In the winter of 1916, General Sir Herbert Plumer, began making plans for a major offensive at Messines. His main objective was to take the Messines Ridge, a strategic position just south-east of Ypres, that had been held by the German Army since December, 1914.
In January 1917, Plumer gave orders for 20 mines to be placed under German lines at Messines. Over the next five months more than 8,000 metres of tunnel were dug and 600 tons of explosive were placed in position.
Employing 2,300 guns and 300 heavy mortars, Plumer began a massive bombardment of German lines on 21st May. Simultaneous explosion of the mines took place at 3.10 on 7th June. The blast killed an estimated 10,000 soldiers and was so loud it was heard in London.
Under a creeping barrage, Plumer sent forward nine divisions of the British Second Army and they took all their preliminary objectives in the first three hours of the battle. Sir Hubert Gough and the British Fifth Army also took advantage of the situation to make significant territorial gains from the Germans. The German Army counter-attacked but by 14th June, the Messines Ridge had been completely occupied by British forces.
The battle for Messines Ridge was the first on the Western Front since 1914 in which defensive casualties (25,000) exceeded attacking losses (17,000).
The battle itself was rehearsed bit by bit. The infantrymen who followed the equally well trained artillerymen's barrage this morning had been drilled for their journey by practice trips far from the scene that left nothing to chance. They had a wonderful model of the ridge - covering more than an acre of ground and true in every detail of contour and adornment - which could be studied for hours. I came back from witnessing the attack early this morning.
For months we had been tunnelling under their lines and had put immense stacks of high explosives into their hillsides. I remember standing all night on a hill near by waiting for those mines to go up just before dawn. It was a quiet night while masses of our men were hidden in the folds of the earth for the big attack, and for miles back our batteries were ready to protect them by tremendous barrage fire.
Just before dawn I heard cocks crowing in villages behind the lines. A glimmer stole through the darkness. A faint imperceptible light crept into the sky. It was 4.30 a.m. Suddenly the earth quaked. A roaring noise rose up from it with tall pillars of earth and flame. Men who had been standing up fell flat. The earth tremor lasted for many seconds. Eleven mines had gone up under the German trenches and fortified positions. Enormous craters gaped open and in them were buried many German soldiers. It was infernal, as though hell had been opened up. Then our batteries began their drum fire and under cover of it our men moved forward. The living enemy was stupefied and stunned.
How many mines went up at once I do not exactly know, but it was nearly a score. Many of these mines were made over a year ago, and since then had lain under German feet undiscovered. In all, I believe over 600 tons of high explosives were fired simultaneously. Can you imagine what over 600 tons of explosives in 20 or so blasts along an arc of 10 miles looks like? I cannot describe it for you. Personally, I can only vouch for having seen nine of the great leaping streams of orange flame which shot upwards from that part of the front immediately before me, each one of the nine a huge volcano in itself, with as many volcanoes going off at the same moment beyond them, hidden by their flames and out of sight, and each vast sheet of flame as it leaped roaring upwards threw up dense masses of dust and smoke, which stood like great pillars towering into the sky, all illuminated by the fires below.
I have seen several of the heaviest bombardments ever conceived by scientific imagination; none of them approached this in volume or variety or terror, and one moment in it will live for ever in the mind of all who were within range as a spectacular miracle of the world. An hour before dawn, as we stood over the dim valley, where the black tree-tops looked like rocks in a calm sea, we saw what might have been doors thrown open in front of a number of colossal blast furnaces. They appeared in pairs, in threes, and in successive singles. With each blast the earth shook and shivered beneath our feet.