British preparations The Second Army centralised its artillery and devised a plan of great sophistication, following the precedent set at the
Battle of Arras in April. The use of field survey, gun
calibration, weather data and a new and highly accurate map, much improved artillery accuracy. Systematic target-finding was established by the use of new sound-ranging equipment, better organisation of flash-spotting and the communication of results through the Army Report Centre at Locre Château.
Counter-battery artillery bombardments increased from twelve in the week ending 19 April, to in the last ten days before the attack. A survey of captured ground after the battle found that of the German artillery positions had been plotted. The 2nd Field Survey Company also assisted mining companies by establishing the positions of objectives within the German lines, using
intersection and a special series of aerial photographs. The company surveyed advanced artillery positions for guns to be moved forward to them and open fire as soon as they arrived. The British had begun a mining offensive against the (Wytschaete position) in 1916. Sub-surface conditions were especially complex and separate ground water tables made mining difficult. Two military geologists assisted the miners from March 1916, including
Edgeworth David, who planned the system of mines. Sappers dug the tunnels into a layer of
blue clay underground, then drifted galleries for to points deep underneath the front position of , despite German counter-mining. German tunnellers came close to several British mine chambers, found the mine at La Petite Douve Farm and wrecked the chamber with a . The British diverted the attention of German miners from their deepest galleries by making many secondary attacks in the upper levels. Co-ordinated by
tunnelling companies of the Royal Engineers, Canadian, Australian, New Zealand and British miners laid with of
ammonal explosive. Two mines were laid at on the northern flank, one at
St Eloi, three at Hollandscheschuur, two at Petit Bois, one each at Maedelstede Farm, Peckham House and Spanbroekmolen, four at Kruisstraat, one at Ontario Farm and two each at trenches on the southern flank. One of the largest of the mines was at Spanbroekmolen; Lone Tree Crater formed by the blast of of ammonal in a chamber at the end of a gallery long, below ground was in diameter and deep. The British knew of the importance the Germans placed on holding the salient, after a captured corps order from stating "that the salient be held at all costs" was received by Haig on 1 June. In the week before the attack, and
howitzers bombarded the German trenches, cut wire, destroyed strongpoints and conducted
counter-battery fire against German artillery pieces, using The 4th Army artillery consisted of fifty-four twenty-four guns, and four heavy and guns. In May, the
4th Australian Division,
11th (Northern) Division and the
24th Division were transferred from Arras as reserve divisions for the Second Army corps in the attack on Messines Ridge. Seventy-two of the new
Mark IV tanks also arrived in May and were hidden south-west of Ypres. British aircraft began to move north from the Arras front, the total rising to about aircraft in the II Brigade RFC (Second Army) area. The mass of artillery to be used in the attack was supported by many artillery-observation and photographic reconnaissance aircraft, in the corps squadrons which had been increased from twelve to eighteen aircraft each. Strict enforcement of wireless procedure allowed a reduction of the minimum distance between observation aircraft from at Arras in April to at Messines, without mutual wireless interference. Wire-cutting bombardments began on 21 May and two days were added to the bombardment for more counter-battery fire. The main bombardment began on 31 May, with only one day of poor weather before the attack. Two flights of each observation squadron concentrated on counter-battery observation and one became a bombardment flight, working with particular artillery bombardment groups for wire cutting and trench-destruction; these flights were to become contact-patrols to observe the positions of British troops once the assault began. The attack barrage was rehearsed on 3 June to allow British air observers to plot masked German batteries, which mainly remained hidden but many minor flaws in the British barrage were reported. A repeat performance on 5 June, induced a larger number of hidden German batteries to reveal themselves. The
25th Division made its preparations on a front from the Wulverghem–Messines road to the Wulverghem–Wytschaete road, facing of the German front line, which tapered to the final objective, wide, at the near crest of the ridge, distant, behind nine German defensive lines. The advance would begin up a short rise to the near edge of the Steenbeek Valley, then up the steep rise from the valley floor between Hell and Sloping Roof farms to Four Huns, Chest and Middle farms on the main ridge, with Lumm Farm on the left flank of the objective. Artillery emplacements for the 25th divisional artillery and 112th Army Field Brigade were built and the Guards Division field artillery was placed in concealed forward positions. Road making and the construction of dugouts and communication trenches took place first between 12 and 30 April and then between 11 May and 6 June. In three hours, an assembly trench was dug from the German front line on the night of complete with communication trenches and barbed wire. Bridges and ladders were delivered in the two days before the attack. of telephone cable was dug in at least deep, which withstood fifty German artillery hits before the British attack. 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 rounds of ammunition to advanced troops. (Machine-guns were fired like artillery, over the heads of the advancing infantry. The bullets of an overhead barrage came down ahead of the attacking troops on German-held areas, forcing the garrison under cover.) 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 artillery devised a creeping and standing barrage plan and time-table, tailored to the estimated rates of advance of the infantry. The standing barrage lifts were to keep all trenches within of the infantry under continuous fire. The
howitzer,
howitzer and
howitzers involved, were to change targets only when infantry got within . The
18-pounder field gun standing barrages would then jump over the creeping barrages to the next series of objectives. The concealed guns of the Guards Division field artillery were to join the creeping barrage for the advance at and at the 112th Army Field Brigade was to advance to the old front line, to be ready for an anticipated German counter-attack by The
47th (1/2nd London) Division planned to attack with two brigades, each reinforced by a battalion from the reserve brigade, along either side of the Ypres–Comines Canal. Large numbers of machine-guns were organised to fire offensive and defensive barrages and signal detachments were organised to advance with the infantry. An observation balloon was reserved for messages by signal lamp from the front line, as insurance against the failure of telephone lines and message-runners. 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. Wire-cutting began in mid-May, against considerable local retaliation by German artillery. At the end of May the two attacking brigades went to Steenvoorde to train on practice courses built to resemble the German positions, using air reconnaissance photographs to mark the positions of machine-gun posts and hidden barbed wire. Divisional intelligence summaries were used to plan the capture of German company and battalion headquarters. The 140th Brigade, with four tanks attached, was to occupy White Château and the adjacent part of , while the 142nd Brigade attacked the spoil heaps and the canal bank to the left. On 1 June, the British artillery began the intense stage of the preparatory bombardment for trench-destruction and wire cutting; the two attacking brigades assembled for the attack from 4 to 6 June. British fighter aircraft tried to prevent German artillery-observation aircraft from operating by dominating the air from the British front line to the German balloon line, about beyond. Better aircraft like the
Bristol Fighter,
S.E.5a and the
Royal Naval Air Service (RNAS)
Sopwith Triplane had entered service since Arras and matched the performance of German
Albatros D.III and
Halberstadt D.II fighters. For the week before the attack, the barrage line was patrolled all day by fighters at with more aircraft at in the centre of the attack front. No British corps aircraft were shot down by German aircraft until 7 June, when aircraft were able to direct artillery fire simultaneously over the three attacking corps. Behind the barrage line lay a second line of defence, which used wireless interception to take bearings on German artillery-observation aircraft to guide British aircraft into areas where German flights were most frequent. By June 1917, each British army had a control post of two aeroplane compass stations and an aeroplane intercepting station, linked by telephone to the army wing headquarters, fighter squadrons, the anti-aircraft commander and the corps heavy artillery headquarters. The new anti-aircraft communication links allowed areas threatened by German bombardment to be warned, German artillery spotting aircraft to be attacked and German artillery batteries to be fired on when they revealed themselves. From 1 to 7 June, the II Brigade RFC had from wireless interception, shot down one German aircraft, damaged seven and stopped artillery bombardments. Normal offensive patrols continued beyond the barrage line out to a line from Ypres to Roulers and Menin, where large formations of British and German aircraft clashed in long
dogfights, once German air reinforcements began operating in the area. Longer-range bombing and reconnaissance flights concentrated on German-occupied airfields and railway stations and the night bombing specialists of
100 Squadron attacked trains around Lille, Courtrai, Roulers and Comines. Two squadrons were reserved for close air support on the battlefield and low attacks on German airfields.
Plan Objective lines The British planned to advance on a front from St Yves to Mt Sorrel, eastwards to the Oosttaverne line, a maximum depth of . Three intermediate objectives, originally to be reached a day at a time, became halts, where fresh infantry would
leap-frog through to gain the ridge in one day. In the afternoon a further advance down the ridge was to be made. The attack was to be conducted by three corps of the Second Army (General Sir Herbert Plumer).
II Anzac Corps in the south-east was to advance ,
IX Corps in the centre was to attack on a front, which would taper to at the summit and
X Corps in the north had an attack front wide. The corps planned their attacks under the supervision of the army commander, using analyses of the Somme operations of 1916 and successful features of the attack at Arras on 9 April as guides. Great care was taken in the planning of counter-battery fire, the artillery barrage time-table and machine-gun barrages.
Artillery German artillery positions and the second () (Contour Position) position were not visible to British ground observers. For observation over the rear slopes of the ridge, were concentrated in II Brigade RFC and eight balloons of II Kite Balloon Wing were placed behind the British front line. The Second Army artillery commander, Major-General George Franks, co-ordinated the corps artillery plans, particularly the heavy artillery arrangements to suppress German artillery, which were devised by the corps and divisional artillery commanders. The Second Army Report Centre at Locre Château was linked by buried cable to each corps report centre, corps heavy artillery headquarters, divisional artillery headquarters, RFC squadrons, balloon headquarters, survey stations and wireless stations. Responsibility for counter-battery fire was given to a counter-battery staff officer with a small staff, who concentrated exclusively on the defeat of the German artillery. A conference was held each evening by the counter-battery staffs of divisions and corps, methodically to collate the day's reports from observation aircraft and balloons, field survey companies, sound ranging sections and forward observation officers. Each corps had a counter-battery area, which was divided into zones and allotted to heavy artillery groups. Each heavy artillery group headquarters divided their zones into map squares, which were allotted to artillery batteries, to be ready swiftly to open fire on them. The attacking corps organised their heavy artillery within the army plan according to local conditions. II Anzac Corps created four counter-battery groups, each with one heavy artillery group and IX Corps arranged four similar groups and five bombardment groups, one for each of its three divisions and two (with the heaviest howitzers) in reserve, under the control of the corps heavy artillery commander. A Heavy Artillery Group Commander was attached to each divisional artillery headquarters, to command the heavy artillery once the infantry attack began. Field artillery arrangements within corps also varied, in IX Corps groups and sub-groups were formed so that infantry brigades had an artillery liaison officer and two sub-groups, one with six batteries and one with six batteries. Surplus field artillery brigade headquarters planned forward moves for the guns and were kept ready to replace casualties. It was expected that much of the artillery would need to switch rapidly from the bombardment plan to engage counter-attacking German infantry. It was planned that the
Forward Observation Officers of the divisions in the first attack onto the ridge would control the artillery which had remained in place and the reserve divisions advancing down the far slope to the Oosttaverne line would control the artillery hidden close to the front line and the artillery which advanced into no-man's-land. Franks planned to neutralise German guns within of the attack front. On the flanks of the British attack front of , guns had been located, for which guns ( the German total) were set aside. The guns in the path of the attack were each to be engaged by a British gun, a formula which required guns and howitzers to be reserved for counter-battery fire. Every of front had a medium or heavy howitzer for bombardment, which required , with guns and howitzers (five per cent) deployed with the field artillery that was due to fire the creeping and standing barrages. Franks devised a bombardment timetable and added arrangements for a massed machine-gun barrage. The and heavy guns and howitzers were organised in forty groups and the guns and howitzers in sixty-four field artillery brigades within the attacking divisions and thirty-three Army field artillery brigades, divided among the three attacking corps; of ammunition was delivered, for each , per howitzer, for each medium and heavy piece and another and shells for the field guns. Two-thirds of the were to fire a
creeping barrage of
shrapnel immediately ahead of the advance, while the remainder of the
field guns and howitzers were to fire a standing barrage, further ahead on German positions, lifting to the next target when the infantry came within of the barrage. Each division was given four extra batteries of field artillery, which could be withdrawn from the barrage at the divisional commander's discretion to engage local targets. The field batteries of the three reserve divisions were placed in camouflaged positions close to the British front line. As each objective was taken by the infantry, the creeping barrage was to pause ahead and become a standing barrage while the infantry consolidated. During this time the pace of fire was to slacken to one round per-gun per-minute, allowing the gun-crews a respite, before resuming full intensity as the barrage moved on. The heavy and super-heavy artillery was to fire on German artillery positions and rear areas and were to fire a barrage over the heads of the advancing troops.
Mines At the mines were to be detonated, followed by the attack of nine divisions onto the ridge. The blue line (first objective) was to be occupied by followed by a two-hour pause. At the advance to the black line (second objective) would begin and consolidation was to start by Fresh troops from the unengaged brigades of the attacking divisions or from the reserve divisions would then pass through, to attack the Oosttaverne line at As soon as the black line was captured, all guns were to bombard the Oosttaverne line, conduct counter-battery fire and place a standing barrage beyond the black line. All operational tanks were to join with the in reserve, to support the infantry advance to the Oosttaverne line.
German preparations The Messines defences were on a forward slope and could be overlooked from Haubourdin Hill , the south end of the Douve Valley and Kemmel Hill, west of , an arrangement which the experience of 1916 showed to be obsolete. A new line, incorporating the revised principles of defence derived from the experience of the Battle of the Somme, known as the , began in February 1917. The first section began 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, (Lieutenant-General)
Hermann von Kuhl, favoured withdrawal to the Warneton (third) line, before a British attack. The local divisional commanders objected, due to their belief that counter-mining had neutralised the British underground threat and the inadequacy of the Warneton line. The convex eastern slope limited artillery observation and the canal and the river Lys restricted the space below the ridge where infantry could manoeuvre for counter-attacks. British observation from the ridge would make the ground to the east untenable as far as the beyond. A withdrawal to the would endanger the southern slopes of Menin Ridge, the most important area of the . Rupprecht re-examined the Warneton (third) line and the extra between the Warneton Line and the (Contour Position) and dropped the withdrawal proposal. of the 4th Army, with three divisions under the command of the headquarters of
XIX Corps (General
Maximilian von Laffert), held the ridge and was reinforced with the 24th Division in early May. The 35th and 3rd Bavarian divisions were brought up as divisions and was substantially reinforced with artillery, ammunition and aircraft. The vulnerability of the northern end of Messines Ridge, where it met the Menin Ridge, led to the German command limiting the frontage of the 204th () Division to . The 24th Division to the south held and the 2nd Division at held . In the south-east, of the front line either side of the river Douve, was defended by the
40th Division. The front-line was lightly held, with fortifications distributed up to behind the front line. At the end of May, British artillery fire was so damaging that the 24th and 40th divisions were relieved by the 35th and 3rd Bavarian () divisions, which were replaced by the
7th and
1st Guard Reserve divisions in early June; relief of the 2nd Division was promised for June. The German front line regiments held areas wide with one () battalion forward, one () battalion in support and the third in reserve back. The battalion usually had three companies in the front system (which had three lines of
breastworks called "Ia", "Ib" and "Ic") and one in the (intermediate) line (with a company of the support battalion, available for immediate counter-attack) between the front system and the on the ridge crest. The other three companies of the support battalion sheltered in the . About posts per regimental sector were dispersed around the defensive zone. The German defence was intended to be mobile and in "Ic" the third breastwork had to conduct immediate counter-attacks to recapture "Ia" and "Ib". 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 (). On 8 May, the British preliminary bombardment began and on 23 May became much heavier. The breastworks of the front defences were demolished and concrete shelters on both sides of the ridge were systematically destroyed. Air superiority allowed the British artillery observation aircraft to cruise over the German defences, despite the efforts of
Jagdgeschwader 1 (the Richthofen Circus). On 26 May, the German front garrisons were ordered to move forward into shell-holes in no-man's-land at dawn and return to their shelters at night. When the shelters were destroyed, shell-hole positions were made permanent, as were those of the companies further back. Troops in the were withdrawn behind the ridge and by the end of May, the front battalions changed every two days instead of every five, due to the effect of the British bombardment. Some German troops on the ridge were convinced of the mine danger and their morale was depressed further by the statement of a prisoner taken on 6 June, that the attack would be synchronised with mine explosions. On 1 June, the British bombardment became more intense and nearly every German defensive position on the forward slope was obliterated. The (German air service) effort reached its maximum on 4 and 5 June, when German aircraft observed counter-battery shoots and wireless interception by the British showed German aircraft, escorted by up to seven fighters each, directing artillery fire against the Second Army. British air observation on the reverse slope was less effective than in the foreground but the villages of and were demolished, as were much of the and , 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. ==Battle==