The lowland west of the ridge was a mixture of meadows and fields, with high hedgerows dotted with trees, cut by streams and a network of drainage ditches emptying into canals.

[17] Sappers dug the tunnels into a layer of blue clay 80–120 ft (24–37 m) underground, then drifted galleries for 5,964 yd (3.389 mi; 5.453 km) to points deep underneath the front position of Gruppe Wijtschate, despite German counter-mining.

[20] Co-ordinated by tunnelling companies of the Royal Engineers, Canadian, Australian, New Zealand and British miners laid 26 mines with 447 long tons (454 t) of ammonal explosive.

[30] Large numbers of posts for machine-guns to fire an overhead barrage were built and protective pits were dug for mules, each of which was to carry 2,000 rounds of ammunition to advanced troops.

Three field companies of engineers with a pioneer battalion were kept in reserve, to follow up the attacking infantry, rebuild roads and work on defensive positions as ground was consolidated.

The divisional trench mortar batteries were to bombard the German front line opposite the 142nd Brigade, where it was too close for the artillery to shell without endangering British troops.

The first section began 6 mi (9.7 km) behind Messines Ridge, running north from the Lys to Linselles then Werviq and Beselare, where the nearest areas giving good artillery observation to the west were found.

In April, Field Marshal Crown Prince Rupprecht and his chief of staff, Generalleutnant (Lieutenant-General) Hermann von Kuhl, favoured withdrawal to the Warneton (third) line, before a British attack.

If they had to fall back, the support battalions would advance to restore the front system, except at Spanbroekmolen Hill, which due to its importance was to be held at all costs (unbedingtes Halten).

[63] British air observation on the reverse slope was less effective than in the foreground but the villages of Mesen and Wijtschate were demolished, as were much of the Höhenstellung and Sehnenstellung, although many pill boxes survived.

Long-range fire on Comines, Warneton, Wervicq and villages, road junctions, railways and bridges caused much damage and a number of ammunition dumps were destroyed.

There was a thunderstorm in the evening of 6 June but by midnight the sky had cleared and at 2:00 a.m., British aircraft cruised over the German lines to camouflage the sound of tanks as they drove to their starting points.

The 3rd Australian Division on the right, had been disorganised by a German gas bombardment on Ploegsteert (Plugstreet to the British) Wood around midnight, which caused 500 casualties during the approach march but the attack between St Yves and the river Douve began on time.

The two attacking brigades crossed the dry riverbed of the Steenebeke and took the German front line, despite the mine at La Petite Douve Farm not being fired and then advanced towards Messines village.

Two machine-gun posts on the edge of the village were rushed but fire from Swayne's Farm 400 yd (370 m) north held up the advance, until a tank drove through it and caused 30 German troops to surrender.

[73] In the IX Corps area, the 36th (Ulster) Division captured the wreckage of two woods and Bogaert Farm in between, finding that the artillery fire had cut the masses of barbed wire and destroyed many strongpoints.

White Château was attacked by the 47th Division as it advanced to the first objective, covered by smoke and Thermite shells fired on the German positions further to the north, along the Comines Canal.

At 9:00 a.m. the infantry withdrew to allow the area to be bombarded from 2:30 to 6:55 p.m. for an attack by a reserve battalion at 7:00 p.m.[81] The 23rd Division had many casualties caused by flanking machine-gun fire from the spoil heap while clearing Battle Wood, which took until the evening.

[82] In the centre of the attack, a company from each battalion advanced behind the barrage, to an observation line several hundred yards down the east slope of the ridge, at 8:40 a.m. assisted by eight tanks and patrols of cavalry.

The brigades captured 289 Germans and six field guns for a loss of six casualties, advancing 800 yd (730 m) along the Roozebeek valley, then took Ravine Wood unopposed on the left flank.

An SOS barrage on the IX Corps front stopped a German counter-attack from the Roozebeke valley but many shells fell short, precipitating another informal withdrawal.

Some troops, poorly trained and inexperienced, failed to co-operate, fearing exposure to the Germans; aircraft flew dangerously low to identify them, four being shot down in consequence.

[97][j] Some of the Stoßtruppen (Stormtroops) in breastwork Ic were able to counter-attack but were overwhelmed quickly as the British advanced on the Sonnestellung (Sun Position), which usually held half of the support battalions but had been reduced to about 100 men and six machine-guns, in each 800 yd (730 m) regimental zone.

[99] Smoke and dust from the British barrage limited visibility to 100 yd (91 m) and some defenders thought that the figures moving towards them were retreating German soldiers, were taken by surprise and overrun.

[104] In 1930, Basil Liddell Hart thought the success at Messines inflated expectations for the Third Battle of Ypres and that because the circumstances of the operations were different, attempts to apply similar tactics resulted in failure.

[111] Ian Brown in his 1996 PhD thesis and Andy Simpson in 2001 concluded that extending British supply routes over the ridge, which had been devastated by the mines and millions of shells, to consolidate the Oosttaverne line was necessary.

In volume XII of Der Weltkrieg the German Official Historians recorded 25,000 casualties for the period 21 May – 10 June including 10,000 missing of whom 7,200 were reported as taken prisoner by the British.

The mistaken bombardments of friendly troops ended late on 9 June, when the New Zealand, 16th (Irish) and 36th (Ulster) divisions were withdrawn into reserve and the normal corps organisation was restored; the anticipated large German counter-attacks had not occurred.

[121] The 3rd Australian Division advanced 600 yd (550 m) either side of the river Douve, consolidating their hold on a rise around Thatched Cottage, which secured the right flank of the new Messines position; early on 11 June, the Germans evacuated the Blauwepoortbeek sector.

On 14 June, the II Anzac Corps was to push forward on the right from Plugstreet Wood to Trois Tilleuls Farm and Hill 20 and another 1,000 yd (910 m) to the Gapaard spur and Ferme de la Croix.