Operation Granit


'Granit' was the German airborne operation by part of Hauptmann Walter Koch’s Fallschirmjäger-Sturmabteilung 'Koch' of Generalleutnant Kurt Student’s 7th Fliegerdivision and Generalleutnant Hans Graf von Sponeck’s 22nd Luftlande-Division to seize and hold the fortress of Eben-Emael, a linchpin of the Belgian fixed defences, at the start of 'Sichelschnitt' (10/11 May 1940).

Together with 'Beton', 'Eisen' and 'Stahl' (iron, concrete and steel), this was one of a quartet of operations to take and hold key defensive positions which might otherwise have hindered the movement of the German forces into Belgium.

Although the German airborne arm had received its baptism of fire in 'Weserübung', albeit on only a small scale, it was in the course of the German campaign against Belgium and the Netherlands from 10 May 1940 that the whole concept of airborne operations was given its first major test, and it was for its part in this offensive that the main strength of the 7th Fliegerdivision and 22nd Luftlande-Division was reserved.

The overall 'Sichelschnitt' plan for a penetration through the Ardennes and then a drive to the coast of the English Channel, so dividing the Allied forces into two portions which could then be defeated separately, led to the allocation of an important role for the fledgling German airborne arm. As the definitive version of the German overall plan meant that only one Panzer division would be available for the attack on the central part of the Netherlands, and one for the drive through the Maastricht appendix in the southern part of the Netherlands during the advance into Belgium, the task of securing the vital water crossing points for these advances would be the primary responsibility of Student’s forces. While small detachments secured and held three bridges over the Albert Canal in Belgium, just over the border from Maastricht in the Netherlands, the bulk of the two divisions available to Student would attack the Hague and hold the bridges needed for the Panzer division moving up from the south to relieve the force.

The key to a successful crossing of the Albert Canal lay in the fortress of Eben-Emael, reckoned by the Belgians and the Allies to be the best modern fortress in the world. With excellent defensive positions and thick concrete walls, this fort commanded the three bridges the Germans would need in their drive to outflank the northern end of the French Maginot Line and the complex of Belgian forts around Liége. Running to the north-west from the fort at Eben-Emael were the bridges at Kanne, Vroenhofen and Veldwezelt. These three would have to be captured intact, and a coup-de-main party would have to take Eben-Emael to prevent its guns from destroying the bridges.

A plan of exceptional boldness and originality was therefore devised: while the 'Eisen', 'Beton' and 'Stahl' assault teams were flown in by glider to take the Kanne, Vroenhofen and Veldwezelt bridges respectively, the 'Granit' party would land in gliders right on top of the fortress and take the Belgian defenders, some 1,200 or more strong, from above in a surprise attack. Considering the importance of the attack, the forces allocated were small: Koch’s Fallschirmjäger-Sturmabteilung 'Koch'comprised only one company of Oberst Bruno Bräuer’s 1st Fallschirmjägerregiment and a parachute engineer platoon led by Leutnant Rudolf Witzig. The paratrooper company was split into three detachments for the task of taking the bridges, while Witzig’s engineers would land on and take Eben-Emael, which was rightly considered to be the crux of the defensive strength of the area. Aircraft allocations for the Fallschirmjäger-Sturmabteilung 'Koch' comprised 42 Junkers Ju 52/3m transport aircraft each towing one DFS 230 assault glider.

Early on the morning of 10 May the assault group lifted off in its gliders from Köln-Wahn and headed toward Maastricht. Surprise was of the essence, so the plan called for the Ju 52/3m aircraft to climb to an altitude of more than 8,200 ft (2500 m) over Germany, and release their gliders while still in German airspace. The gliders would then fly silently to their objectives.

This was the first time that such an operational tactic had been tried, and the men of the assault group had been undergoing intensive training since the previous November.

It was a cold night, and in the draughty gliders the men wrapped themselves tightly in blankets in their efforts to keep warm. At first the flight was uneventful, but then one of the tows broke and the glider came down in Germany: the glider was carrying Witzig and part of the engineer section, and this alone could have ruined the whole German plan. Such was the strength and efficiency of the training, and the initiative of the rest of the engineers, however, that the plan continued virtually without a hitch. One other glider was lost en route when its pilot released his tow too soon and failed to reach his objective. Two other gliders also failed to reach the bridges when their pilots came down at the wrong objectives. The rest of the glider force approached the target areas correctly and touched down close to the bridges, the paratroops pouring out as soon as they could, often before the glider had come to a complete halt.

Although some of the tug aircraft had crossed into Dutch airspace and been fired on by the Dutch anti-aircraft defences, this does not seem to have alerted the Belgian bridge garrisons. Even so, the Belgian defenders were not taken completely by surprise, and the paratroopers had to fight their way up to the bridges with small arms fire, flamethrowers and grenades. Once they had reached the bridges, the Germans were able to knock out the defending pillboxes with hollow charges. Each bridge was attacked by a detachment consisting of five paratrooper and four engineer sections, and the Germans moved in swiftly. Veldwezelt and Vroenhofen fell into German hands with little trouble, and the demolition charges were hastily but carefully removed.

Realising what was happening, the Belgian garrison at Veldwezelt had asked for permission to blow the bridge just as the Germans were taking it. The local Belgian headquarters, refusing to believe that German troops could have got on to the bridge without their knowing it, had refused to allow the demolition, and thus it fell intact into German hands.

At Kanne, however, the Belgians fared better. The German gliders had landed slightly too far away, and the defences were able to hold off the attackers just long enough to ask for permission to blow the bridge. Being the bridge farthest to the south, this was controlled by Eben-Emael’s commander, who realised the implications, especially as he knew of the fighting already taking place on the roof of his fortress, and so authorised the bridge garrison to blow their charge. Here alone, therefore, the Germans failed, principally because they had landed just too far away from their objective.

The key to the whole operation, though, was Eben-Emael itself, on whose roof nine of Witzig’s gliders landed in good order. The engineers stormed out, and immediately set about destroying the 12 gun emplacements which threatened them and the bridges. Next the six most important roof emplacements were blown open with large hollow charges, against which the Belgians had no defences. Killed or knocked unconscious by the blast of these charges, the Belgians could offer no resistance as the German engineers then blew their way into the emplacements and secured the top level of the fortress, effectively trapping the majority of the Belgian garrison in the rest of the fortress, from where it could do little damage.

Now completely in control of the situation unless the Belgians brought up massive reinforcements and heavy artillery, the Germans on the bridges and in the fortress waited for supplies, reinforcements of their own and the arrival of the relief forces. At 06.10 reinforcements and supplies arrived in the form of parachute drops of men, ammunition and other necessities for both the bridge garrisons and fortress group. Naturally enough, though, the Belgians were now fully alert, and caused the paratroops and their transport aircraft some casualties.

Having assessed the situation, the Belgians launched a number of counterattacks to try to retake the Vroenhofen and Veldwezelt bridges, but the paratrooper reinforcements received by the Germans included elements from the heavy machine gun company, whose weapons ensured the repulse of the counterattacks. The Kanne group, also reinforced, finally managed to fight its way on to the remnants of the bridge and drive off the Belgian garrison.

At 08.30 Witzig finally arrived to join the survivors of the 55 men who had made the original landing: after his glider had come down in Germany, he had called for another tug aircraft, which had landed in a field and managed to tow off the laden glider. Koch’s men now had to hold on until the conventional forces of Generaloberst Gerd von Rundstedt’s Heeresgruppe 'A' arrived. Firmly established in his headquarters near the Vroenhofen bridge, Koch was in radio contact with these forces, and knew that it should not be too long a time before relief arrived.

Yet the Belgians were counterattacking, and the German teams lacked heavy weapons. This situation was improved slightly after 10.15, when radio contact was made with a pair of 88-mm (3.465-in) batteries on the flanks of the advancing ground forces. These were able to provide some useful support fire. At 13.00 a forward artillery observer reached the most northerly bridge, and 90 minutes later the first ground forces, an infantry platoon, linked with the airborne soldiers. Koch was also in radio contact with the 51st Pionierbataillon, which was charged with the relief of Witzig’s men at Eben-Emael, and from this source knew that delays had been encountered. The battalion of Hauptmann Dr Theodor von Hippel’s Bau-Lehr-Bataillon 'Brandenburg' zbV 800 which that should have taken the bridges over the Maas river at Maastricht had failed to do so, and the Dutch had blown them. Nevertheless, Koch was informed by the 51st Pionierbataillon at Generalmajor Johann Stever’s 4th Panzerdivision and the 151st Regiment were making good progress across the Maastricht 'appendix' of the southern Netherlands.

Witzig’s men were now in the uncomfortable position of being shelled by Belgian artillery, but luckily for them no counterattack on Eben-Emael was launched. Cut off on the roof of the fortress, the German engineers were much relieved to see the leading elements of the 51st Pionierbataillon approaching Eben-Emael at 07.00 on 11 May. The battalion had fought its way across the Maas river and Albert Canal, and was soon joined by the 151st Regiment. The Germans outside the fortress launched a major attack on the main gates of the portion still held by the Belgians, who finally surrendered at 12.00.

By 16.00 Witzig’s men were able to pull out to rejoin the bridge parties, who had been relieved earlier, in Maastricht. The way was open for the 4th Panzerdivision to drive deep into the Allied defence line in Belgium. Only six of Witzig’s men had been killed and another 20 wounded, while the Belgian defenders of Eben-Emael had lost some 60 men killed, with the remaining 1,100 men effectively trapped and militarily impotent inside their own fortress.

The quartet of German airborne operations was just the tip of the operational iceberg in what became known as the Battle of Belgium or the 18 Days' Campaign in Belgium between 10 and 28 May 1940.

It was on 10 May that German forces invaded Belgium, Luxembourg and the Netherlands, all neutral countries, as the right wing of the 'Sichelschnitt' reworking of 'Gelb'. The Allied armies sought to halt the Germans in Belgium, believing this to be the primary German thrust. After the French had fully committed the best of the Allied formations to the Belgian front between 10 and 12 May, the Germans undertook the second but real primary phase of their assault by pushing through and past the hills and forests of the Ardennes region of southern Belgium to reach the Meuse river in north-eastern France in three locations (from north to south Dinant, Monthermé and Sedan), where the armoured forces of Generaloberst Herman Hoth’s XV Corps (mot.), General Hans-Georg Reinhardt’s XLI Corps (mot.) and General Heinz Guderian’s XIX Corps (mot.) broke through on 14/15 May and swept to the west and then to the north-west to reach the French coast of the English Channel from 20 May.

This trapped the Belgians, together with sizeable British and French forces, away from the rest of France.

In the period before the start of World War II, the Belgian strategy for a defence against German aggression had encountered major political as well military difficulties. In purely military terms, the Belgians did not wish to rely wholly on a linear defence of the Belgian/German frontier and thereby become what would in effect be a static northward extension of the French Maginot Line. This, the Belgians rightly appreciated, would leave them vulnerable to a German assault on their rear by means of an offensive through the Netherlands to fall on and break though the Belgian left flank. The strategy would also rely on the French to move quickly into Belgium and provide support, and the Belgians had a political distrust of the French.

Maréchal de France Philippe Pétain had suggested a French offensive directed at Germany’s key Ruhr industrial region, with Belgium as the springboard, in October 1930 and again in January 1933. This was one of several considerations which led Belgium to fear that it would be drawn into a war by powers greater than itself, and sought to avoid that eventuality. The Belgians also feared being drawn into a war as a result of the Franco/Soviet pact of May 1935. There was also a Franco/Belgian agreement whereby Belgium was to mobilise should Germany do so, but what remained clear was what was to happen in the event which actually triggered World War II, namely the German invasion of Poland in 'Weiss' (i).

Belgium preferred an alliance with the UK, for the latter was a known quantity as it had entered World War I in response to its treaty obligations when Germany violated Belgium’s neutrality. Once taken, Belgium’s English Channel ports had offered the Imperial German navy valuable bases for U-boats and light surfaces forces, and any repeat of successful German aggression in a new conflict would provide the German navy and, moreover, German air force with strategically and operationally important bases for the prosecution of offensive operations against the UK. The British government paid little attention to the concerns of the Belgians, however, and this lack of British commitment resulted in a Belgian withdrawal from the western alliance on 6 March 1936, the day before the German remilitarisation of the Rhineland.

The lack of British and French opposition to the remilitarisation persuaded the Belgians that the UK and France were not prepared to fight for their own strategic interests, and therefore would certainly not be wiling to fight for Belgium’s interests.

Thus Belgium decided not to rely on external support that might not be forthcoming, but instead to go it alone if this was required.

In October 1936 King Léopold III openly declared Belgium’s neutrality. This was a bitter blow to the French, whose army thus saw its strategic assumptions undermined: it could no longer look to close co-operation with the Belgians in defending the latter’s eastern borders, an eventuality which could have made it possible to check any German offensive well forward of the Franco/Belgian frontier, but rather look to whatever measure if co-operation it could persuade the Belgians to offer. The new situation deprived the French of the use of any prepared defences in Belgium to forestall an attack, a situation which the French had wanted to avoid as it meant engagement with the German armoured formations in a mobile battle. The French even considered an immediate invasion of Belgium should the Germans attack that country, not to aid in the defence of Belgium but to enlarge their own 'buffer zone' to the east of France’s north-eastern frontier.

Appreciating the danger posed by the revived militarism of the new Germany, Belgium secretly created its own defence policies, troop movement system, communications, fixed defensive dispositions, intelligence and air reconnaissance arrangements available to the French military attaché in Brussels.

The Allied plan to aid Belgium came down to a choice between the 'D-Plan' ('Dyle Plan') and the 'E-Plan' ('Escaut Plan'), in either of which the best of the Allied forces, Général d’Armée Gaston Henri Gustave Billotte’s 1er Groupe d’Armées would send the best of its formations to the north-east into western Belgium in the event of a German invasion.

When it came to the creation of an Allied line in Belgium, the choice lay between reinforcement of the Belgians in the east of the country along the Meuse-Albert Canal line parallel with but to the east of the Dyle river line in the 'D-Plan', or the retention of the estuary of the Scheldt (Escaut in French) river in the 'E-Plan' to link the French defences in the south with the Belgian forces protecting Ghent and Antwerp. Both had their military attractions, but also had the decided political weakness of abandoning most or much of eastern Belgium to the Germans in the 'D-Plan' and 'E-Plan' respectively. Général d’Armée Maurice Gustave Gamelin, the French commander-in-chief, saw possibilities in both plans, but opted for the 'D-Plan' as the core of France’s strategic defence.

Possessing no real field army and lagging in rearmament, the UK could do little to challenge the strategy adopted by the France, which had by default assumed the pre-eminent position in the western alliance. Having little in the way of ground forces with with to offer a strategic counterweight to the French, the British opted to make their major contribution in the air with a decision to undertake a strategic bombing campaign against the war-making industries of the Ruhr.

On their withdrawal from the western alliance, the Belgians refused to engage in any official meetings with the French or British military staffs for fear of compromising their neutrality. The Belgians did not regard a German invasion as inevitable, and were also sure that if an invasion did take place it would be effectively checked by Belgium’s new fortifications such as the great fortress of Eben-Emael commanding the junction of the Meuse river and Albert Canal. This and other new fortifications along the frontier with Germany reflected Belgium’s growing level of concern after the rise to power in January 1933 of Adolf Hitler and the Nazi party. The Belgian government had watched with increasing alarm the German withdrawal from the League of Nations, its repudiation of the Treaty of Versailles and its violation of the Locarno treaties. The Belgian government therefore spent very considerable sums on the modernisation of the fortifications at Namur and Liége, and the building of new defence lines along the Maastricht/Bois le Duc Canal linking the Meuse river, the Scheldt river and the Albert Canal. Protection of the eastern frontier was based mainly on the destruction of key roads in a task entrusted to new formations.

By 1935 the Belgian defences had been completed, but despite this there were now fears that the defences were no longer adequate. A major mobile reserve was needed to guard rear areas, and as a result it was considered that the protection against a sudden German assault was not sufficient. Large manpower reserves were also needed, but a bill for the provision of longer military service and army training was rejected by the public on the basis that it would increase Belgium’s military commitments and persuade the Allies to request Belgium to enter into conflicts far from home.

In a speech on 14 October 1936 in front of the council of ministers, the king tried to persuade the Belgian people and its government that stronger defences were necessary. Léopold III outlined three main military points for increased rearmament: firstly, that German rearmament, following upon the complete remilitarisation of Italy and the USSR had led most other states, even those that were deliberately pacifistic, such as the Netherlands, Sweden and Switzerland, to take exceptional precautions; secondly, that there has been so great a development in warfare, as a result of technical progress especially in aviation and mechanisation, that the initial operations of armed conflict could now be of such force and speed they were particularly alarming to small countries like Belgium; and thirdly, that Belgian anxieties have been increased by the lightning German reoccupation of the Rhineland and, with it, the creation of bases for the start of a possible German invasion moved considerably closer to the Belgian frontier.

On 24 April 1937, the French and British stated that the security of Belgium was of paramount importance to the western allies, who would defend their frontiers accordingly against any aggression, whether this aggression was directed solely at Belgium, or as a means of obtaining bases from which to wage war against 'other states'. Under these circumstances, France and the UK released Belgium from its Locarno treaty obligations to render mutual assistance in the event of German aggression toward Poland, while the UK and France nonetheless maintained their military obligations to Belgium.

Throughout this period the Belgian military operated on the basis of its belief that the German armed forces were stronger than those of the Allies, particularly the British army, and therefore that overtures to the western allies would result in Belgium becoming a battleground in a campaign in which the country lacked militarily adequate Allies. Moreover, the Belgians and French remained confused about what was expected of each other if or when hostilities began. The Belgians were determined to hold their border fortifications along the Albert Canal and the Meuse, without withdrawing, until French ground forces arrived to support them. Gamelin was not keen on pushing his 'D-Plan' that far, for he was concerned that the Belgians would be driven out of their fixed defences and would therefore retire to Antwerp, as they had in 1914. In fact the Belgian plan was for the divisions along the frontier with Germany to pull back and retire to the south to link with French forces. This information was not given to Gamelin.

As far as the Belgians were concerned, the 'D-Plan' had a number of advantages. Instead of the limited Allied advance to the Scheldt river, or meeting the Germans on the Franco-Belgian border, the move to the Dyle river line would reduce the length of the allied front in central Belgium by 43 miles (70 km), thereby freeing more forces for use as a strategic reserve. It was felt that the defence of the Dyle line would save more Belgian territory, in particular the eastern industrial regions. The 'D-Plan' also had the advantage of absorbing Belgian (and probably Dutch) formations including some 20 Belgian divisions.

On 10 January 1940 there took place the so-called 'Mechelen incident', in which Major Hellmuth Reinberger of the German army crash-landed in a Messerschmitt Bf 108 liaison aeroplane near Mechelen sur Meuse. Reinberger was carrying a copy of the 'Gelb' initial plan for a German invasion of western Europe which, as Gamelin had expected, was essentially a repeat of the 1914 Schlieffen plan and was thus centred on a German right-hook thrust through the Low Countries (including the Netherlands as well as Belgium) and into France. The Belgians suspected a ruse, but the plans were taken seriously. Belgian intelligence and the military attaché in the German city of Köln suggested the Germans would not actually launch an invasion based on this plan, and suggested instead that the Germans would try a left-hook punch through the Belgian Ardennes to reach Calais and thereby encircle the allied armies in Belgium. The Belgians had correctly predicted what Generalleutnant Erich von Manstein now developed in 'Sichelschnitt'.

The Belgian high command warned its French and British counterparts of its concerns, and pointed out that the implementation of the 'D-Plan' would, in these circumstances, would jeopardise not only the Belgian strategic position but also the entire left wing of the allied front. Léopold III and his aide de camp, Lieutenant General Raoul Van Overstraeten, warned Gamelin and the French army high command of their concerns on 8 March and 14 April, but their warnings were not heeded.

The Belgian plan in the event of German aggression provided for a delaying position along the Albert Canal from Antwerp to Liége and the Meuse river from Liége to Namur, which was to be held long enough to allow French and British troops to occupy the line linking Antwerp and Givet via Namur by the third day of the invasion; withdrawal to the Antwerp/Namur position; and the Belgian army’s retention of the sector (excluding Leuven [Louvain] but including Antwerp) as part of the main allied defensive position.

In an agreement with the British and French, the former’s British Expeditionary Force under the command of General the Lord Gort was to occupy the central position in the Brussels/Ghent gap supporting the Belgian army holding the main defensive positions some 12.5 miles (20 km) to the east of Brussels, while the latter’s 7ème Armée under the command of Général d’Armée Henri Honoré Giraud was to advance into Belgium, past the Scheldt river estuary in Zeeland if possible, to reach Breda in the Netherlands. The main defensive perimeter round the great port city of Antwerp would be protected by the Belgians, barely 6.2 miles (10 km) from the city. In the Breda area, the French 7ème Armée would be in a position to protect the left flank of the Belgian army formations protecting Antwerp, and to threaten the German northern flank.

Farther to the east, delaying positions were constructed in the tactical zones along the Albert Canal, which joined with the defences of the Meuse to the west of Maastricht. The line then deviated to the south and continued to Liége. The gap between Maastricht and Liége was strongly protected: the Eben-Emael fortress guarded the city’s northern flank, the 'tank country' in the strategic depths of the Belgian forces occupying the city, and the axis of advance into the west of the country. More defence lines extended to the south-west, covering the Liége/Namur axis. The Belgian army also had the benefit of the advance of Général d’Armée Georges Maurice Jean Blanchard’s French 1ère Armée toward Gembloux and Hannut, on the southern flank of the British Expeditionary Force and covering the Sambre river sector. This shielded the gap in the Belgian defences between the main positions on the Dyle line and Namur to the south. Still farther to the south, Général d’Armée André Georges Corap’s French 9ème Armée advanced to the Givet/Dinat axis on the Meuse river. Général d’Armée Charles Léon Clément Huntziger’s French 2ème Armée was responsible for the last 60 miles (100 km) of the front in positions covering Sedan, the lower part of the Meuse river, the Belgian/Luxembourg border, and the northern end of the Maginot Line.

The German plan called for Generaloberst Fedor von Bock’s Heeresgruppe 'B' to advance into the Netherlands and north-eastern Belgium, and thus to draw Billotte’s 1er Groupe d’Armée into central Belgium, while Generaloberst Gerd von Rundstedt’s Heeresgruppe 'A' launched its surprise advance through the Ardennes.

Within 'Sichelschnitt', Belgium and the Netherlands were secondary objectives, so von Bock’s Heeresgruppe 'B' had only two armies and three armoured and mobile formations (including General Erich Hoepner’s XVI Corps [mot.]) within its total of 29.5 divisions, whereas Heeresgruppe 'A' had three armies with 45.5 divisions including seven armoured and three motorised divisions. After Heeresgruppe 'B' had achieved most of its tasks, its Panzer divisions and most of its motorised infantry divisions were to be reallocated to strengthen Heeresgruppe 'A''s lines of communication and to prevent an Allied break-out. However, this would be impossible if Heeresgruppe 'B' failed to take the required territory sufficiently rapidly and so squeeze the Allied forces on two fronts.

The key to the task of slowing the Germans, so the Belgians believed, was the defensive hub constituted by the fortress of Eben-Emael and the Albert Canal, for it was clear that any rapid advance by Heeresgruppe 'B' was dependent on the Germans' swift seizure and then their retention of the three bridges over the canal at Veldwezelt, Vroenhoven and Kanne in Belgium, and also Maastricht on the Dutch border. The failure to take and hold the bridges would leave Generaloberst Walter von Reichenau’s 6th Army, the southern element of Heeresgruppe 'B', trapped in the Maastricht/Albert Canal enclave and subject to the guns of the Eben-Emael fortress. Thus this fort had to be captured or destroyed.

Hitler summoned Generalleutnant Kurt Student, commander of the 7th Fliegerdivision, to discuss the assault. It was first suggested that a conventional parachute drop be made by airborne forces to seize and destroy the fortress’s artillery before any land units approached. Such a suggestion was rejected as the Junkers Ju 52/3m transport aircraft were too slow and likely to be vulnerable to Dutch and Belgian anti-aircraft fire. Other factors for its refusal were the weather conditions, which might blow the paratroopers away from the fort and disperse them too widely: the seven-second drop from a Ju 52/3m at minimum operational height was reckoned to result in a dispersion of more than 330 yards (300 m).

Hitler had noticed one potential flaw in the defences: the roofs were flat and unprotected. He now demanded to know if a glider, such as the DFS 230, could land on them. Student replied that it could be done, but only by 12 aircraft and in daylight; this would deliver a force of 80 to 90 paratroopers onto the target. Hitler then revealed the tactical weapon that would make this strategic operation work, introducing the Hohlladungwaffe (hollow-charge weapon), which was a 110-lb (50-kg) device which would destroy the Belgian gun emplacements. It was this tactical unit that would spearhead the first strategic airborne operation in history.

In May 1940 the Belgian army could deploy 22 divisions with 1,338 pieces of artillery pieces but only 10 French-built Renault AMC-35 cavalry tanks. However, the Belgian combat vehicle fleet also included included 200 T-13 tank destroyers each fitted with an excellent 47-mm anti-tank gun as well as a 0.3-in (7.62-mm) FN30 co-axial machine gun in a traversing turret. The Belgians also possessed 42 T-15 vehicles that were notionally armoured cars but actually fully tracked tanks with a 13.2-mm (0.52-in) turret machine gun. The standard Belgian anti-tank gun was the 47-mm FRC, towed either by trucks or by fully tracked armoured Utilitie B tractors. One report states that a round from a 47-mm gun went straight through a SdKfz 231 armoured car and penetrated the armour of a PzKpfw IV battle tank behind it. These Belgian guns were better than the 25-mm and 37-mm anti-tank guns used by the French and Germans respectively.

Belgium started its mobilisation on 25 August 1939, and by May 1940 could call on a field army of 18 infantry divisions, two divisions of Chasseurs Ardennais (partly motorised) and two motorised cavalry divisions, a force totalling some 600,000 men. The Belgian reserves may have been able to field 900,000 men. However, the Belgian army lacked useful numbers of armoured vehicles and anti-aircraft guns. After the completion of its mobilisation, the Belgian army had five regular corps and two reserve corps in the form of the I Corps (1st, 4th and 7th Divisions), II Corps (6th, 11th and 14th Divisions), III Corps (1st Chasseurs Ardennais Division, and 2nd and 3rd Divisions), IV Corps (9th, 15th and 18th Divisions), V Corps (12th, 13th and 17th Divisions), VI Corps (5th, 10th and 16th Divisions), VII Corps (8th Division and 2nd Chasseurs Ardennais Division), Cavalry Corps (1st and 2nd Cavalry Divisions), and a brigade of motorised cavalry. Thus the Belgians had 12 regular infantry divisions, two Chasseurs Ardennais divisions and six reserve infantry divisions, together with a brigade of Cyclist Frontier Guards. There were also two anti-aircraft artillery and four artillery regiments and a now-unknown quantity of fortress, engineer and signals force personnel.

The Belgian Naval Corps was resurrected in 1939, and most of the Belgian merchant fleet, of some 100 ships, evaded capture by the Germans. Under the terms of a Belgian and British agreement these ships, together with 3,350 men, were placed under British control for the duration of the war. The Belgian naval headquarters was located at Ostend under the command of Major Henry Decarpentrie, with the 1st Naval Division also based at Ostend and the 2nd and 3rd Naval Divisions at Zeebrugge and Antwerp respectively.

The Aéronautique Militaire Belge had barely begun to modernise its aircraft inventory. It had ordered Brewster Buffalo, Fiat CR.42, Hawker Hurricane and Koolhoven F.K.56 fighters, Fairey Battle and Caproni Ca.312 light bombers, and Caproni Ca.335 reconnaissance fighters. Only the CR.42, Hurricane and Battle aircraft had been delivered, and the shortage of modern types was reflected in the fact that a single-seat version of the Fairey Fox light bomber was used as a fighter.The Belgian air arm had 250 combat aircraft including at least 90 fighters, 12 bombers and 12 reconnaissance aircraft, bit only 50 of these machines were of reasonably modern standard. With liaison and transport aircraft from all services added, the Belgians had 377 aircraft, but of these only 118 (78 fighters and 40 bombers) were serviceable on 10 May 1940.

The air arm had been commanded since 1938 by Major General Paul Gustave Lambert Joseph Hiernaux, who had organised the service into three air regiments: the 1ère Régiment d’Aéronautique with 60 aircraft, the 2ème Régiment d’Aéronautique with 53 aircraft, and the 3ème Régiment d’Aéronautique with 79 aircraft.

The Belgians were afforded substantial support by the French in the form of the 1ère Armée, which included Général de Corps d’Armée René Jacques Adolphe Prioux’s Corps de Cavalerie including the 2ème and 3ème Divisions Légères Mécaniques (2nd and 3rd Light Mechanised Divisions) allocated to defend the Gembloux gap. This armoured strength was based on 176 formidable SOMUA S-35 cavalry tanks and 239 Hotchkiss H-35 light tanks which were both superior to German tanks in armour and firepower. The stronger of the two French divisions was the 3ème DLM, which had 90 S-35 and some 140 H-35 machines.

The French 7ème Armée assigned to protect the northernmost part of the Allied front, and included the 3ème DLM and two motorised divisions (the 9th and 25th). This force was to advance to Breda in the Netherlands.

The third French army to see action on Belgian soil was the 9ème Armée, which was weaker than both the 7ème Armée and 1ème Armée. The 9ème Armée had only infantry divisions, with the exception of the 5ème Division Motorisé, and its task was the protection of the southern flank of the Allied armies, to the south of the Sambre river and just to the north of Sedan. Farther to the south, in France, was the French 2ème Armée, protecting the Franco-Belgian border between Sedan and Montmédy. Thus the two weakest French armies were protecting the area through which the Germans planned to deliver their main 'Sichelschnitt' thrust.

The British contributed the weakest of the Allied forces in Belgium, for the British Expeditionary Force had just 152,000 men in two corps each of two divisions, though it had been hoped to field two armies of two corps each in a mobilisation that could not be completed. The I Corps was commanded by Lieutenant General Sir John Dill, later Lieutenant General M. G. H. Barker and then Major General the Hon. Sir Harold Alexander. The II Corps was commanded by Lieutenant General Sir Alan Brooke. Later the III Corps, commanded by Lieutenant General Sir Ronald Adam, was added to the British order of battle. Air support was the task of the 9,392 men of the Royal Air Force’s Advanced Air Striking Force under the command of Air Vice Marshal P. H. L. Playfair.

By May 1940 the BEF had grown to 394,165 men, of whom more than 150,000 were part of the logistical rear area organisations and had little military training. On 10 May 1940, the BEF comprised just 10 divisions (not all of them at full strength), 1,280 pieces of artillery and 310 tanks.

On the other side of the front line, von Bock’s Heeresgruppe 'B' had 26 infantry and three Panzer divisions for the invasion of the Netherlands and Belgium. Of the three Panzer divisions, Generalmajor Horst Stumpff’s 3rd Panzerdivision and Stever’s 4th Panzerdivision were to operate in Belgium under the command of the 6th Army's XVI Corps (mot.). Generalleutnant Alfred Ritter von Hubicki’s 9th Panzerdivision was attached to General Georg von Küchler’s 18th Army which, after the Battle of the Netherlands, was to support the push into Belgium alongside the 6th Army and cover its northern flank.

The armoured strength of Heeresgruppe 'B' was 808 tanks, of which 282 were PzKpfw I and 288 PzKpfw II light tanks, 123 PzKpfw III medium tanks and 66 PzKpfw IV battle tanks; there were also 49 command tanks. The 3rd Panzerdivision's armoured regiments had 117 PzKpfw I, 128 PzKpfw II, 42 PzKpfw III, 26 PzKpfw IV and 27 command tanks. The 4th Panzerdivision's armoured regiments had 136 PzKpfw I, 105 PzKpfw II, 40 PzKpfw III, 24 PzKpfw IV and 10 command tanks. The 9th Panzerdivision, scheduled initially for operations in the Netherlands, was the weakest of the three armoured formations as its regiments had only 30 PzKpfw I, 54 PzKpfw II, 66 PzKpfw III and 49 PzKpfw IV machines.

The elements drawn from Student’s 7th Fliegerdivision and on Sponeck’s 22nd Luftlande-Division for the 'Granit' attack on Eben-Emael constituted Koch’s Fallschirmjäger-Sturmabteilung 'Koch'. Assembled in November 1939, this special force comprised primarily paratroopers of the 1st Fallschirmjägerregiment and engineers of the 7th Fliegerdivision, as well as a small group of Luftwaffe pilots.

The Luftwaffe allocated 1,815 warplanes, 487 transport aircraft and 50 gliders for the assault on the Low Countries. The first attacks on Belgium were undertaken by General Alfred Keller’s Düsseldorf-headquartered IV Fliegerkorps, of Generaloberst Albert Kesselring’s Luftflotte II, using the Stab, I, II, III and IV/Lehrgeschwader 1, the Stab, I, II and III/Kampfgeschwader 30, and the III/KG 27. For his tasks on 10 May Keller had 363 aircraft, of which 224 were serviceable, supplemented by Generalmajor Wolfram von Richthofen’s VIII Fliegerkorps with 550 aircraft, of which 420 were serviceable. Fighter support was provided by Generalmajor Kurt-Bertram von Döring’s Jagdfliegerführer 2 command, which had 462 fighters of which 313 were serviceable. The German aircraft operated from Oldenburg, Marx, Grevenbroich, Mönchengladbach, Dortmund and Essen, among other bases.

During the evening of 9 May, the Belgian military attaché in Berlin suggested to his superiors that the Germans intended to invade Belgium on the next day. There were other indications of the German intention, and Belgium instigated a full state of alert at 01.30 on 10 May, after which the Belgian forces took up their deployment positions and the king moved to his headquarters near Briedgen in the Antwerp area. The Allied armies also started to implement the 'D-Plan' on the same day, and were already moving up toward the rear of the Belgian positions.

As in all of the Blitzkrieg offensives, the German spearhead was the Luftwaffe, whose first task was the elimination of the Belgian air arm. Despite their overwhelming numerical strength, with 1,375 aircraft of which 957 were serviceable, the Germans gained only limited success over Belgium on the first day. At about 04.00 the Germans made their first air raids on Belgian airfields and communication centres, and gained superiority over the Belgian air arm’s 179 serviceable aircraft. The most effective of the German air formations was the VIII Fliegerkorps, and especially its KG 77 commanded by Oberst Dr Johann-Volkmar Fisser, which co-operated with Oberst Walter Lachner’s KG 54 in the destruction of the Belgian air arm’s main bases. Fighters of Oberstleutnant Max Ibel’s Jagdgeschwader 27 destroyed two Belgian squadrons at Neerhespen, and during the afternoon the dive-bombers of Hauptmann Hubertus Hitschold’s I/Stukagescheswader 2 destroyed nine of the 15 CR.42 fighters at Brusthem. At Schaffen-Diest, three Hurricane fighters of Escadrille 2/I/2 were destroyed and another six damaged when a wave of Heinkel He 111 medium bombers caught them as they were about to take off; another two were lost when their hangars were destroyed hangars. At Nivelles 13 CR.42 fighters were destroyed, and at Belesle the bombers of Oberst Hans Behrendt’s KG 27 destroyed eight aircraft.

The fighting between German aircraft and the Belgian aircraft which did manage to get into the air was equally one-sided in favour of the Germans. Although the Belgian Gloster Gladiator and Hurricane fighters managed to shoot down two He 111 and two Dornier Do 17 bombers as well as three Messerschmitt Bf 109 fighters, the fighters of JG 1, 21 and 27 downed eight Gladiator, five Fairey Fox and one CR.42 aircraft. The RAF’s No. 18 Squadron despatched two Bristol Blenheim light bombers on operations over the Belgian front, but lost both to Bf 109 fighters.

By the end of 10 May, the official German figures indicate claims for 30 Belgian aircraft destroyed on the ground and 16 (including the two RAF bombers) in the air for 10 losses. The victory claims are in all probability under the actual count, for 83 Belgian machines (most of them trainers and 'hacks') were destroyed. The Belgian air arm flew only 146 sorties in the first six days of the campaign, and then just 77 between 16 May and the Belgian surrender on 28 May.

As noted above, the German planners had recognised some time before the launch of 'Sichelschnitt' that the key to a swift penetration into the interior of Belgium was the fortress of Eben-Emael, and this was taken in 'Granit'. With the main Belgian defence positions thus breached, the infantry formations of the 6th Army poured through the gap. The Germans had also established bridgeheads across the Albert Canal some two days later, before the British were able to reach it. Farther to the south, the Chasseurs Ardennais withdrew behind the Meuse, destroying some of the river bridges as they retired.

More successful German airborne operations took place in Luxembourg, where five crossings and communication routes leading into France were seized. Carried out by 125 volunteers of Generalleutnant Hans Behlendorff’s (from 11 May Generalleutnant Friedrich Fürst’s) 34th Division, the 'Hedderich' operation was centred on the use of Fieseler Fi 156 Storch light aircraft to deliver the assault teams, who were led by Leutnant Wenner Hedderich. The cost to the Germans was five aircraft and 30 men killed.

With Eben-Emael lost, the Belgian 4th and 7th Divisions were confronted by the prospect of combat on terrain which favoured the attackers' armour. The 7th Division, with its 2nd and 18th Grenadier Regiments and the 2nd Carabineers, struggled to hold its positions and contain the German infantry on the west bank, and Belgian tactical units in fact launched several counterattacks. At one point, at Briedgen, the Belgians succeeded in retaking the bridge and then blowing it. At the other points, notably Vroenhoven and Veldwezelt, in 'Beton' and 'Stahl' the Germans had had time to seize the bridges and establish strong bridgeheads, and therefore to repulsed the Belgian counterattacks.

Another airborne operation was 'Niwi' also undertaken on 10 May in southern Belgium. The objectives of this operation was to land two companies of the 3/Infanterieregiment 'Grossdeutschland' by Fi 156 light aircraft at Nives and Witry to clear a path for Generalleutnant Friedrich Kirchner’s 1st Panzerdivision and Generalleutnant Rudolf Veiel’s 2nd Panzerdivision of Guderian’s XIX Corps (mot.), which were advancing through the Ardennes in the area of the Belgian and Luxembourgois border. The original plan had called for the use of Ju 52/3m transport aircraft, but the short landing capability of the Fi 156 led to the use instead of 200 of these aircraft in an assault tasked with the cutting of signal communications and message links on the roads linking Neufchâteau and Bastogne and Neufchâteau and Martelange, the prevention of the approach of Belgian reserves from the Neufchâteau area, and the facilitation of the advance by exerting pressure against the line of pillboxes along the border from the rear.

The German infantry was engaged by several Belgian patrols equipped with T-15 armoured cars, but beat off several Belgian counterattacks, among them an effort by the 1st Light Ardennes Division. Unsupported, the Germans faced a counterattack later in the evening by elements of the French 5ème Division de Cavalerie, dispatched by Huntziger of the French 2ème Armée, which had considerable armoured strength and compelled the surviving Germans to retreat. The French failed to launch any pursuit, however, and halted at a dummy barrier that the Germans had erected as they fell back. By the next morning, however, the 2nd Panzerdivision reached the area and the mission had largely been accomplished.

But from the German perspective, the operation actually hindered rather than helped Guderian’s corps. 'Niwi' had blocked the roads and, against the odds, prevented French reinforcements reaching the area in which the Belgian, French and Luxembourgois frontiers met, but also destroyed Belgian telephone communications and thus inadvertently prevented Belgian commanders from recalling the units along the border. The Belgian 1st Light Division did not receive the signal to retreat and therefore engaged in a severe firefight with the German armour, whose advance was therefore slowed.

The failure of the French and Belgian forces to hold the Ardennes gap was a mistake that was fatal to the survival of Belgium and, indeed, France. At the time of the German invasion the Belgians had withdrawn laterally, in the process demolishing and blocking routes of advance: this delayed the French 2ème Armée’s movement to the north in the direction of Namur and Huy, and German assault engineers had been able to clear the obstacles without armed challenge. The delay that the Belgians' high-quality Ardennes Light Infantry could have inflicted on the advancing German armour was proved by the fight for Bodange, where the 1st Panzerdivision was checked for eight hours.

In their central sector, meanwhile, after failing to restore their front by ground attack the Belgians attempted on 11 May to bomb the bridges and positions that the Germans had captured intact and were now holding. But a squadron which attempted to do so lost 11 out of 12 aircraft during one such mission. The German operations against what was left of the Belgian air arm were spearheaded by Major Hans-Hugo Witt’s JG 26, which made 82 of the German claims in aerial combat between 11 and 13 May. Despite the apparent success of the German fighter units, the air battle was not entirely one-sided: during the morning of 11 May 10 of StG 2's Ju 87 dive-bombers were shot down while attacking Belgian forces in the Namur-Dinant gap, despite the presence of fighters of JG 27 and Oberstleutnant Theo Osterkamp’s JG 51. Even so, the Germans noted a weakening of Allied air resistance in northern Belgium by 13 May.

During the night of 11/12 May, Major General B. L. Montgomery’s British 3rd Division reached its position on the Dyle river at Leuven. As it did so, the Belgian 10th Division, occupying the position, mistook the the British soldiers for German paratroopers and fired on them. The Belgians refused to yield, but Montgomery claimed to have got his way by placing himself under local Belgian command in the knowledge that when the Germans came within artillery range the Belgians would withdraw.

Commanding the British II Corps, Brooke tried to sort out the matter of co-operation with the Belgian king, and it seemed that a compromise could be reached. Van Overstraeten, the king’s aide de camp, intervened to say that the 10th Division could not be moved and that the British division should move farther to the south and remain completely clear of Brussels. Brooke told the king that the 10th Division was on the wrong side of the line agreed with Gamelin and therefore exposed. Léopold III deferred to his adviser, despite the fact that Brooke had found Van Overstraeten to be ignorant both of the situation and of the BEF’s dispositions. Given that the BEF’s left flank rested on its Belgian ally, the British were now unsure about Belgian military capabilities and determination. The Allies had more serious grounds for complaint about the Belgian anti-tank defences along the line of the Dyle river covering the Namur/Perwez gap, where there were no natural obstacles. Only a few days before the attack had it been learned that the Belgians had sited their anti-tank defences several miles to the east of the Dyle between Namur and Perwez.

After holding the Albert Canal’s western bank for nearly 36 hours, the 4th and 7th Divisions withdrew. The capture of Eben-Emael allowed the Germans to force through the 6ème Armée’s tank dispositions. The Belgian divisions were now faced with the situation in which they had to withdraw or be encircled. The Germans had driven forward beyond Tongres, and were now in a position to sweep south to Namur, which threatened the envelopment of the entire Albert Canal and Liége positions. Under these circumstances both divisions withdrew. On the evening of 11 May, the Belgian high command withdrew its forces behind the Namur/Antwerp line. On the following day the French 1ère Armée reached Gembloux, between Wavre and Namur, to cover the so-called 'Gembloux gap', which was a flat area, devoid of prepared positions.

The French 7ème Armée, on the northern flank of the Belgian line, protected the Bruges/Ghent/Ostend axis and, covering the Channel ports, had advanced into Belgium and thence into the Netherlands with all speed. The army’s leading elements reached Breda in the south-western part of the Netherlands on 11 May. But by this time German airborne forces had seized the Moerdijk bridge on the Hollands Diep river, to the south of Rotterdam, making it impossible for the French to link with the Dutch. The Dutch then pulled back to the north in the direction of Rotterdam and Amsterdam. The French 7ème Armée turned to the east and met the 9th Panzerdivision about 12.5 miles (20 km) to the east of Breda at Tilburg. The battle that followed compelled the French to retire, under German air attack, toward Antwerp, where it later became involved in the defence of this great port city.

The Luftwaffe had given priority to attacking the French 7ème Armée’s leading elements as they moved into the Netherlands as this advance threatened the Moerdijk bridgehead. The level bombers of Lackner’s KG 54, supported by Ju 87 dive-bombers of the VIII Fliegerkorps, helped drive back the French. Concerns that the Allies might try to deliver reinforcements to Belgium by sea through Antwerp persuaded the Germans to make a major effort over the estuary of the Scheldt river, and here estuary, and here the level bombers of Oberleutnant Walter Loebel’s KG 30 attacked and sank two Dutch gunboats and three Dutch destroyers, as well as badly damaging two British destroyers. In overall terms, however, the German bombing had only limited effects.

During the night of 11/12 May, the Belgians were fully engaged in their withdrawal to the Dyle river line, covered by a network of demolitions and rearguards astride Tongres. During the morning of 12 May, the king, Van Overstraeten, Édouard Daladier (ex-prime minister of France and currently minister of defence), Général d’Armée Alphonse Georges (commander of the Allied North-East Front centred on the 1er Groupe d’Armées and comprising the BEF and the French 1ère, 2ème, 7ème and 9ème Armées), Billotte (commander of the 1er Groupe d’Armées and co-ordinator of the Allied Armies) and Lieutenant General Sir Henry Pownall (Gort’s chief-of-staff) met near Mons, and agreed that the Belgian army would control the line between Antwerp and Leuven line, while the French and British took responsibility for the extreme north and south of the country.

The Belgian III Corps (1st Chasseurs Ardennais, and 2nd and 3rd Divisions) had pulled back from the defences of Liége to avoid encirclement, though the Liége Fortress Regiment remained to disrupt German communications. Farther to the south, in the fortifications of Namur the Belgian VI Corps' 5th Division and the 2nd Chasseurs Ardennais Division, supplemented by the French 12ème Division, fought delaying actions and undertook a mass of demolitions.

The Belgians believed that they had accomplished the only independent mission assigned to their army, namely to hold the Liége/Albert Canal line for a period long enough to allow Allied formations to come to the support of the other Belgian forces occupying the line connecting Namur, Antwerp and Givet. For the rest of the campaign, the Belgians fought within the context of an overall Allied plan.

Belgian units now fought rearguard actions while other Belgian units already on the Dyle river line worked to improve the defensive positions in the gap between Leuven and Antwerp. The 2nd Regiment of Guides and the 2nd Carabineers Cyclists of the 2nd Cavalry Division covered the retreat of the Belgian 4th and 7th Divisions, and performed well in the battles at Tirlemont and Haelen.

The Belgian forces' failure to hold their eastern frontiers where, it had been believed, they could hold out for two weeks, was a major disappointment for the Allies. The Allied high command had attempted to avoid a mobile battle without any strong fixed defences on which to retire if necessary, and had hoped Belgian resistance would last long enough for the establishment of a firm defensive line. Nevertheless, a brief lull had fallen on the Dyle river front on 11 May, and this had provided the opportunity for the Allied armies to get into position by the time the Germans launched their first major assault on the following day. Allied cavalry had moved into position, but much of the infantry and artillery were reaching the front more slowly by rail. Although unaware of it, the Allied 1er Groupe d’Armées and the Belgian army in fact outnumbered and outgunned von Reichenau’s 6th Army.

On the morning of 12 May the RAF and Armée de l’Air responded to Belgian pressure and, in fact, a very real military necessity, with air aids on the German-held bridges at Maastricht in the southern Netherlands and along other stretches of the Meuse river in an effort to prevent the advance of the German forces into Belgium. Here the Allied air forces had flown 74 sorties since 10 May, but on 12 May, 11 out of 18 French Breguet Bre.693 bombers were shot down, and the RAF’s Advanced Air Striking Force was reduced to 72 aircraft out of 135 through losses to its Battle light bomber forces in vain attacks on these bridges. Missions were postponed on 13 May as the German anti-aircraft and fighter defences had been proved to be too strong for the survival of Allied bombers in all but the tiniest numbers.

Although the German ground forces believed that they had received less fighter cover than they needed, he fact remains that the Allies had been able to provide considerably less than adequate protection to their bombers: in all, 45 out of 109 Battle and Blenheim light bombers which attacked German columns and communications in the Sedan area had been lost. On 15 May, the Allied daylight bombing effort was scaled back: of the 23 aircraft despatched, four failed to return. It was not all one-way traffic, however, for Guderian’s XIX Corps (mot.) noted that the corps no longer had its own long-range reconnaissance capability as the relevant squadrons were no longer in a position to provide extensive, deep reconnaissance as more than half of their aircraft had been lost.

The most serious fighting on 12 May 1940 was the day of the Battle of Hannut (12/14 May), in which the French under Prioux committed two armoured divisions (20,800 men and 600 armoured fighting vehicles) and the Germans under Hoepner two Panzer divisions (25,925 men, 618 or, according to some sources, 674 armoured fighting vehicles, 108 pieces of artillery and 1,252 aircraft). Even as Heeresgruppe 'A' advanced through the Belgian Ardennes, the 6th Army of Heeresgruppe 'B' launched an offensive toward the Gembloux gap. Lying on the Belgian plain, Gembloux was the centre of an unfortified area in the main Belgian defensive line, the eponymous gap extending from the southern end of the Dyle line, between Wavre in the north and Namur in the south, over a distance of 12,5 miles (20 km). After attacking out of the Maastricht 'appendix' of the southern Netherlands and defeating the Belgian defences at Liége, thereby compelling the Belgian I Corps to retreat, the 6th Army's XVI Corps (mot.), under Hoepner’s command and including Stumpff’s 3rd Panzerdivision and Stever’s 4th Panzerdivision, launched an attack in the area where the French mistakenly expected the main German thrust.

The Gembloux gap was held by the French 1ère Armée, with six elite divisions including the two light mechanised divisions of Prioux’s Corps de Cavalerie, which were to advance 18.5 miles (30 km) to the east of the Allied line to provide a screen as heavier armoured forces moved behind the French French 1ère Armée to defend the main line in depth. In overall strength the Cavalry Corps was equal to a German Panzer corps, and was to occupy a screening line on the Tirlemont/Hannut/Huy axis. The operational plan called for the Cavalry Corps to delay the German advance on Gembloux and Hannut until the main elements of the French French 1ère Armée had reached Gembloux and dug in.

Hoepner’s and Prioux’s corps met head-on near Hannut on 12 May. The 3rd Panzerdivision and 4th Panzerdivision had 280 and 343 tanks respectively, while the 2ème and 3ème DMLs included 176 Somua S-35 cavalry and 239 Hotchkiss H-35 light tanks, and added to this armoured force were a considerable number of Renault AMR-35ZT-63 light infantry tanks in the Cavalry Corps. The R-35 was equal or superior to the PzKpfw I and II light tanks in armament terms, and so too were the 90 Panhard 178 armoured cars of the French army. In terms of tanks that were capable of engaging successfully in a tank-versus-tank engagement, the Germans possessed just 73 PzKpfw III medium tanks and 52 PzKpfw IV battle tanks.

However, the German forces were able to communicate by radio during the battle, and could therefore shift the focus of their main effort unexpectedly, and they had also practiced combined arms tactics, while the French tactical deployment was a rigid descendant of the tactics of World War I. Moreover, French tanks did not possess radio and commanders often had to dismount to issue their orders. Despite their notional disadvantages in armament, the Germans managed to gain the upper hand in the morning battle on 12 May, encircling several French battalions. Then the combat power of the 2ème DLM managed to defeat the German forces encircling the pockets and free the trapped units. In overall terms, though, the French emerged tactically victorious on the first day, preventing a German breakthrough to Gembloux or seizure of Hannut.

On the following day, 13 May, the French were undone by their poor tactical capabilities. They extended their armour in a thin line between Hannut and Huy, providing no defence in depth, which had been the point of sending the French armour to the Gembloux gap in the first place. This left Hoepner with a chance to mass the German armoured strength against the 3ème DLM and achieve a breakthrough. Moreover, with no reserves behind the front, the French had denied themselves the opportunity to mount any counterattack after the XVI Corps (mot.) had outmanoeuvred the 2e DLM on its left flank. The Belgian III Corps, retreating from Liége, offered to support the French front still held by the 3e DLM, but the offer was rejected.

On 12 and 13 May, the 2e DLM had lost no armoured fighting vehicles, while the 3e DLM had lost 30 S-35 and 75 H-35 machines; another 16 miscellaneous French armoured fighting vehicles were knocked out. The French had disabled 160 German tanks, but the inadequate French linear defence had given the Germans the opportunity to secure a breakthrough in one place, and the French had therefore to abandon the entire battlefield. This allowed the Germans to recover most of their tanks, of which 111 could be repaired, leaving them with an overall loss of 49 tanks destroyed; the Germans also lost 60 men killed and 80 wounded. Even so, Prioux had achieved his tactical mission and withdrew.

Hoepner now pursued the retreating French without awaiting the arrival of his supporting infantry divisions. His object was to maintain the German pressure on the French and thereby afford them no opportunity to create any coherent defensive line. The German formations pursued the French right to Gembloux, the XVI Corps (mot.) driving straight into the retreating French columns and inflicting heavy losses on them, all the more so as the Germans pursued the French so closely that the French artillery was unable to intervene for fear of 'friendly fire' incidents.

Nevertheless the French were finally able to establish new anti-tank screens and Hoepner, lacking infantry support, had to attack head-on rather than passing round the flanks of the new French positions. During the following Battle of Gembloux on 14/15 May, which pitted the two DLMs, three French motorised divisions, and three French North African infantry divisions against two Panzer divisions and three German infantry divisions, the Panzer divisions reported heavy losses during 14 May and were forced to slow their pursuit. The German attempts to capture Gembloux were repulsed, the Germans suffering slightly more than one-third of their tank strength, together with 304 men killed, 413 wounded and 29 missing against French losses of something more than 2,000 men killed, wounded or missing as well as an unknown number of tanks.

Although they had thus suffered tactical reverses, at the operational level the Germans had managed to divert the Allied 1er Groupe d’Armées from the lower Ardennes area and in the process significantly degraded the Corps de Cavalerie. When news of the German break-out from its bridgehead at Sedan on 15 May reached him, Prioux withdrew from Gembloux and, with the Gembloux gap breached, the XVI Corps (mot.) was not longer needed by Heeresgruppe 'B' and was transferred to Heeresgruppe 'A' as the Heeresgruppe 'B' continued its own offensive to force the collapse of the Meuse river front either by pushing to the west in the direction of Mons, to outflank the BEF and the Belgian formations protecting the Dyle/Brussels sector, or by turning to the south in order to outflank the French 9ème Armée. The French 1ère Armée had suffered heavily and, despite its success in several tactical engagements, was forced to retreat on 15 May as a result of developments elsewhere, leaving its tanks on the battlefield; it was this which allowed the Germans to recover and repair most of their damaged tanks.

By the morning of 15 May Heeresgruppe 'A' had erupted from its bridgeheads over the Meuse at Dinant, Monthermé and Sedan, and the seven Panzer divisions of three corps were free to drive to the west and the coast of the English Channel. The Allies now considered a complete withdrawal from Belgium, which was now seen as little more than a vast trap in the making. The withdrawal would be undertaken in three stages: during the night of 16/17 May to the Senne river, during the night of 17/18 May to the Dendre river, and during the night of 18/19 May to the Scheldt river. The Belgians were inevitably reluctant to abandon Brussels and Leuven, especially as the Dyle river line had up to this time held firm against German pressure, but the Belgian army, the BEF and the French 1ère Armée were either ordered on forced to pull back on 16 May to avoid their southern flanks from being turned by the German armoured forces advancing through the French Ardennes and the 6th Army advancing through the Gembloux gap. The Belgian army, BEF and French 7ère Armée were currently holding the Germans on the KW-Line, and the Belgians believed that had it not been for the collapse of Huntziger’s French 2ème Armée at Sedan, they could have checked the German advance.

The current situation called for the French and British to abandon the strong positions on the Antwerp/Namur line, where they faced only comparatively weak German opposition, for improvised positions behind the Scheldt river. In the south, Lieutenant General Georges François Auguste Deffontaine’s Belgian VII Corps retreated from the areas of Namur and Liége, and in the latter the fortress region put up stiff resistance to the 6th Army. In the north, the French 7ème Armée was diverted to Antwerp after the surrender of the Dutch on 15 May, but was then diverted once again, in this later instance to support the French 1st Army. In the centre, the Belgian army and the BEF were under no real German pressure, and on 15 May the only sector to see significant action being that round Leuven, which was held by the British 3rd Division. After this the BEF was not pursued with any great determination as it pulled back to the Scheldt.

Following the French retirement from the northern sector, the Belgians were left to hold the fortified city of Antwerp. Here four divisions (including the 13th and 17th Reserve Divisions) were faced by the Generalleutnant Moritz Andreas’s 208th Division, Generalleutnant Ernst Schaumburg’s 225th Division and Generalleutnant Hans von Sommerfeld’s 526th Division of von Küchler’s 18th Army. The Belgians successfully defended the northern part of the city, delaying the Germans while starting to withdraw from Antwerp on 16 May, and the city fell on 18/19 May after considerable Belgian resistance. On 18 May the Belgians received word that Namur’s Marchovelette fortress had fallen, and further surrenders were those of Suarlee on 19 May, St Heribert and Malonne on 21 May, and Dave, Maizeret and Andoy on 23 May.

On 16/17 May the British and French withdrew behind the Willebroek Canal as some of the Allied forces in Belgium started to move to the south in the direction of the right flank of the German armoured thrust from the Ardennes. The Belgian I and V Corps also retreated to what the Belgians called the Ghent bridgehead, behind the Dendre and Scheldt rivers. The combination of Belgian infantry and artillery defeated attacks by the 18th Army's infantry but, now significantly outnumbered and outgunned, the Belgians had to abandon Brussels as the government moved to Ostend, and the Germans occupied the Belgian capital on 17 May. It was during the morning of the following day that Hoepner’s XVI Corps (mot.) received instructions to release the 3rd Panzerdivision and 4th Panzerdivision to Heeresgruppe 'A'. This left von Hubicki’s 9th Panzerdivision, attached to the 18th Army, as the only armoured formation on the Belgian front.

By 19 May the Germans were only hours from reaching the French coast of the English Channel. Gort now knew that the French had neither a plan nor the reserves with which to stem the German thrust to the channel. He was also very concerned by the fact that the French 1ère Armée on the BEF’s southern flank had been reduced to disorder and feared that German armour might appear on this army’s right flank at Arras or Péronne, or strike for the channel ports at Calais or Boulogne, or drive to the north-west into the British flank. With its position in Belgium wholly compromised, the BEF considered abandoning Belgium and retreating to Ostend, Bruges or Dunkirk, the latter lying some 6.2 to 9.3 miles (10 to 15 km) inside the French frontier.

Gort’s proposals for a British strategic withdrawal from the continent were rejected by Prime Minister Winston Churchill’s war cabinet and General Sir Edmund Ironside, the Chief of the Imperial General Staff. The general was therefore despatched to inform Gort of the decision and instruct him to conduct an offensive in a south-westerly direction to break through the German axis of advance and join forces with what were deemed the main French forces in the south, though the strongest surviving French forces were actually those in the north. The Belgian army was asked to conform to the plan or, should it chose not to do so, move to channel ports for such evacuation as the British could manage.

The British cabinet also decided that even if it was possible to complete the proposed 'Somme offensive' successfully, it might still be necessary to evacuated some formations, and orders were given to some units may still need to be evacuated, and ordered Vice Admiral B. H. Ramsay, commanding at Dover, to assemble an evacuation fleet: this was the origin of 'Dynamo'.

Ironside arrived at the headquarters of the BEF at 06.00 on 20 May, the day that continental communications between the France and Belgium were cut. When told of the offensive the BEF was to make, Gort responded that it was impossible. Seven of his nine divisions were engaged on the Scheldt river front and, even if he could withdraw them, this would create a gap between the Belgians and British which the Germans would exploit to encircle the Belgians. Moreover the BEF had been on the move and in combat for nine days, and was now short of ammunition. Thus, according to Gort, the main effort to cut off the head of the German armoured thrust to the coast would have to be made by the French from the south.

The Belgian position was made clear by the king, who said that the Belgian army was unable to conduct offensive operations as it lacked tanks and aircraft having been conceived as a defensive force. The king also revealed that in the rapidly diminishing area of Belgium still free of occupation there was food left for only two more weeks. The king did not expect the BEF to jeopardise its own position in order to maintain contact with the Belgian army, but warned that the launch of any southward offensive would result in the overstretch of Belgian capabilities and the effective collapse of the Belgian army would collapse. In these circumstances, Léopold III believed, the best course of action would be to establish a beach-head covering Dunkirk and the Belgian channel ports.

But Gort was forced to comply with Ironside’s orders, even though the BEF committed only two infantry battalions and one armoured battalion to the offensive that gained limited early success but in the Battle of Arras on 21 May failed to sever the head of the German advance from the main body of the German forces.

After this the Belgians were requested to fall back to the Yser river and there to protect the Allied left flank and rear areas. Van Overstraeten said that this was not possible, and that it would in any event lead to the disintegration of the Belgian army. The Allies then suggested another plan, the French asking the Belgians withdraw to the Leie river and the British to fall back to the French frontier between Maulde and Halluin. The Belgians were then to extend their front to make additional elements of the BEF available for the offensive. As part of this movement, the French added, their 1ère Armée would relieve two more Belgian divisions on the right flank. The king was not happy with the prospect, however, as it would result in the abandonment of all but a small portion of Belgium. Moreover, the Belgian army was exhausted, and what was being requested of it represented a great logistical task that would, in any event, take too long to complete.

At this time, the Belgians and the British reached the conclusion that the French were beaten, and that the Allied armies in the pocket on the Franco-Belgian frontier would be destroyed unless something radical was undertaken. Having lost confidence in their allies, the British decided that the survival of the BEF was the most important matter they should plan.

On the morning of 22 May the Belgian front extended some 55 miles (90 km) from north to south, beginning with the Cavalry Corps, which checked its advance at Terneuzen, and the V, II, VI, VII and IV Corps disposed side-by-side along the front; two signal corps guarded the coast. These eight formations were then holding most of the eastern front as the BEF and some of the French forces withdrew to the west to protect Dunkirk, which became vulnerable to German assault on 22 May. The eastern front remained intact, but the Belgians now occupied their last fortified position at Leie. The I Corps, with only two incomplete divisions, had been heavily engaged in the fighting and its continued retention of its position was becoming problematic. On 22 May Churchill, who had been prime minister for just 12 days in succession to Neville Chamberlain, visited the front and pressed for the French and British armies to break out from the north-east and link with what was left of the French army. In this scheme Churchill assumed that the Corps de Cavalerie could and would support the resulting offensive’s left flank. Churchill therefore urged Gort to persuade the Belgians to pull back to the line of the Yser river and make their stand there, the opening of the sluices providing a flooded area which the Germans would find it difficult to cross, and for the BEF and French 1ère Armée to take the offensive at the earliest possible moment (and no later than the following day) on a south-westerly axis in the direction of Bapaume and Cambrai with about eight divisions as well as the Corps de Cavalerie on the British right.

Churchill’s scheme wholly ignored the fact that the Belgians could not withdraw to the Yser, and that there was little chance of any of the Corps de Cavalerie joining in the attack.

The plan for the Belgian withdrawal was sound, for the Yser river covered Dunkirk to the east and south, while the La Bassée Canal covered it from the west. The ring of the Yser also dramatically shortened the Belgian operational area. Such a move would have abandoned Passchendaele and Ypres and would have certainly meant the capture of Ostend, and further reduced the area of free Belgian territory. It would also have resulted in the loss of all Belgian ports, such as Ostend and Zeebrugge, to the east of the Yser.

On 23 May the French attempted a number of small offensives against the German flanks of the axis from the Ardennes to Calais, but were able to achieve no meaningful gains. Meanwhile, under increasing German pressure the Belgians retreated farther, and the Germans captured Terneuzen and Ghent on that same day. The Belgians also had major difficulty in moving such fuel, food and ammunition as they had left: the Luftwaffe had air superiority and made the logistics of everyday life increasingly dangerous. Allied air support could be called in only by radio, and the RAF was now operating from bases in southern England, which made communication still more difficult. The French denied the use of the Dunkirk, Bourbourg and Gravelines bases to the Belgians, who had initially been assured of their availability for Belgian purposes. Thus the Belgians had to use the only harbours left to them, namely Nieuport and Ostend.

Churchill and Général d’Armée Maxime Weygand, who had by now assumed supreme command from Gamelin, were both still determined to break the German line and extricate their forces to the south. When they communicated their intentions to Léopold III and Van Overstraeten on 24 May, the latter was stunned, all the more so as a dangerous gap was starting to open between the British and Belgians between Ypres and Menen, thereby threatening the remnant of the Belgian front. The Belgians could not cover the emergent gap as this would have overstretched them. Without consulting the French or asking permission from his government, Gort immediately ordered two of his divisions (Major General H. E. Franklyn’s 5th Division and Major General G. le Q. Martel’s 50th Division) to plug the gap and abandon any offensive operations farther to the south.

On the afternoon of 24 May, von Bock had committed four divisions of von Reichenau’s 6th Army against the Belgian IV Corps' position in the Kortrijk area of the Leie and, despite determined Belgian resistance, the Germans managed to cross the river at night and push forward to a depth of 1 mile (1.6 km) along a 13-mile (21-km) front between Wervik and Kortrijk. With superior numbers and operating under total air superiority, the Germans had thus secured a significant bridgehead, though in the process they had suffered a high level of casualties. The Belgian 1st, 3rd, 9th and 10th Divisions then arrived and delivered several counterattacks, but the Belgian infantry and its supporting artillery were then heavily attacked by the Luftwaffe and compelled to retreat. The German bridgehead dangerously exposed the eastern flank of Major General D. G. Johnson’s (from 25 May Major General T. R. Eastwood’s) 4th Division, and Montgomery dispatched several units of his 3rd Division (including the two battalions of the Middlesex Regiment and the 99th Battery, 20th Anti-Tank Regiment) as an improvised defence for this threatened area.

A critical point of Weygand’s overall plan, and also of the British government’s argument for a thrust to the south, was the withdrawal of forces with which to prosecute the Arras offensive, though this had left the Belgian army overextended and was therefore instrumental in its collapse. The Belgians had necessarily to cover areas within the BEF’s area of responsibility so that the British could redeploy forces for the offensive, and the collapse could have resulted in the loss of the Channel ports behind the Allied front, so resulting in a complete strategic encirclement and, in the absence of ports for an evacuation, final surrender. The Belgians felt that the British could have done more to counterattack von Bock’s left flank to relieve the Belgians as Heeresgruppe 'B' attacked across the fortified British position at Kortrijk: in fact the Belgian high command made at least five appeals for the British to avert possible disaster by attacking the vulnerable left flank of the German divisions between the Scheldt and Leie rivers.

No attack was made, and the Germans were able to bring up reserves to cover the gap between Menen and Ypres. This nearly led to the isolation of the Belgians from the British. The 2nd Cavalry Division and the 6th and 10th Divisions frustrated the German attempts to exploit the gap, but the situation nevertheless remained critical.

On 26 May 'Dynamo' started for the evacuation of major British and French contingents to the UK. By that time ships of the Royal Navy had already withdrawn 28,000 rear-area British troops. Boulogne had fallen to the Germans, and Calais was about to fall, which left Dunkirk, Ostend and Zeebrugge as the only viable evacuation ports. The German advance already threatened Ostend, and to the west elements of Heeresgruppe 'A' had reached the outskirts of Dunkirk and were a mere 4 miles (6.4 km) from its centre on the morning of 27 May, so bringing the port within artillery range.

On 27 May the situation had changed considerably from that of just 24 hours earlier. The Belgian army had been driven from the Leie river line on 26 May, and Nevele, Vynckt, Tielt and Iseghem had fallen on the western and central parts of the Leie front. In the east, the Germans had reached the outskirts of Bruges, and captured Ursel. In the west, the line between Menen and Ypres had been penetrated at Kortrijk, and the Belgians were now using railway rolling stock to help form anti-tank defences on a line from Ypres to Roulers via Passchendaele. Farther to the west the BEF had been forced back, in the area to the north of Lille just over the French border from Belgium, and was now in danger of allowing a gap to develop between themselves and the Belgian southern flank on the line between Ypres and Lille. The danger inherent in a German advance to Dunkirk would mean the loss of the port, and the threat was so great that the British withdrew to the port on 26 May. In doing so, they exposed the French 1ère Armée’s north-eastern flank near Lille. The Germans advanced as the British retreated, encircling the bulk of the French 1ère Armée. Both Gort and Pownall, his chief-of-staff, accepted that their withdrawal inevitably meant the destruction of the French 1ère Armée.

The fighting of 26/27 May had brought the Belgian army to the very brink of collapse. The Belgians still held the lines from Ypres to Roulers in the west, and between Bruges and Thelt in the east, but on 27 May their centre collapsed in the sector between Iseghem and Thelt. There was now nothing to prevent a German thrust to the east to take Ostend and Bruges, or to the west to take the ports at Nieuport and De Panne, deep in the Allied rear. The Belgians had exhausted all they had to continue their resistance, but even so managed to hold in several places after British withdrawals. One such place was the Scheldt river line, where they relieved Major General A. E. Percival’s British 44th Division and allowed the British to retire through the Belgian ranks.

What was left of the Belgian was stretched from the coastal town of Cadzand on the Dutch side of the Belgian/Dutch frontier to the south in the direction of Menin on the Leie river, and to the west from Menin to Bruges, but lacked any reserve. With the exception of a few RAF sorties, the Luftwaffe had command of the air and could deliver attacks where and when they desired. There were no further natural obstacles between the Belgians and Germans, and further Belgian retreat was impossible as they remained no place into which a retreat could be made. The Luftwaffe had destroyed most of the Belgian railway network to Dunkirk, and just three roads were left: these were the roads from Bruges to Thourout and Dixmude, from Bruges to Ghistelles and Nieuport, and from Bruges to Ostend and Nieuport, but movement along these three axes was all but impossible because of the German air supremacy. Water supplies were damaged and cut off, and there was no supply of gas and electricity. The canals had been drained and were now in service as supply dumps for whatever ammunition and food were still left. The total area still free of the Germans comprised a mere 655 sq miles (1700 km²), in which there existed, though barely, the remnants of the Belgian military as well as 3 million civilians.

Léopold III knew that further resistance was pointless, and during the evening of 27 May requested an armistice.

Vessels of the Royal Navy evacuated the Belgian general headquarters from Middelkerke and St Andries, east of Bruges, during the night, but the king and his mother, Queen Elisabeth, remained in Belgium to endure five years of self-imposed captivity. The Belgian surrender came into effect at 04.00 on 28 May.

The Belgian casualty figures for the Battle of Belgium, between 10 and 28 May, are not known, but the total Belgian losses up to the time of the surrender included 6,093 men killed in action (another 2,000 died while prisoners of war), 15,850 wounded and 200,000 taken prisoner; the Belgians also lost 112 aircraft.