Editing Battle of Passchendaele (section)

===Battle of Messines===<!-- This section is linked from 7 June -->

{{main|Battle of Messines (1917)}}

[[File:NLS Haig - Smashed up German trench on Messines Ridge with dead (cropped).jpg|thumb|{{centre|German trench destroyed by a mine explosion}}]]
The first stage in the British plan was a preparatory attack on the German positions south of Ypres at Messines Ridge. The Germans on the ridge had observation over Ypres and unless it was captured, observed [[enfilade]] artillery-fire could be fired against a British attack from the salient further north.{{sfn|Sheldon|2007|p=1}} Since mid-1915, the British had been [[Mining (military)|mining]] under the German positions on the ridge and by June 1917, [[Mines in the Battle of Messines (1917)|21 mines]] had been filled with nearly {{cvt|1000000|lb|t|0}} of explosives.{{sfn|Hart|Steel|2001|pp=41–44}} The Germans knew the British were mining and had taken counter-measures but they were surprised at the extent of the British effort.{{sfn|Sheldon|2007|p=23}} Two of the mines failed to detonate but {{nowrap|19 went}} off on 7 June, at {{nowrap|3:10&nbsp;a.m.}} [[British Summer Time]]. The final objectives were largely gained before dark and the British had fewer losses than the expected {{nowrap|50 per cent in}} the initial attack. As the infantry advanced over the far edge of the ridge, German artillery and machine-guns east of the ridge opened fire and the British artillery was less able to suppress them.{{sfn|Hart|Steel|2001|p=55}} The attack removed the Germans from the dominating ground on the southern face of the Ypres salient, which the 4th Army had held since the First Battle of Ypres in 1914.{{sfn|Edmonds|1991|p=87}}