The 'Battle of Dunkirk' was fought between German and Allied forces around the north-eastern French port of Dunkirk (Dunkerque in French) as the Allies were losing the 'Battle of France' and seeking to extract their northern forces to the UK (26 May/4 June 1940).

After the 'Phoney War' of September 1939 to a time early in May 1940, the 'Battle of France' began in earnest on 10 May 1940 as the German launched their 'Gelb' and 'Sichelschnitt' undertakings against the Low Countries and France respectively. In the north-east, Generaloberst Fedor von Bock’s Heeresgruppe 'B' invaded the Netherlands and Belgium, and advanced to the west. In response, the Allied supreme commander, the French Général d’Armée Maurice Gamelin, initiated 'Plan D' in which French and British troops entered Belgium to engage the Germans in the Netherlands. French planning for war relied on the 'Ligne Maginot' fortifications along the French/German border to protect the Lorraine region, but these defences did not cover the Belgian border. German forces had already crossed most of the Netherlands before the French and British forces had arrived, so Gamelin instead committed the forces under his command (three mechanised forces in the form of the French 1ère Armée and 7ème Armée, and the British Expeditionary Force) to the defence of Dyle river line. Farther to the south, on 14 May Generaloberst Gerd von Rundstedt’s Heeresgruppe 'A' burst through the Ardennes and advanced rapidly westward to the area of Sedan, crossing the Meuse river and advancing to the west and then to the the north-west to reach the southern coast of the English Channel, using Generalleutnant Erich von Manstein’s 'Sichelschnitt' plan thereby outflanking the Allies' northern group of forces.

A series of Allied counterattacks, including the 'Battle of Arras', failed to sever the German spearhead, which advanced through the 'Panzer corridor' to reach the southern coast of the English Channel on 20 May, there by separating the British Expeditionary Force near Armentières, the French 1ère Armée and the Belgian army farther to the north from the majority of French troops operating to the south of the German penetration. After reaching the coast of the English Channel, the German forces swung to the north-east along the coast, threatening to capture its ports and trap the British and French forces.

In one of the most debated decisions of World War II, the Germans halted their advance on Dunkirk. What became known as the 'Halt Order' did not originate with Adolf Hitler: von Rundstedt and Generaloberst Günther von Kluge, the latter commanding the primary armoured forces under von Rundstedt’s overall command, suggested that the German forces around what was now the Dunkirk pocket should bring their advance on the port to a halt and consolidate to prevent any Allied break-out. Hitler approved the concept on 24 May with the support of the Oberkommando der Wehrmacht: the German armies in the north were to halt for three days, and this provided the Allies with sufficient time to organise the 'Dynamo' evacuation from Dunkirk and create a line to defend this and two smaller ports as more than 330,000 Allied troops were rescued. The French and British sustained heavy casualties and were forced to abandon nearly all their equipment, and some 16,000 French and 1,000 British soldiers died during the evacuation. The British Expeditionary Force alone had lost some 68,000 soldiers during the French campaign.

By 26 May, the British Expeditionary Force and the French 1ère Armée were bottled up in a corridor to the sea, about 60 miles (97 km) deep and 15 miles (24 km) wide. This perimeter extended southward from a north-eastern end on the coast of the English Channel to the north-east of the Belgian city of Bruges as far as a point to the west of Ghent, where its bent to the south-west on the north side of the Lys river to a point between Menin and Ypres, south the sort distance to Comines, south-east toward Valenciennes with a German salient toward the area of Lille in its centre, south-west toward Denain and Douai, and finally to the north-west to reach the southern coast of the English Channel at Gravelines.

Most of the British forces were still located around Lille, more than 40 miles (64 km) from Dunkirk, with the French still farther to the south, and the Belgians to the north-east. These Allied forces were flanked by two major German formations in the form of the infantry-heavy Heeresgruppe B' to their east and the armour-heavy Heeresgruppe 'A' to their west.

On 24 May, Hitler visited von Rundstedt’s headquarters at Charleville. The terrain around Dunkirk was thought to be unsuitable for the commitment of armour, and von Rundstedt advised Hitler that the infantry should attack the British forces at Arras, where the British had proved capable of significant action, while von Kleist’s armour held the line to the west and south of Dunkirk to pounce on the Allied forces retreating from Heeresgruppe 'B'. Familiar with the marshy terrain of Flanders from his experience in World War I, Hitler agreed, and his subsequent order allowed the Germans to consolidate their gains and prepare for the 'Rot' (iii) advance to the south across the Somme rover to destroy the remaining French forces. The Luftwaffe’s commander, Generalfeldmarschall Hermann Göring, saw this as an opportunity for German air power to destroy the forces in Dunkirk. The Allied forces' destruction was thus initially assigned to the air force while the German infantry organised in Heeresgruppe 'B'. von Rundstedt later called this 'one of the great turning points of the war.'

The true reason for the decision to halt the German armour on 24 May is still debated. One theory is that Hitler and von Rundstedt agreed to conserve the armour for 'Rot' (iii), but it is also possible that the Luftwaffe’s ties to the German régime were closer than those of the army and this contributed to Hitler’s acquiescence to Göring’s request, and another theory, to which few historians have given credence, is that Hitler was still trying to establish diplomatic peace with the UK before the 'Barbarossa' invasion of the USSR. Although after the end of the war von Rundstedt stated his suspicions that Hitler wanted 'to help the British', based on alleged praise of the British empire during a visit to his headquarters, there is little evidence that Hitler wanted to let the Allies escape except for a self-exculpatory statement by Hitler himself in 1945.

Whatever the reasons for Hitler’s decision, the Germans confidently believed that the enveloped Allied troops were doomed. Hitler did not rescind the 'Halt Order' until the evening of 26 May, and the three days of respite thus gained gave a vital breathing space to the Royal Navy to arrange the evacuation of the British and many of the other Allied troops. About 338,000 men were rescued in some 11 days: of these, some 215,000 were British and 123,000 were French, of whom 102,250 escaped in British ships.

On 26 May, Anthony Eden, the British secretary of state for war, told Gort that he might need to 'fight back to the west', and ordered him to prepare plans for the evacuation, albeit without telling the French or the Belgians of the fact. Gort had foreseen the order and preliminary plans were already in hand. The first such plan, for a defence along the Lys Canal, could not be carried out because of German advances on 26 May, with Major General N. M. S. Irwin’s 2^nd Division and Major General G. le Q. Martel’s 50^th Division pinned down, and Major General the Hon. H. R. L. G. Alexander’s 1^st Division, Major General H. E. Franklyn’s 5^th Division and Major General A. F. A. N. Thorne’s 48^th Division under heavy attack. Irwin’s 2^nd Division sustained heavy losses as it tried to keep a corridor open, being reduced to brigade strength in the process, but did succeed in this task; the 1^st Division, Major General B. L. Montgomery’s 3^rd Division, Major General D. G. Johnson’s 4^th Division and Major General W. G. Holmes’s 42^nd Division escaped along the corridor that day, as did about one-third of the 1ère Armée. As the Allies fell back, they disabled their artillery and vehicles and destroyed their stores.

On 27 May, the British fought their back to the Dunkirk perimeter line. The Le Paradis massacre took place on this day, when men of SS-Gruppenführer Theodor Eicke’s SS Division 'Totenkopf' machine gunned 97 British and French prisoners near the La Bassée Canal. The British prisoners were men of the 2/Royal Norfolk Regiment, part of the 2^nd Division’s 4^th Brigade. The SS men lined the prisoners against the wall of a barn and shot them all, although two men survived. Meanwhile, the Luftwaffe dropped bombs and leaflets on the Allied armies. The leaflets showed a map of the situation, and read, in English and French, 'British soldiers! Look at the map: it gives your true situation! Your troops are entirely surrounded – stop fighting! Put down your arms!' To the land- and air-minded Germans, the sea seemed an impassable barrier, so they believed the Allies were surrounded, but to the British the sea was the obvious route to safety.

Besides the Luftwaffe’s bombs, German heavy artillery, which had just arrived within range, also fired high-explosive shells into Dunkirk. By this time, more than 1,000 of the town’s civilians had been killed. The bombardment continued until the evacuation had been completed.

Gort had sent ahead Lieutenant General Sir Ronald Adam, commanding the III Corps, to create the necessary defensive perimeter around Dunkirk, command of the corps passing to Lieutenant General S. R. Wason from the general headquarters staff. Lieutenant General A. F. Brooke, commander of the II Corps, was to conduct a holding action with the 3^rd Division, 4^th Division, 5^th Division and 50^th Division along the Ypres-Comines Canal as far as Yser river, while the rest of the British Expeditionary Force fell back. The 'Battle of Wytschaete', across the border in Belgium, was the toughest action Brooke faced in this role. On 26 May, the Germans made a reconnaissance in force against the British position, and at 12.00 on 27 May launched a full-scale attack with three divisions in the area to the south of Ypres. There followed a confused battle in which the visibility was low because of forested or urban terrain, and communications were poor because the British at that time used no radios below battalion level and the area’s telephone wires had been cut. The Germans used infiltration tactics to get among the British, who were beaten back.

The heaviest fighting was in the 5^th Division’s sector. Still on 27 May, Brooke ordered Montgomery, the 3^rd Division’s commander, to extend his division’s line to the left, thereby freeing the 10^th and 11^th Brigades, both of the 4^th Division, to join the 5^th Division at Messines Ridge. The 10^th Brigade arrived first, to find that the Germans had advanced so far that they were closing on the British field artillery. Between them, the 10^th and 11^th Brigades cleared the ridge of Germans, and by 28 May the British were securely dug in to the east of Wytschaete.On this day Brooke ordered a counterattack spearheaded by two battalions, the 3/Grenadier Guards and 2/North Staffordshire Regiment, both of Alexander’s 1^st Division. The North Staffords advanced as far as the Kortekeer river, while the Grenadiers reached the canal itself, but could not hold it. The counterattack disrupted the Germans, holding them back a little longer while the British Expeditionary Force continued its retreat.

The route back from Brooke’s position to Dunkirk passed through the town of Poperinge, where there was a bottleneck at a bridge over the Yser Canal, on which most of the area’s main roads converged. On 27 May, the Luftwaffe bombed the resulting jammed traffic for two hours, destroying or immobilising about four-fifths of the vehicles. Another Luftwaffe raid, on the night of 28/29 May, was illuminated by flares as well as the light from burning vehicles. The British 44^th Division in particular had to abandon many of its guns and lorries, losing almost all of them between Poperinge and the Mont.

Generalleutnant Werner Kempf’s 6^th Panzerdivision could probably have destroyed the 44^th Division at Poperinge on 29 May, which would also have cut off the 3^rd Division and 50^th Division, but Kempf was distracted, by the investment of the nearby town of Cassel.

Gort had ordered Adam and Général de Corps d’Armée Marie Bertrand Alfred Fagalde, commander of the British III Corps and French XVI Corps d’Armée respectively, to prepare a perimeter defence of Dunkirk. This was semi-circular in layout, with French troops manning the western sector and British troops the eastern. It ran along the Belgian coast from Nieuwpoort in the east via Veurne, Bulskamp and Bergues to Gravelines in the west. The line was made as strong as was possible under the circumstances. On 28 May the Belgian army fighting on the Lys river under the command of King Leopold III surrendered, and this left a 20-mile (32-km) gap in Gort’s eastern flank between the British and the sea. The British were surprised by the Belgian capitulation, despite Leopold’s earlier warning that he might have to do so. As a constitutional monarch, Leopold’s decision to surrender without consulting the Belgian government led to his condemnation by the Belgian and French prime ministers, Hubert Pierlot and Paul Reynaud. Gort sent the battle-worn 3^rd Division, 4^th Division and 50^th Division into the line to fill the gap left by the Belgian surrender. While these three formations were still moving into position, they ran headlong into Generalleutnant Gerhard Kauffmann’s 256^th Division, which were trying to outflank Gort. Armoured cars of the 12^th Royal Lancers stopped the Germans at Nieuwpoort itself. A confused battle raged all along the perimeter throughout 28 May. Command and control on the British side disintegrated, and the perimeter was driven slowly inwards toward Dunkirk.

Meanwhile, Generalmajor Erwin Rommel’s 7^th Panzerdivision had surrounded five divisions of the 1ère Armée near Lille. Although completely cut off and heavily outnumbered, the French fought for four days under the command of Général de Division Jean Baptiste Emmanuel Molinié in the 'Siege of Lille', thereby keeping seven German divisions from the assault on Dunkirk and saving an estimated 100,000 Allied troops. In recognition of the garrison’s stubborn defence, Oberst Dr Kurt Waeger, the LIII Corps' chief-of-staff, granted them the honours of war, saluting the French troops as they marched past in parade formation with rifles shouldered.

The defence of the Dunkirk perimeter held throughout 29/30 May, with the Allies falling back by degrees. On 31 May, the Germans nearly broke through at Nieuwpoort. The situation grew so desperate that two British battalion commanders manned a Bren gun, with one colonel firing and the other loading. A few hours later, the 2/Coldstream Guards of the 3^rd Division was rushed to reinforce the line near Furnes, where the British troops had been routed. The guardsmen restored order by shooting some of the fleeing troops and turning others around at bayonet point: the British troops returned to the line and the German assault was beaten back. In the afternoon, the Germans breached the perimeter near the canal at Bulskamp, but the boggy ground on the far side of the canal, but sporadic fire from the Durham Light Infantry halted them. As night fell, the Germans massed for another attack at Nieuwpoort, but 18 British bombers found the Germans as they were still assembling and scattered them with accurate bombing.

Also on 31 May, General Georg von Küchler, commander of the 18^th Army, assumed command of all the German forces at Dunkirk. His plan was simple: launch an all-out attack across the whole front at 11.00 on 1 June. Somewhat strangely, von Küchler ignored a radio intercept which revealed that the British were abandoning the eastern end of the line to fall back to Dunkirk itself. The morning of 1 June was clear, providing good flying conditions by contrast with the bad weather that had hindered air operations on 30 and 31 May: it is worth noting that there only 2.5 days of good flying conditions in the whole operation. Although Churchill had promised the French that the British would cover their escape, on the ground it was the French who held the line whilst the last remaining British soldiers were evacuated in the later stages of 'Dynamo'. Enduring concentrated German artillery fire and Luftwaffe strafing and bombing, the outnumbered French stood their ground. On 2 June, the day in which the last of the British units embarked, the French began to fall back slowly, and by 3 June the Germans were about 2 miles (3.2 km) from Dunkirk. The night of 3 June was the last night of evacuations. At 10.20 on 4 June, the German flag was hoisted over the docks from which so many British and French troops had escaped.

The resistance of Allied forces, especially those of France, including the French 12ème Division d’Infanterie Motorisée from the Fort des Dunes, had bought time for the evacuation of the bulk of the troops. The German took prisoner some 35,000 men, almost all of them French. These men had protected the evacuation until the last moment and were unable to embark. The same fate was reserved for the survivors of the 12ème Division d’Infanterie Motorisée (composed in particular of the 150ème Régiment), who were taken prisoner on the morning of 4 June on the beach of Malo les Bains after the regimental flag had been burned so as not to fall into German hands.

Following the events at Dunkirk, the German forces regrouped before starting 'Rot' (iii), their assault to the south, on on 5 June. Although some of the French soldiers who had been evacuated at Dunkirk returned to France a few hours later to attempt to halt the German advance and two fresh British divisions had begun moving to France in an attempt to create a 2^nd British Expeditionary Force, the decision was taken on 14 June to withdraw all the remaining British troops in 'Aerial', and by 25 June almost 192,000 Allied personnel, 144,000 of them British, had been evacuated through various French ports. Although the French army continued to fight, German troops entered Paris on 14 June and the French government was forced to negotiate an armistice signed at Compiègne on 22 June.

The loss of matériel on the beaches of Dunkirk was enormous. The British army abandoned enough equipment behind to fit out about eight to ten divisions. Discarded in France were, among other things, huge quantities of ammunition, 880 pieces of field artillery, 310 larger-calibre guns, some 500 anti-aircraft guns, about 850 anti-tank guns, 11,000 machine guns, nearly 700 tanks, 20,000 motorcycles and 45,000 motor cars and lorries. Army equipment available in the UK was sufficient only to equip two divisions. The British army needed months for proper re-equipment, and some planned introductions of new equipment were halted while industrial resources were concentrated on making good the losses. Officers told troops falling back from Dunkirk to burn or otherwise disable their trucks to prevent their use by the Germans. The shortage of army vehicles after Dunkirk was so severe that the Royal Army Service Corps was reduced to retrieving and refurbishing obsolete buses and coaches from British scrapyards for emergency use as troop transports.

It worth noting that after the completion of 'Dynamo', considerable numbers of British troops were still left in France in the area to the south of the Somme river. These numbered some 140,000 men, mostly logistic support and line of communication troops, but also including Major General V. M. Fortune’s 51^st Division and the remnants of the 1^st Armoured Division. On 2 June, Brooke was ordered back to France to supervise the creation of the 2^nd British Expeditionary Force, together with two further infantry divisions to follow, a project which Brooke believed was doomed to failure. After learning that most of the 51^st Division had surrendered after being cut off at St Valery en Caux on the English Channel coast, Brooke spoke to Churchill by telephone on 14 June and persuaded him to allow the evacuation of all the remaining British forces in France, and in 'Aerial' 144,171 British, 18,246 French, 24,352 Polish and 1,939 Czech troops were embarked for delivery to the UK in ships at several major ports along France’s western coast, along with much of their equipment. The last British troops left France on 25 June, the day France’s armistice with Germany came into force.