The attack was divided up into three main objectives, known as: First objective, the Black line; second objective, the Blue line; third objective, the Brown line; while there was a further objective towards which his attempts, if successful, were to be exploited, known as the Green line.
Before reaching the Black line in all parts of the front, three lines, and in some places four lines, of hostile trenches had to be overcome, as well as numerous communication trenches which contained dug-outs.
Between the Black line and the Blue line, as far as the 152nd Brigade was concerned, lay only two lines of trenches, of which one was in close support to the other. In front of the 154th Brigade the country between the Black and Blue lines was intersected by numerous communication trenches, which led into a central redoubt. In addition, a heavily-wired fire trench traversing the whole brigade front passed through this redoubt.
In consequence, on the left there was little chance of a straightforward attack behind the barrage being completely successful, as it could not be accurately foreshadowed where, in the maze of trenches, resistance was most likely to be met.
[Map IV].—Capture of Vimy Ridge, 9th April 1917.
Between the Blue line and the Black line there were no organised defences, except the communication trenches and a few sections of fire trench connecting one communication trench with another.
The Brown line itself consisted on the left of two heavily-wired fire trenches containing numerous dug-outs. On the right, however, the work had not been completed, and consisted of a section of unfinished fire trench, with a deep sunken road running behind and parallel to it.
On the whole Divisional front the advance to the Blue line lay over a considerable forward slope; beyond the Blue line it continued over a large plateau, finally dropping down on to the Brown line on the reverse slope beyond the plateau.
Prior to the attack a considerable amount of gas was employed against the enemy. Livens projectors, a form of smoke which discharged a cylinder of gas a considerable distance, were chiefly employed. On one occasion on the Divisional front, Mr Livens, the inventor of these projectors, observed their effect from an aeroplane.