'David' (i) was the deployment of General the Lord Gort’s British Expeditionary Force from north-eastern France into Belgium at the start of the 'Battle of Belgium' as the Germans invaded that country in 'Gelb' (10/24 May 1940).

On the day that the Germans began their invasion of neutral Belgium, the British Expeditionary Force moved forward from its prepared defences on the Franco-Belgian border to take up a new position deep inside Belgium, conforming to plans made by the French high command. Forming a defensive line with French and Belgian forces to its south and north respectively, the British Expeditionary Force was able to contain attacks by German infantry divisions, but was unaware that this German thrust was essentially a strategic diversion to support the main thrust by German armoured divisions farther to the south in 'Sichelschnitt'. To avoid complete encirclement, the British Expeditionary Force and its allies were forced into a series of fighting retreats that ended back at their initial border positions by 24 May. However, by this date the German armoured spearhead had reached the southern coast of the English Channel behind them, cutting them off from their supply chain and the larger part of the French forces, and leading to the Dunkirk evacuation of the British Expeditionary Force and some Allied troops in 'Dynamo' during the following days.

In the period between the two world wars, French military planners had adopted the idea of fortifying France’s borders, and work on the resulting 'Ligne Maginot' had begun in 1930. In 1932, the Conseil Supérieur de la Guerre had decided that France’s north-eastern border should not be fortified, for the low-lying nature of the terrain made building suitable structures technically difficult and France had been in a military alliance with Belgium since 1920. It was therefore decided that France could best be protected against any German aggression in the region by defending Belgium: for the French, this had the advantage that any fighting would not be on French soil, thus preserving the important industrial towns in the border area. The strategy received a setback in 1936 when Belgium declared its neutrality and abandoned its military alliance with France, meaning that in the event of a German invasion, the French and Belgian armies could no longer co-ordinate their defence plans.

The French planners had identified three possible defensive lines inside Belgium. The most obvious was the Albert Canal, which runs inside the Belgian border with Germany: since the declaration of Belgian neutrality, however, it seemed likely that French forces would be able to move into Belgian territory only after an invasion had begun, and in that case, there would be insufficient time to deploy before the line had been overrun. The second possibility was the line of the Scheldt river, known to the French as the Escaut river, which runs through Ghent to Antwerp. Although the Escaut is a formidable natural obstacle, defending this river line, in an option known as the 'Escaut Plan' or 'Plan E', would entail abandoning to the Germans large amounts of Belgian territory including Brussels and other major industrial areas. The final possibility was to establish a line along the course of the Dyle river in the 'Dyle Plan' or 'Plan D'. Although this would preserve more Belgian assets and the line was shorter than the Escaut line, the river itself is considerably smaller and hardly bigger than a stream in some places, and therefore represents a position considerably more difficult to defend. Furthermore, the Dyle river does not extend all the way to the Meuse river, thereby creating an unbroken line, and to the east of the town of Wavre there is the so-called 'Gembloux gap', a 25-mile (40-km) plain without any natural obstacles.

On deployment to France in September 1939, the British Expeditionary Force was incorporated into Général d’Armée Gaston Billotte’s 1er Groupe d’Armées, which was responsible for the defence of France along the Belgian and Luxembourgeois borders from the English Channel coast to the northern end of the 'Ligne Maginot'. Also part of this army group were Général d’Armée Georges Maurice Jean Blanchard’s 1ème Armée and Général d’Armée André Corap’s 9ème Armée. All these forces were under the overall command of the commander-in-chief of the North-Eastern Front, Général d’Armée Alphonse Joseph Georges. The section of the Franco-Belgian border to be held by the British Expeditionary Force stretched from Armentières westward toward Menin and then south to the point at which the border met the Escaut river at Maulde, forming a salient around Lille and Roubaix. The British began to fortify their sector with trenches, weapon pits and pillboxes in what became known as the Gort Line.

Initially, Général d’Armée Maurice Gamelin, the French commander-in-chief, had favoured 'Plan E', and in a directive of 24 October 1939 had stated that an advance to the Dyle could only be considered if the 1er Groupe d’Armées was able to deploy into Belgium before a German attack. Meanwhile, the Belgians had tentatively begun to fortify the Dyle Line, known to them as the 'Ligne Koningshooikt-Wavre', which brought about a change in Gamelin’s opinion, despite opposition from Georges, who was more cautious. On 9 November, a meeting of Allied commanders at Vincennes agreed to the adoption of 'Plan D', and this was confirmed at a meeting of the Supreme War Council on 17 November. The British were dubious about any advance into Belgium but, given the comparatively small size of the British Expeditionary Force, Gort felt that he had little option but to concur.

In January 1940, in the 'Mechelen incident', a German aeroplane carrying a copy of the invasion plan crash-landed in Belgium. Examination of this plan confirmed Gamelin’s suspicions that the Germans would attempt a reiteration of the 1914 Schlieffen Plan by attacking through Belgium, but also revealed that the Germans were planning to occupy part of the neutral Netherlands, a possibility which Gamelin had previously suggested. Perhaps influenced by this intelligence, in March Gamelin revised 'Plan D' with the 'Breda Variant' in which Général d’Armée Henri Giraud’s 7ème Armée, was to be removed from reserve at Rouen and placed on the border to the left of the British Expeditionary Force. In the event of invasion, the 7ème Armée was to move swiftly to the north and link with Dutch forces at Breda, where it would protect the approaches to Antwerp from falling into German hands. In the final version of the plan, the Belgians were expected to delay a German advance, then retire from the Albert Canal to the Dyle river between Antwerp and Louvain. On the Belgian right, the British Expeditionary Force was to defend about 12 miles (20 km) of the Dyle river between Louvain and Wavre with nine divisions, and the 1ère Armée on the right of the British Expeditionary Force, was to hold 22 miles (35 km) from Wavre across the 'Gembloux gap' to Namur with 10 divisions. The 9ème Armée was to take position to the south of Namur, along the Meuse river to the northern flank of the 2ème Armée.

By March 1940, the British Expeditionary Force had doubled in size to 394,165 men since its original deployment. Within a short time, the British Expeditionary Force’s order of battle comprised 10 infantry divisions in Lieutenant General M. G. H. Barker’s I Corps, Lieutenant General A. F. Brooke’s II Corps and Lieutenant General Sir Ronald Adam’s III Corps, Air Vice Marshal C. H. B. Blount’s Air Component Royal Air Force detachment of about 500 aircraft and Air Vice Marshal P. H. L. Playfair’s Advanced Air Striking Force long-range bomber force. These were commanded by General Headquarters, which held a reserve of headquarters troops including Major General H. E. Franklyn’s 5^th Division, Brigadier D. H. Pratt’s 1^st Army Tank Brigade and Brigadier C. W. Norman’s 1^st Light Armoured Reconnaissance Brigade, as well as artillery, signals, pioneers, logistic and medical units.

From 01.00 on 10 May, the French national headquarters, the Grand Quartier Général, received information from Brussels and Luxembourg that the German invasion was about to begin, and at 04.35 the German invasion of the Low Countries and France started. Gamelin was woken at 06.30 and ordered the launch of the 'Dyle Plan', and 'David' started the British part of the 'Dyle Plan'. The British vanguard, spearheaded by the armoured cars of the 12^th Royal Lancers, crossed the border at 13.00 on 10 May, cheered on by crowds of Belgian civilians lining the route. The section of the Dyle river which had been allocated to the British Expeditionary Force extended from Louvain to the south-west toward Wavre, a distance of some 22 miles (35 km). Gort had decided to commit in the first line only three formations, namely the 3^rd Division from II Corps in the north with 1^st Division and 2^nd Division from I Corps farther to the south, leaving some battalions to defend a frontage double that recommended by British Army field manuals. The British Expeditionary Force had sufficient motor transport to move the three front-line divisions in a movement intended to be completed in 90 hours. The other divisions of the British Expeditionary Force were positioned for the provision of defence in depth all the way back to the Escaut river, and had to march toward their positions until motor transport could be made available.

On arrival at the river to the north of Louvain, the 3^rd Division found that part of its allotted position was already occupied by Belgian troops, who refused to move for their British allies, even though Brooke appealed directly to the King of the Belgians, and finally had to be directly ordered out by Georges. The British infantry battalions posted along the bank of the Dyle river began to arrive on 11 May and started to dig trenches: the defences previously constructed by the Belgians amounted to only a few scattered pillboxes and some barbed wire. These preparations were protected by a screen of light tanks and Bren Gun Carriers operating on the western side of the river to keep German reconnaissance patrols away, and were withdrawn on 14 May when all the front-line units were in place and the bridges had been blown.

The first German forces reached the British Expeditionary Force’s front during the afternoon of 14 May, when reconnaissance troops of three German infantry divisions arrived in motor cars or on motorcycles. They were apparently unaware of the British positions and in several places approached the Dyle river without taking cover and were thus easy targets for British small arms and artillery fire. Later in the evening, parts of the line were engaged by German field artillery, the first experience for many British troops of German fire. Organised German attacks started on 15 May, when assaults on Louvain by Generalmajor Otto von Knobelsdorff’s 19^th Division of the 6^th Army's XI Corps were repulsed by the 3^rd Division. On the left of the division’s line, the 1/Grenadier Guards was forced to abandon its forward positions and withdraw behind the Dyle Canal, which runs a short distance to the west of the river, but there the line held. At dawn on the following day, after a two-hour barrage, a determined German attack was made on Louvain railway station and the adjacent goods yard, but after a prolonged fight, the Germans were thrown back in a counterattack by the 1/Royal Ulster Rifles and the 1/King’s Own Scottish Borderers. Farther to the south, the river is only about 15 ft (4.6 m) wide, and while this prevented tanks from crossing, it was a less effective barrier to a determined infantry assault. All the German bridgeheads across the Dyle river were either repulsed or effectively contained by British counterattacks, but by the morning of 16 May, events far to the south had led to Gort’s receipt of orders to withdraw the British Expeditionary Force to the Escaut river.

The 7ème Armée drove forward on the northern flank and advanced elements reached Breda on 11 May. They found that the Moerdijk bridges had been captured by German paratroopers, cutting the link between the southern and northern parts of the Netherlands and forcing the Dutch army to retire to the north in the direction of Amsterdam and Rotterdam. The French collided with Generalleutnant Alfred Ritter von Hubicki’s 9^th Panzerdivision, and the advance of the 25ème Division d’Infanterie Motorisée was stopped by German infantry, tanks and Junkers Ju 87 single-engined dive-bombers as the 1ère Division Légère Mécanisée was forced to retreat. (All the French heavy tanks were still on trains to the south of Antwerp.) The 'Breda Variant' of Gamelin’s plan had been thwarted in fewer than two days and on 12 May, Gamelin ordered the 7ème Armée to cancel the plan and cover Antwerp. On 12 May, the 7ème Armée fell back from the line between Bergen-op-Zoom and the Turnhout Canal, some 20 miles (32 km) from Antwerp, to Lierre, 10 miles (16 km) away. Two days later, on 14 May, the Dutch surrendered.

In Belgium, the Albert Canal defence line was based on the fortress of Eben-Emael and was broken when German gliderborne troops landed on the roof in 'Granit' and captured it by 12.00 on 11 May; two bridges over the Maas river were captured at Maastricht. The disaster forced the Belgian army to retreat toward the line between Antwerp and Louvain on 12 May, far too soon for the 1ème Armée to arrive and dig in. Général de Corps d’Armée René Jacques Adolphe Prioux’s French Corps de Cavalerie had reached the 'Gembloux gap' on 11 May and officers reported that the area had been far less fortified by the Belgians than expected: no anti-tank defences had been built and there were no trenches or concrete fortifications; there were some cointet-elements (steel barriers) but none of the anti-tank mines supposed to protect them. Some of the cointet-elements were so poorly sited that a French officer enquired if the Germans had been asked where to site them. Prioux tried to persuade Billotte and Georges to scrap the 'Dyle Plan' and revert to the 'Escaut Plan': with the 1er Groupe d’Armées on the move, Georges decided against changing the plan, but Blanchard was ordered to accelerate the 1ème Armée’s advance so as to arrive one day early on 14 May.

On 15 May, the Germans attacked the 1ème Armée along the 'Dyle Line', triggering the meeting engagement which Gamelin had tried to avoid. The 1ème Armée repulsed General Erich Hoepner’s XVI Corps (mot.) during the 'Battle of the Gembloux Gap' on 14/15 May), but GQG realised too late that the attack they were facing was a diversion: the main German attack had come farther to the south, where Heeresgruppe 'B' had burst through the lightly defended Ardennes.

On 16 May, the 1er Groupe d’Armées was ordered to retreat from the 'Dyle Line' in order to avoid being trapped by the German breakthrough against the 2ème Armée and 9ème Armée, but on 20 May the Germans reached Abbeville on the English Channel coast, cutting off the northern armies.

The plan for the British Expeditionary Force’s withdrawal was that under cover of darkness units would thin their fronts and make a phased and orderly withdrawal before the Germans realised what was happening. The objective for the night of 16/17 May was the Charleroi to Willebroek Canal (known to the British Expeditionary Force as the Line of the Senne), the following night to the Dendre river between Maubeuge and Termonde, and the Escaut river and Antwerp (the Dendre Line), and finally on 18/19 May to the Escaut river between Oudenarde and Maulde on the French border (the Escaut Line). The order to withdraw was greeted with astonishment and frustration by the British troops, who felt that they had held their own, but they were unaware of the deteriorating situation elsewhere. Fortunately, the British Expeditionary Force’s training had included the complicated task of withdrawal while in contact with the enemy. Starting at 21.00 and under the cover of an intense bombardment by the British artillery, which expended its stockpiled ammunition, the withdrawal proceeded largely to plan. On the far left of the British line, the situation was complicated by the early withdrawal of the neighbouring Belgians, allowing the Germans to pass around the flank of 1/Coldstream Guards and occupy the town of Herent, which lay on the withdrawal route; hard fighting, including a bayonet charge, was required to clear the road, at a cost of 120 guardsmen. The last units to leave the line were the divisional cavalry regiments in their light tanks and carriers. A later communication breakdown caused a total loss of co-ordination with the Belgian army to the north-west of the II Corps, and a dangerous gap opened between the two; fortunately it was covered by British light armour before the Germans could discover and exploit it.

On the British sector of the Escaut river, the British Expeditionary Force deployed in the front line, from north to south, the 44^th Division, 4^th Division, 3^rd Division, 1^st Division, 42^nd Division, 2^nd Division and 48^th Division. The British divisions faced nine German infantry divisions, which began their attack on the morning of 21 May with a devastating artillery barrage. Shortly after this, infantry assaults started along the whole front, crossing the canalised river either in inflatable boats or by clambering across the wreckage of demolished bridges. Although the Escaut Line was penetrated in numerous places, all the German bridgeheads were either thrown back or contained by vigorous but costly British counterattacks, and the remaining German troops were ordered to retire across the river by the night of 22 May.

In a meeting between Gort and his corps commanders on 22 May, it was agreed that the Escaut Line could not be held for long and a withdrawal was planned for the night of 23/24 May. In the meantime, in a chaotic series of meetings at Ypres, Général d’Armée Maxime Weygand, who had recently replaced Gamelin as the French commander-in-chief, proposed to King Leopold and Billotte a new defensive line in which the Belgians would defend the Lys river while on 23/24 May the British withdrew to the border defences, the so-called Gort Line, which it was hoped would allow the British Expeditionary Force to attack to the south at the vulnerable flank of Heeresgruppe 'A' on 26 May. Weygand had hoped that the Belgians would retire to the shorter defensive line of the Yser river, as they had in 1914, but Leopold was unwilling to abandon so much Belgian soil and perhaps, viewed in retrospect, indicating that he had no intention of fighting a prolonged campaign. Although Gort knew that the meeting had been planned, a communication breakdown at his headquarters meant that he knew neither the time nor the location, and was finally located by Belgian staff officers. Weygand had left before Gort arrived, believing that Gort had been absent deliberately. In a final meeting, Weygand’s plan was agreed without Gort being able to explain the difficulties to him. Billotte was fatally injured in a road accident on his way back to his headquarters, resulting further confusion.

Starting on 17 May, Gort began to improvise formations in an effort to shield the British Expeditionary Force’s exposed southern flank from Heeresgruppe 'B'. These forces used the canal from Gravelines on the coast through St Omer, Béthune and La Bassée, known as the Canal Line. Forward of this line, the town of Arras was being held by a determined British garrison and in order to support it, a modest force led by Gott’s only heavy armour, the 1^st Army Tank Brigade, attacked to the south on 21 May. Although the 'Battle of Arras' came as a shock to the Germans, it achieved little.

The withdrawal from the Escaut Line proceeded smoothly on the southern end of the line, with light armour again providing an effective rearguard. However, in the north, the 44^th Division had difficulty contacting all its units. Since there were no radios below battalion level and the field telephone lines had been disrupted by heavy shelling and bombing, messages had to be sent by runners or in vehicles, many of which fell victim to German fire. For the first time in the campaign, the Germans continued to push forward at night, and the 44^th Division and the neighbouring 4^th Division had to fight their way out.

On 24 May, the British Expeditionary Force was back where it had started in 'David' (i), but now had the Germans behind them as well as in front, and was cut off from its supplies: the men had been placed on half-rations during the previous day. Additionally, nearly all of the RAF Air Component had been withdrawn to England, making the provision of air support even more difficult and, moreover, much of the air effort had been diverted to the support the fighting at Boulogne and Calais. The shorter front and better defences at the frontier allowed Gort to move the 2^nd Division and 48^th Division toward Lille to reinforce the defence of the Canal Line. On 25 May, with the need to evacuate now evident, Brooke’s II Corps was ordered to form a defensive line on the Ypres-Comines Canal in order to create a protected corridor along which the British Expeditionary Force’s main body could withdraw toward the coast at the start of the 'Battle of Dunkirk'.