall to wall. It was said that there was room enough provided for a full division of infantry, which, while being entertained by moving pictures to while away idle hours, would be perfectly secure from any bombardment until such time as their services were required, when they had prompt egress to their places assigned for a crisis through the openings to the reverse slope of the higher irregular crest in front. It was a most comfortable and adaptable arrangement, for which the French a century ago had done the spading. On the crest in front of the tunnel, of course, none of the provisions in dugouts, traverses, strong points, and barbed wire of a thoroughgoing trench system was lacking. In front of this crest over which the main Hindenburg line ran, at a distance of a thousand yards, was another ridge, which formed the first or outpost line. Any troops who took this forward line must move down an apron in full view of the trenches of the main system, in range of its machine-guns and rifles, and under its observation for the direction of artillery fire, which of course had this apron accurately plotted. Between the two ridges, utilizing the ravines, sunken roads, and irregularities of ground, the Germans had deep communication trenches, which, with the passages out of the tunnel, further connected up the system in facilities for the swift utilization of their troops in making the most of all the details of natural and artificial advantage of a position which had on its flanks the unfordable canal. But the defenses had not been well kept up, partly as a result of the deterioration of German industry in digging, and more largely because of Ludendorff's commitment to mobile warfare by his March offensive.