Lord Haig in his Despatches has revealed that, not being able to hold all his extended front in adequate strength, having to take risks somewhere, he took them on the front of the Fifth Army, where there was most elbow-room, and where loss of ground was likely to have least serious effects. It had become more and more apparent that defence in depth offered the best means of checking and breaking up an advance, and it had been laid down by G.H.Q. that all preparations must be based upon that system. Unfortunately, with the slender forces at the disposal of General Gough, defence in adequate depth implied a very shadowy defence in breadth. The system of defence of divisions in line comprised a Forward Zone and a Battle Zone. The object of the former was to withstand a minor attack, and to check and, so far as might be, disorganize and disintegrate a major one. On the Battle Zone the Army Commander was to oppose the enemy's advance with all the forces at his disposal. The Forward Zone comprised a front and intermediate system; the former consisting of outpost line, line of resistance, and counter-attack companies; the latter of a system of isolated forts, wired all round, known as the Line of Redoubts. The Battle Zone likewise consisted of two main lines of defence, organized internally with counter-attack units and wired-in redoubts. The description of these defences may sound formidable till it is explained that there was but one battalion for the defence of each of them to two thousand yards on the front of the 36th Division, and even less density further south. There were likewise Rear Zone defences, notably behind the Canal de St. Quentin and Canal de la Somme. Here it may be added that confusion has been caused in the minds of many by the fashion in which the names "Somme River," "Somme Canal," "St. Quentin Canal," and "Crozat Canal" have been used by various writers in their descriptions of the battle; because the canalized Somme, giving birth to different canals at different parts of its course, was also the main obstacle in two successive lines of defence. The Somme runs south-west from St. Quentin to St. Simon, west for nine miles to Voyennes, then more or less due north to Peronne. Over the first of these three sections it is canalized under the name of the Canal de St. Quentin; over the second two, under that of the Canal de la Somme. Where confusion is apt to arise is in the fact that at St. Simon the Canal de St. Quentin leaves its parent river and runs down to the Oise at Terguier. In the account that follows, the river, a winding, branching stream, will be disregarded, and the Canals, which formed the real obstacles, alluded to always as the Canal de St. Quentin and Canal de la Somme.[50]