The line which the Allies had been holding to the N. of Armentieres since the spring of 1915 formed in plan an inverted letter " S," the lower loop turned to the W., the upper loop turned to the E. and creating the Ypres salient. The lower loop on the other hand represented a pronounced enemy salient jutting into the territory in occupation of the Allies and causing them great inconvenience. Its area consisted almost entirely of high ground which had come to be known as the Messines- Wytschaete ridge. From this dominating position the Germans effectively enfiladed, and to some extent took in reverse, the Allies' trenches to the S. and to the N. of the salient and also commanded the communications leading up to these from the rear, while they overlooked the town of Ypres from within easy field-gun range. Quite apart from any projects for an offen- sive on a great scale, the filling in of this enemy salient -the wresting of the Messines-Wytschaete ridge out of hostile hands was bound to ameliorate the situation in Flanders from the point of view of the Entente and to render the task of barring the invader's way toward the Channel ports so much the easier. In framing his plans for the Flanders offensive Sir. D. Haig had already decided to make the high ground about Messines and Wytschaete his first objective months before the date when the attack upon the position, formidable by nature and rendered infinitely more formidable by the labour that had been expended upon it, actually took place.
General Plumer and his II. Army, who had been acting as the wardens of the Ypres front for more than two years, had been selected to carry this operation out. To enable the II. Army to bring its full force to bear, the V. Army under General Gough had been transferred from the positions which it had been occupying between the III. and IV. Armies in Artois during 1916, to the Ypres salient and it was thus on the left of the II. Preparations for the undertaking had been afoot since the pre- vious summer but they had only been carried on in earnest dur- ing the preceding winter. Moreover all the necessary labour and material had not been available until the prior demands of the Arras scheme of offensive operations had been satisfied, and very strenuous work had consequently to be carried on up to the last moment so as to insure that all would be ready. The preparations included an elaborate railway scheme. Much road construction was an indispensable part of the plan. Special provision for securing an ample water supply had been made. A great force of artillery had been quietly assembled. But the most noteworthy item of all, owing to its virtual novelty, was the carrying into effect of arrangements for a deep mining offensive on a colossal scale. Twenty great mines had been established at the end of galleries running right under the enemy's front line of defence, but one of them had been blown up by the Germans; a total length of 8,000 yards of gallery had, in spite of very active countermining on the part of the enemy, been driven by the tunnelling companies of miners since Jan., and 600 tons of explosives had been distributed between the 19 mines that were effective. The simultaneous explosion of these mines at the moment when the assault was launched was the most remarkable feature in a battle, the exceptionally decisive issue of which was primarily to be attributed to the labour that had been expended in advance, and to the care and forethought of commander and staff which had preceded the opening of the combat. It should be mentioned that the preparations above ground had been carried out under special difficulties owing to most of this area being overlooked from the German lines.
For the defence of this salient which they occupied, and the importance of which they fully realized, the Germans depended upon two separate sets of lines, coinciding in trace with its arc. The more advanced set of lines of the two was close to the trenches that were occupied by General Plumer's troops, and it was at most points pushed down the forward slope of the high ground. The second set of lines on the other hand, which formed an inner curve, followed the crest of the Messines-Wytschaete ridge along most of its extent. The villages of Messines and Wytschaete had been organized as main centres of resistance capable of offering a stout defence, and many farms, hamlets
and copses existing along the line had been utilized to form defensive posts. The Germans had moreover also constructed two chord positions stretching along the base of the salient partly on and partly below the reverse slopes of the high ground. The front one of these two positions represented the final objec- tive given to the assaulting columns by General Plumer.
The troops of the II. Army detailed for the enterprise con- sisted, enumerating them from right to left, of the II. Anzac Corps under Lt.-Gen. Sir A. Godley (Australian 3rd Div., ISJew Zealand Div., 25th Div.), with the Australian 4th Div. in support; the IX. Corps under Lt.-Gen. Hamilton-Gordon (36th Div., i6th Div., igth Div.), with the nth Div. in support; and the X. Corps under Lt.-Gen. Sir T. Morland (41 st Div., 47th Div., 23rd Div.), with the 24th Div. in support. There were thus nine divisions in front line and three in support. As the final objective of the troops along the whole battle-front was the chord of the arc forming the salient, it followed that the divisions in the centre would have a greater distance to cover than the divisions on the flanks; this had been taken into account and had been provided for in the time-table. The moment of assault was fixed for 3:10 A.M. on the morning of June 7, and at that hour the 19 mines were exploded beneath the enemy's front line with devastating effect. At a number of points the hostile trenches were completely obliterated and their garrisons wiped out, so that when the assailants reached the enemy's front line under cover of a tremendous bombardment, very little resistance was offered and the first objective was secured almost at once. The consequence was that, as had been anticipated in the programme, the advancing infantry could proceed without delay to the execution of their next task, that of carrying the second German line. The capture of this proved more difficult than had that of the front defences. In some of the skilfully prepared localities the enemy detachments would not yield for some time, in spite of the storm of shell pouring down upon them; but such localities speedily became isolated as the assail- ants pushed on between them, and their fall was not then long delayed. The strongly fortified village of Messines was, accord- ing to the programme, taken by the New Zcalanders. Wytschaete was captured after a determined struggle by portions of the 36th (Ulster) and of the i6th (Irish) Divs. fighting side by side. On the left, where a trough which is followed by the Ypres-Comines canal cuts through the belt of high ground, the 47th (London) Div. had very formidable obstacles to overcome but pressed steadily forward and took many prisoners. The movements of the attacking side had been somewhat hampered at the outset by the dim light and by the air being dust-laden owing to the great explosions; but as the morning wore on this impediment to advance disappeared. An interesting feature in the opening phase of the battle had been that the tanks told off to assist the advancing battalions had in many cases been unable to get up in time to share in the struggles for the German second line of defence, so rapid had been the movements of the infantry. The operations had proceeded in almost exact accordance with the time-table, and by early in the forenoon all the upper part of the Messines-Wytschaete ridge and of its extension north- eastward to the limit of the battlefield was in the hands of British and Australasian troops. These moreover had consoli- dated the ground that they had won, and they were holding a line which, along most of its extent, was on the reverse slope of the high ground and overlooked the German chord lines of trenches; guns had also been pushed forward promptly to assist at closer range the advance which was to be made against these as the final operations of the day.
This closing effort took place in the afternoon and it was completely successful, although the enemy showed some dis- position to counter-attack and at some points offered a stubborn resistance. So it came about that by the evening the last objec- tive had been fully attained, and that General Plumer and his army had placed an extraordinarily complete and decisive tactical success to their credit. The extent of the success was not to be measured merely by the importance and extent of the area of ground which had been wrested out of the enemy's
