The fortifications along the front of the Fifth Army were of various degrees of strength, depending upon the nature of the ground and upon the time that it had been in British possession, the north being stronger than the south. The Oise, which had been looked upon as an obstacle, and the presence of which had seemed to justify the extraordinarily long sector held by the Third Corps, had to some extent dried up and had ceased to be a real protection. In the main, the defences consisted of a forward line, a chain of small redoubts, each with four machine-guns and all connected by posts; a battle-line which was strongly wired and lay about 3000 yards behind the forward line; and a rear zone, the fortifications of which were not complete. If anything were wanting in the depth of the defences it has to be remembered that we are speaking of a vast tract of country, and that to dig a serviceable trench from London, we will say, to Guildford, furnishing it with sand-bags and wire, is a mighty {82} task. There were no enslaved populations who could be turned on to such work. For months before the attack the troops, aided by the cavalry and by several special entrenching battalions, were digging incessantly. Indeed, the remark has been made that their military efficiency was impaired by the constant navvy work upon which they were employed. There is no room for criticism upon this point, for everything possible was done, even in that southern sector which had only been a few weeks in British possession. Before beginning to follow the history of March 21, it would be well to describe the position and number of the reserves, as the course of events depended very much upon this factor. Many experienced soldiers were of opinion that if they had been appreciably more numerous, and considerably nearer the line, the positions could have been made good. The three infantry divisions in question were the Thirty-ninth, which was immediately behind the Seventh Corps, the Twentieth, which was in the neighbourhood of Ham, and was allotted to the Eighteenth Corps, and the Fiftieth, which was in general army reserve, and about seven hours' march from the line. The First Cavalry Division was in the rear of the Nineteenth Corps, while the Second Cavalry Division was on the right behind the Third Corps. The Third Cavalry Division was in billets upon the Somme, and it also was sent to the help of the Third Corps. Besides these troops the nearest supports were at a distance of at least three days' journey, and consisted of a single unit, the Eighth Division.