The Third Battle of Ypres (German: Dritte Flandernschlacht; French: Troisième Bataille des Flandres; Dutch: Derde Slag om Ieper), also known as the Battle of Passchendaele ( PASH-ən-dayl), was a campaign of the First World War, fought by the Allies against the German Empire. The battle took place on the Western Front, from July to November 1917, for control of the ridges south and east of the Belgian city of Ypres in West Flanders, as part of a strategy decided by the Entente at conferences in November 1916 and May 1917. Passchendaele (now Passendale) lies on the last ridge east of Ypres, 5 mi (8 km) from Roulers (now Roeselare), a junction of the Bruges-(Brugge)-to-Kortrijk railway. The station at Roulers was on the main supply route of the German 4th Army. Once Passchendaele Ridge had been captured, the Allied advance was to continue to a line from Thourout (now Torhout) to Couckelaere (Koekelare). Further operations and a British supporting attack along the Belgian coast from Nieuport (Nieuwpoort), combined with an amphibious landing (Operation Hush), were to have reached Bruges and then the Dutch frontier. Although a general withdrawal had seemed inevitable in early October, the Germans were able to avoid one due to the resistance of the 4th Army, unusually wet weather in August, the beginning of the autumn rains in October and the diversion of British and French resources to Italy. The campaign ended in November, when the Canadian Corps captured Passchendaele, apart from local attacks in December and early in the new year. The Battle of the Lys (Fourth Battle of Ypres) and the Fifth Battle of Ypres of 1918, were fought before the Allies occupied the Belgian coast and reached the Dutch frontier. A campaign in Flanders was controversial in 1917 and has remained so. The British Prime Minister, David Lloyd George, opposed the offensive, as did General Ferdinand Foch, the Chief of Staff of the French Army. Field Marshal Sir Douglas Haig, commander of the British Expeditionary Force (BEF) did not receive approval for the Flanders operation from the War Cabinet until 25 July. Matters of dispute by the participants, writers and historians since 1917 include the wisdom of pursuing an offensive strategy in the wake of the Nivelle Offensive, rather than waiting for the arrival of the American Expeditionary Force (AEF) in France. Controversies also debated are the choice of Flanders, its climate, the selection of General Hubert Gough and the Fifth Army to conduct the offensive and debates over the nature of the opening attack and between advocates of shallow and deeper objectives. Also debated are the time between the Battle of Messines (7–14 June) and the first Allied attack (the Battle of Pilckem Ridge, 31 July) the extent to which the French Army mutinies influenced the British, the effect of the exceptional weather, the decision to continue the offensive in October and the human costs of the campaign.
Background
Flanders
1914
Belgium had been recognised in the Treaty of London (1839) as a sovereign and neutral state after the secession of the southern provinces of the Netherlands in 1830. The German invasion of Belgium on 4 August 1914, in violation of Article VII of the treaty, was the British casus belli against Germany. British military operations in Belgium began with the arrival of the British Expeditionary Force (BEF) at Mons on 22 August. Operations in Flanders began during the Race to the Sea, reciprocal attempts by the French and German armies to turn their opponents' northern flank, through Picardy, Artois and Flanders. On 10 October, Lieutenant-General Erich von Falkenhayn, the Chief of Staff of the Oberste Heeresleitung (OHL, supreme army command), ordered an attack towards Dunkirk and Calais, followed by a turn south behind the Allied armies, to gain a decisive victory. On 16 October, the Belgians and some French reinforcements began the defence of western Belgium and the French Channel ports, at the Battle of the Yser. When the German offensive failed, Falkenhayn ordered the capture of Ypres to gain a local advantage. By 18 November, the First Battle of Ypres had also ended in failure, at a cost of 160,000 German casualties. In December, the British Admiralty began discussions with the War Office, for a combined operation to re-occupy the Belgian coast but were obliged to conform to French strategy and participate in offensives further south.
==== 1915 ==== Large British offensive operations in Flanders were not possible in 1915, due to a lack of resources. The Germans conducted their own Flanders offensive at the Second Battle of Ypres (22 April – 15 May 1915), making the Ypres salient more costly to defend. Sir Douglas Haig succeeded Sir John French as Commander-in-Chief of the BEF on 19 December. A week after his appointment, Haig met Rear-Admiral Reginald Bacon, who emphasised the importance of obtaining control of the Belgian coast, to end the threat posed by German U-boats. Haig was sceptical of a coastal operation, believing that a landing from the sea would be far more difficult than anticipated and that an advance along the coast would require so much preparation, that the Germans would have ample warning. Haig preferred an advance from Ypres, to bypass the flooded area around the Yser and the coast, before attempting a coastal attack to clear the coast to the Dutch border.
1916
Minor operations took place in the Ypres salient in 1916, some being German initiatives to distract the Allies from their preparations for the offensive at Verdun and later attempts to divert Allied resources from the Battle of the Somme. Other operations were begun by the British to regain territory or to evict the Germans from ground overlooking their positions. Engagements took place on 12 February at Boesinghe and on 14 February at Hooge and Sanctuary Wood. There were actions from 14 to 15 February and 1 to 4 March at The Bluff, 27 March – 16 April at the St Éloi Craters and the Battle of Mont Sorrel from 2 to 13 June. In January 1917, the Second Army (General Herbert Plumer) with the II Anzac, IX, X and VIII corps, held the Western Front in Flanders from Laventie to Boesinghe, with eleven divisions and up to two in reserve. There was much trench mortaring, mining and raiding by both sides and from January to May, the Second Army suffered 20,000 casualties. In May, reinforcements began arriving in Flanders from the south; the II Corps headquarters and 17 divisions had arrived by the end of the month. In January 1916, Plumer began to plan offensives against Messines Ridge, Lille and Houthulst Forest. General Henry Rawlinson was also ordered to plan an attack from the Ypres Salient on 4 February; planning continued but the Battle of Verdun and the Battle of the Somme took up the rest of the year. In November, Haig, the French commander-in-chief Joseph Joffre and the other Allies met at Chantilly. The commanders agreed on a strategy of simultaneous attacks, to overwhelm the Central Powers on the Western, Eastern and Italian fronts, by the first fortnight of February 1917. A meeting in London of the Admiralty and the General Staff urged that the Flanders operation be undertaken in 1917 and Joffre replied on 8 December, agreeing to a Flanders campaign after the spring offensive. The plan for a year of attrition offensives on the Western Front, with the main effort to be made in the summer by the BEF, was scrapped by the new French Commander-in-Chief Robert Nivelle in favour of a return to a strategy of decisive battle.
Allied strategy
Nivelle planned preliminary offensives to pin German reserves by the British at Arras and the French between the Somme and the Oise, then a French breakthrough offensive on the Aisne, followed by pursuit and exploitation. Haig had reservations and on 6 January Nivelle agreed to a proviso that if the first two parts of the operation failed to lead to a breakthrough, the operations would be stopped and the British could move their forces north for the Flanders offensive, which was of great importance to the British government. On 23 January, Haig wrote that it would take six weeks to move British troops and equipment to Flanders and on 14 March, noted that the Messines Ridge operation could begin in May. On 21 March, he wrote to Nivelle that it would take two months to prepare the offensive from Messines to Steenstraat but that the Messines operation could be ready in five or six weeks. The main French attack took place from 9 April to 9 May and failed to achieve a breakthrough. On 16 May, Haig wrote that he had divided the Flanders operation into two parts, one to take Messines Ridge and the main attack several weeks later. British determination to clear the Belgian coast took on more urgency after the Germans resumed unrestricted submarine warfare on 1 February 1917. On 1 May 1917, Haig wrote that the Nivelle Offensive had weakened the German army but that an attempt at a decisive blow would be premature. The wearing-out process would continue on a front where the Germans had no room to retreat. Even limited success would improve the tactical situation in the Ypres salient, reducing the exceptional wastage, even in quiet periods. In early May, Haig set the date for the Flanders offensive, the attack on Messines Ridge to begin on 7 June.
Kerensky offensive
The Russian army conducted the Kerensky Offensive in Galicia, to honour the agreement struck with the Allies at the Chantilly meeting of 15 to 16 November 1916. After a brief period of success from 1 to 19 July, the Russian offensive was contained by the German and Austro-Hungarian armies, which counter-attacked and forced the Russian armies to retreat. On the Baltic coast from 1 to 5 September 1917, the Germans attacked with their strategic reserve of six divisions and captured Riga. In Operation Albion (September–October 1917), the Germans took the islands at the mouth of the Gulf of Riga. The British and French commanders on the Western Front had to reckon on the German western army (Westheer) being strengthened by reinforcements from the Ostheer on the Eastern Front by late 1917. Haig wished to exploit the diversion of German forces in Russia for as long as it continued and urged the British War Cabinet to commit the maximum amount of manpower and munitions to the battle in Flanders.
Prelude
=== Ypres salient === Ypres is overlooked by Kemmel Hill in the south-west and from the east by a line of low hills running south-west to north-east. Wytschaete (Wijtschate) and Hill 60 are to the east of Verbrandenmolen, Hooge, Polygon Wood and Passchendaele (Passendale). The high point of the ridge is at Wytschaete, 7,000 yd (4.0 mi; 6.4 km) from Ypres, while at Hollebeke the ridge is 4,000 yd (2.3 mi; 3.7 km) distant and recedes to 7,000 yd (4.0 mi; 6.4 km) at Polygon Wood. Wytschaete is about 150 ft (46 m) above the plain; on the Ypres–Menin road at Hooge, the elevation is about 100 ft (30 m) and 70 ft (21 m) at Passchendaele. The rises are slight, apart from the vicinity of Zonnebeke, which has a gradient of 1:33. From Hooge and further east, the slope is 1:60 and near Hollebeke, it is 1:75; the heights are subtle and resemble a saucer lip around the city. The main ridge has spurs sloping east and one is particularly noticeable at Wytschaete, which runs 2 mi (3.2 km) south-east to Messines (Mesen) with a gentle slope on the east side and a 1:10 decline westwards. Further south, is the muddy valley of the River Douve, Ploegsteert Wood (Plugstreet to the British) and Hill 63. West of Messines Ridge is the parallel Wulverghem (Spanbroekmolen) Spur and on the east side, the Oosttaverne Spur, which is also parallel to the main ridge. The general aspect south and east of Ypres, is one of low ridges and dips, gradually flattening northwards beyond Passchendaele, into a featureless plain. Possession of the higher ground to the south and east of Ypres, gives an army ample scope for ground observation, enfilade fire and converging artillery bombardments. An occupier also has the advantage that artillery deployments and the movement of reinforcements, supplies and stores can be screened from view. The ridge had woods from Wytschaete to Zonnebeke giving good cover, some being of notable size, like Polygon Wood and those later named Battle Wood, Shrewsbury Forest and Sanctuary Wood. In 1914, the woods usually had undergrowth but by 1917, artillery bombardments had reduced the woods to tree stumps, shattered tree trunks tangled with barbed wire and more wire festooning the ground, which was full of shell-holes; fields in the gaps between the woods were 800–1,000 yd (730–910 m) wide and devoid of cover. The main road to Ypres from Poperinge to Vlamertinge is in a defile, easily observed from the ridge. Roads in the area were unpaved, except for the main ones from Ypres, with occasional villages and houses dotted along them. 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.
Topography
In Flanders, sands, gravels and marls predominate, covered by silts in places. The coastal strip is sandy but a short way into the hinterland, the ground rises towards the Vale of Ypres, which before 1914 was a flourishing market garden. Ypres is 66 ft (20 m) above sea level; Bixschoote 4 mi (6.4 km) to the north is at 28 ft (8.5 m). To the east the land is at 66–82 ft (20–25 m) for several miles, with the Steenbeek river at 49 ft (15 m) near St Julien. There is a low ridge from Messines, 260 ft (80 m) at its highest point, running north-east past Clapham Junction at the west end of Gheluvelt plateau (2+1⁄2 miles from Ypres at 213 ft (65 m) and Gheluvelt, above 160 ft (50 m) to Passchendaele, (5+1⁄2 miles from Ypres at 160 ft (50 m) declining from there to a plain further north. Gradients vary from negligible, to 1:60 at Hooge and 1:33 at Zonnebeke. Underneath the soil is London clay, sand and silt; according to the Commonwealth War Graves Commission categories of sand, sandy soils and well-balanced soils, Messines ridge is well-balanced soil and the ground around Ypres is sandy soil. The ground is drained by many streams, canals and ditches, which need regular maintenance. Since 1914 much of the drainage had been destroyed, though some parts were restored by land drainage companies from England. The British considered the area drier than Loos, Givenchy and Plugstreet Wood further south. A study of weather data recorded at Lille, 16 mi (26 km) from Ypres from 1867–1916, published in 1989, showed that August was more often dry than wet, that there was a trend towards dry autumns (September–November) and that average rainfall in October had decreased since the 1860s.
=== British plans === Preparations for operations in Flanders began in 1915, with the doubling of the Hazebrouck–Ypres rail line and the building of a new line from Bergues to Proven, which was doubled in early 1917. Progress on roads, rail lines, railheads and spurs in the Second Army zone was continuous and by mid-1917, gave the area the most efficient supply system of the BEF. Several plans and memoranda for a Flanders offensive were produced between January 1916 and May 1917, in which the writers tried to relate the offensive resources available to the terrain and the likely German defence. In early 1916, the importance of the capture of the Gheluvelt plateau for an advance further north was emphasised by Haig and the army commanders. On 14 February 1917, Colonel Norman MacMullen of GHQ proposed that the plateau be taken by a massed tank attack, reducing the need for artillery; in April a reconnaissance by Captain Giffard LeQuesne Martel found that the area was unsuitable for tanks. On 9 February, Rawlinson, commander of the Fourth Army, suggested that Messines Ridge could be taken in one day and that the capture of the Gheluvelt plateau should be fundamental to the attack further north. He suggested that the southern attack from St Yves to Mont Sorrel should come first and that Mont Sorrel to Steenstraat should be attacked within 48 to 72 hours. After discussions with Rawlinson and Plumer and the incorporation of Haig's changes, Macmullen submitted his memorandum on 14 February. With amendments the memorandum became the GHQ 1917 plan. A week after the Battle of Messines Ridge, Haig gave his objectives to his army commanders, the wearing out of the enemy, securing the Belgian coast and connecting with the Dutch frontier by capturing Passchendaele ridge, followed by an advance on Roulers and Operation Hush, an attack along the coast with a combined amphibious landing. If manpower and artillery were insufficient, only the first part of the plan might be fulfilled. On 30 April, Haig told Gough, the Fifth Army commander, that he would lead the Northern Operation and the coastal force, although Cabinet approval for the offensive was not granted until 21 June.
German defences
The 4th Army held a front of 25 mi (40 km) with three Gruppen, composed of a corps headquarters and a varying complement of divisions; Group Staden, based on the headquarters of the Guards Reserve Corps was added later. Group Dixmude held 12 mi (19 km) with four front divisions and two Eingreif divisions, Group Ypres held 6 mi (9.7 km) from Pilckem to Menin Road with three front divisions and two Eingreif divisions and Group Wijtschate held a similar length of front south of the Menin road, with three front divisions and three Eingreif divisions. The Eingreif divisions were stationed behind the Menin and Passchendaele ridges. About 5 mi (8.0 km) further back, were four more Eingreif divisions and 7 mi (11 km) beyond them, another two in OHL reserve. The Germans were anxious that the British would attempt to exploit the victory of the Battle of Messines, with an advance to the Tower Hamlets spur beyond the north end of Messines Ridge. On 9 June, Crown Prince Rupprecht proposed a withdrawal to the Flandern line east of Messines. Construction of defences began but was terminated after Fritz von Loßberg was appointed Chief of Staff of the 4th Army. Loßberg rejected the proposed withdrawal to the Flandern line and ordered that the front line east of the Oosttaverne line be held rigidly. The Flandernstellung (Flanders Position) along Passchendaele Ridge, in front of the Flandern line, would become Flandern I Stellung and a new position, Flandern II Stellung, would run west of Menin, northwards to Passchendaele. Construction of a Flandern III Stellung east of Menin northwards to Moorslede was also begun. From July 1917, the area east of Ypres was defended by the front position, the Albrechtstellung (second position), Wilhelmstellung (third position), Flandern I Stellung (fourth position), Flandern II Stellung (fifth position) and Flandern III Stellung, the sixth position (incomplete). Between the German defences lay villages such as Zonnebeke and Passchendaele, which were fortified and prepared for all-round defence. On 25 June, Erich Ludendorff, the First Quartermaster General, suggested to Crown Prince Rupprecht that Group Ypres should withdraw to the Wilhelmstellung, leaving only outposts in the Albrechtstellung. On 30 June, the army group Chief of Staff, General von Kuhl, suggested a withdrawal to the Flandern I Stellung along Passchendaele ridge, meeting the old front line in the north near Langemarck and Armentières in the south. Such a withdrawal would avoid a hasty retreat from Pilckem Ridge and force the British into a time-consuming redeployment. Loßberg disagreed, believing that the British would launch a broad front offensive, that the ground east of the Sehnenstellung was easy to defend and that the Menin road ridge could be held if it was made the Schwerpunkt (point of main effort) of the German defensive system. Pilckem Ridge deprived the British of ground observation over the Steenbeek Valley, while the Germans could see the area from Passchendaele Ridge, allowing German infantry to be supported by observed artillery-fire. Loßberg's judgement was accepted and no withdrawal was made.
Battle of Messines
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. Since mid-1915, the British had been mining under the German positions on the ridge and by June 1917, 21 mines had been filled with nearly 1,000,000 lb (454 t) of explosives. The Germans knew the British were mining and had taken counter-measures but they were surprised at the extent of the British effort. Two of the mines failed to detonate but 19 went off on 7 June, at 3:10 a.m. British Summer Time. The final objectives were largely gained before dark and the British had fewer losses than the expected (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. 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.
Battles
July–August
Haig selected Gough to command the offensive on 30 April and on 10 June Gough and the Fifth Army headquarters took over the Ypres salient north of Messines Ridge. Gough planned an offensive based on the GHQ 1917 plan and the instructions he had received from Haig. Gough held meetings with his corps commanders on 6 and 16 June, where the third objective, which included the Wilhelmstellung (third line), a second-day objective in earlier plans, was added to the two objectives due to be taken on the first day. A fourth objective, the red line, was also given for the first day, to be attempted by fresh troops, at the discretion of divisional and corps commanders, in places where the German defence had collapsed. The attack was not planned as a breakthrough operation and Flandern I Stellung, the fourth German defensive position, lay 10,000–12,000 yd (5.7–6.8 mi; 9.1–11.0 km) behind the front line and was not an objective on the first day. The Fifth Army plan was more ambitious than the plans devised by Rawlinson and Plumer, which had involved an advance of 1,000–1,750 yd (910–1,600 m) on the first day, by compressing their first three attacks into one day instead of three. Major-General John Davidson, Director of Operations at GHQ, wrote in a memorandum that there was "ambiguity as to what was meant by a step-by-step attack with limited objectives" and suggested reverting to a 1,750 yd (1,600 m) advance on the first day to increase the concentration of British artillery. Gough stressed the need to plan to exploit opportunities to take ground left temporarily undefended, more likely in the first attack, which would have the benefit of long preparation. This had not been done in earlier battles and vacant ground, there for the taking, had been re-occupied by the Germans. At the end of June, Haig added a division to II Corps (Lieutenant-General Claud Jacob) from the Second Army and next day, after meeting with Gough and General Herbert Plumer, the Second Army commander, Haig endorsed the Fifth Army plan.
Battle of Pilckem Ridge
The British attack began at 3:50 a.m. on 31 July; the attack was to commence at dawn but a layer of unbroken low cloud meant that it was still dark when the infantry advanced. The main attack, by II Corps across the Ghelveult Plateau to the south, confronted the principal German defensive concentration of artillery, ground-holding divisions (Stellungsdivisionen) and Eingreif (counter-attack) divisions. The attack had most success on the northern flank, on the fronts of XIV Corps and the French First Army, both of which advanced 2,500–3,000 yd (1.4–1.7 mi; 2.3–2.7 km) to the line of the Steenbeek river. In the centre, XVIII Corps and XIX Corps pushed forward to the line of the Steenbeek (black line) to consolidate and sent fresh troops towards the green line. On the XIX Corps front fresh troops advanced to the red line, for a move forward of about 4,000 yd (3,700 m). Group Ypres counter-attacked the flanks of the British break-in, supported by every artillery piece and aircraft within range, around noon. The Germans were able to drive the three British brigades back to the black line with 70 per cent casualties; the German advance was stopped at the black line by mud, artillery and machine-gun fire.
Capture of Westhoek
After rain delays from 2 August, II Corps attacked again on 10 August, to capture the rest of the black line (second objective) on the Gheluvelt plateau. The infantry advance succeeded but German artillery-fire and infantry counter-attacks isolated the infantry of the 18th (Eastern) Division in Glencorse Wood. At about 7:00 p.m., German infantry attacked behind a smokescreen and recaptured all but the north-west corner of the wood; only the 25th Division gains on Westhoek Ridge to the north were held. Lieutenant-Colonel Albrecht von Thaer, Chief of Staff of Gruppe Wijtschate (Group Wytschaete, the headquarters of the IX Reserve Corps), noted that casualties after 14 days in the line averaged 1,500–2,000 men, compared to 4,000 men on the Somme in 1916 and that German troop morale was higher than the year before.
Battle of Hill 70
Attacks to threaten Lens and Lille were to be made by the First Army in late June near Gavrelle and Oppy, along the Souchez river. The objective was to eliminate a German salient between Avion and the west end of Lens, by taking reservoir Hill (Hill 65) and Hill 70. The attacks were conducted earlier than planned to use heavy and siege artillery before it was transferred to Ypres, the Souchez operation being cut back and the attack on Hill 70 postponed. The Battle of Hill 70, 30 mi (48 km) south of Ypres, eventually took place from 15 to 25 August. The Canadian Corps fought four divisions of the German 6th Army in the operation. The capture of Hill 70 was a costly success in which three Canadian divisions inflicted many casualties on the German divisions opposite and pinned down troops reserved for the relief of tired divisions in Flanders. Hermann von Kuhl, chief of staff of Army Group Crown Prince Rupprecht, wrote later that it was a costly defeat and wrecked the plan for relieving fought-out (exhausted) divisions in Flanders.
Battle of Langemarck
The Battle of Langemarck was fought from 16 to 18 August; the Fifth Army headquarters was influenced by the effect that delay would have on Operation Hush, which needed the high tides due at the end of August or it would have to be postponed for a month. Gough intended that the rest of the green line, just beyond the Wilhelmstellung (German third line), from Polygon Wood to Langemarck, was to be captured and the Steenbeek crossed further north. In the II Corps area, the disappointment of 10 August was repeated, with the infantry managing to advance, then being isolated by German artillery and forced back to their start line by German counter-attacks, except in the 25th Division area near Westhoek. Attempts by the German infantry to advance further were stopped by British artillery-fire with many casualties. The advance further north in the XVIII Corps area retook and held the north end of St Julien and the area south-east of Langemarck, while XIV Corps captured Langemarck and the Wilhelmstellung north of the Ypres–Staden railway, near the Kortebeek stream. The French First Army conformed, pushing up to the Kortebeek and St Jansbeck stream west of the northern stretch of the Wilhelmstellung, where it crossed to the east side of the Kortebeek.
Local attacks
The Germans continued to inflict losses on the British divisions beyond Langemarck but on 19 August, after two fine dry days, XVIII Corps conducted a novel combined arms operation with infantry, tanks, aircraft and artillery. German strongpoints and pillboxes along the St Julien–Poelcappelle road in front of the Wilhelmstellung were captured. On 22 August, more ground was gained by XIX and XVIII corps but the Germans on the Gheluvelt Plateau remained. Another attack by II Corps on the Gheluvelt Plateau (22 to 24 August) failed in fighting that was costly to both sides. Gough laid down a new infantry formation of skirmish lines to be followed by "worms" on 24 August and Cavan noted that pillboxes should be attacked on a broad front to engage them simultaneously. Another general offensive, intended for 25 August, was delayed by the failure of the preliminary attacks and then postponed due to more bad weather. On 27 August, II Corps tried a combined tank and infantry attack but the tanks bogged, the attack failed and Haig called a halt to operations until the weather improved.
Weather
In Field Marshal Earl Haig (1929), Brigadier-General John Charteris, the BEF Chief of Intelligence from 1915 to 1918, wrote that
Careful investigation of records of more than eighty years showed that in Flanders the weather broke early each August with the regularity of the Indian monsoon: once the Autumn rains set in difficulties would be greatly enhanced....Unfortunately, there now set in the wettest August for thirty years. only the first part of which was quoted by Lloyd George (1934), Liddell Hart (1934) and Leon Wolff (1959). In a 1997 essay, John Hussey called the passage by Charteris "baffling". The BEF had set up a Meteorological Section under Ernest Gold in 1915, which by the end of 1917 had 16 officers and 82 men. The section predicted the warm weather and thunderstorms of 7 to 14 June; in a letter to the press of 17 January 1958, Gold wrote that the facts of the Flanders climate contradicted Charteris. In 1989, Philip Griffiths examined August weather in Flanders for the thirty years before 1916 and found that,
...there is no reason to suggest that the weather broke early in the month with any regularity. From 1901 to 1916, records from a weather station at Cap Gris Nez showed that 65 per cent of August days were dry and that from 1913 to 1916, there were 26, 23, 23 and 21 rainless days and monthly rainfall of 17, 28, 22 and 96 mm (0.67, 1.10, 0.87 and 3.78 in);
...during the summers preceding the Flanders campaign August days were more often dry than wet. There were 127 mm (5.0 in) of rain in August 1917 and 84 mm (3.3 in) of the total fell on 1, 8, 14, 26 and 27 August. The month was overcast and windless, which much reduced evaporation. Divided into two ten-day and an eleven-day period, there were 53.6, 32.4 and 41.3 mm (2.11, 1.28 and 1.63 in) of rain; in the 61 hours before 6:00 p.m. on 31 July, 12.5 mm (0.49 in) fell. From 6:00 p.m. on 31 July to 6:00 p.m. on 4 August, there was another 63 mm (2.5 in) of rain. August 1917 had three dry days and 14 days with less than 1 mm (0.039 in) of rain. Three days were sunless and one had six minutes of sunshine; from 1 to 27 August there were 178.1 hours of sunshine, an average of 6.6 hours per day. Hussey wrote that the wet weather in August 1917 was exceptional and that Haig had been justified in expecting little rain and that it would be dried swiftly by sunshine and breezes.
