Mines in the Battle of Messines (1917)

The Mines in the Battle of Messines comprised a series of mines built near the village of Messines in Belgian West Flanders during the First World War. At the start of the Battle of Messines (7–14 June 1917), a series of mines was detonated beneath German lines, creating 19 large craters. The joint explosion of the mines in the Battle of Messines ranks among the largest non-nuclear explosions of all time. The evening before the attack, General Sir Charles Harington remarked to the press, "Gentlemen, we may not make history tomorrow, but we shall certainly change the geography."

Background
As part of the allied operations in the Ypres Salient, the British had begun a mining offensive against the German-held Wijtschate (sic) salient in 1916. Sub-surface conditions were especially complex and separate ground water tables made mining difficult. To overcome the technical difficulties, two military geologists assisted the miners from March 1916, including Edgeworth David, who planned the system of mines.

Co-ordinated by tunnelling companies of the Royal Engineers, Canadian, Australian, New Zealand and British miners dug a line of mines charged with a total of 447 LT of ammonal explosive. Sappers dug the tunnels into a layer of "blue clay" 80 – below the surface, then drifted galleries (horizontal passages in underground mines) for 5964 yd to points beneath the position of Gruppe Wytschaete, despite German counter-mining. German tunnellers often came within metres of several British mine chambers. Before the Battle of Messines, German counter-mining troops found the Petit Douve Farm mine and wrecked the chamber with a camouflet. The British diverted the attention of German miners from their deepest galleries, by making many secondary attacks in the upper levels.

In preparation of the Battle of Messines, two mines were laid at Hill 60 on the northern flank, one at St Eloi, three at Hollandscheschur Farm, two at Petit Bois, single mines at Maedelstede Farm, Peckham House and Spanbroekmolen, four at Kruisstraat, one at Ontario Farm and two each at Trenches 127 and 122 on the southern flank. The largest single mines were at St Eloi, which was charged with 95600 lb of ammonal, at Maedelstede Farm, which was charged with 94000 lb, and beneath German lines at Spanbroekmolen, which was charged with 91000 lb of ammonal. The Spanbroekmolen mine was set 88 ft below ground, at the end of a gallery 1710 ft long. When detonated on 7 June 1917, the blast formed the "Lone Tree Crater" with a diameter of 250 ft and a depth of 40 ft. By contrast, the mine at Ontario Farm did not produce a crater but only left a shallow indentation in the soft clay. Six more mines were prepared, but not fired in the event: four on the extreme southern flank (Birdcage 1–4) were not required because the ridge fell so quickly, Peckham 2 was abandoned due to a tunnel collapse, and the mine at Petit Douve Farm (see above) was lost to a German counter-mining attack.