As the French mechanised infantry regiments had three mechanised infantry battalions, the total infantry strength of the Corps de Cavalerie was six battalions, while the XVI Corps (mot.) had seven motorised infantry battalions. The French units were only lightly equipped with anti-tank guns: 12 25-mm and eight 47-mm SA 37 guns per division, and their anti-aircraft guns were six 25-mm guns per division. There was a significant imbalance in artillery: the French light mechanised divisions each had 36 pieces of artillery against the German division’s 68 pieces including 24 75-mm (2.95-in) leichtes Infanteriegeschütz 18 weapons. This was not offset by corps artillery: the German corps had four attached artillery regiments and a heavy battery, while the French corps possessed only two 75-mm (2.95-in) field gun regiments and one group of 12 25-mm anti-tank-guns as corps troops.

Generalmajor Wolfram Freiherr von Richthofen’s VIII Fliegerkorps, a specialised close support and ground attack formation, had some 300 Junkers Ju 87 single-engined dive-bombers and 42 Henschel Hs 123 single-engined biplane ground attack aircraft as well as about 130 Messerschmitt Bf 109 single-engined fighter aircraft, and stood ready to support the Panzers. Generalleutnant Alfred Keller’s IV Fliegerkorps and Generalmajor Joachim Coeler’s 9^th Fliegerdivision added some 280 medium bombers and more than 500 Bf 109 fighters and Messerschmitt Bf 110 twin-engined heavy fighters, some of which would also be at Hoepner’s disposal.

Billotte suggested to Prioux that he might move his armour farther to the east to support the Belgian army, but Prioux, unimpressed by the Belgian defence and fearing to concentrate his force in the open when the Germans had air superiority, preferred to deploy his dragoons and supporting arms farther back in a line of strongpoints, with his tanks behind them to counterattack German penetrations. Billotte accepted his decision and, impressed by the need for haste, added that the 1er Groupe d’Armées would advance by day as well as by night, despite the German air threat, in order to reach Gembloux. Thus Prioux needed to check the German armour only until dawn on 14 May.

At 11.00 on 11 May, Billotte diverted most of the French 23ème Groupement de Chasse’s fighters to cover the advance of the 1ème Armée and neighbouring formations. After many of the French fighters had been removed to escort bombers, few fighters were available to cover the cavalry. The Allied bombers concentrated their efforts on slowing the dangerous advance of the XVI Corps (mot.)'s tanks. Prioux’s ground reconnaissances units fell back before the German armour toward the main body of French cavalry, which was established in strongpoints along a 25-mile (40-km) front with the 2ème Division Légère Mécanique from Huy on the Meuse river and north, then westward along the Mehaigne stream. The 3ème Division Légère Mécanique formed a front from the area of Crehen to Orp and then northward along the Petite Gette stream to the area of Tirlemont. The battlefield which Prioux chose was a plateau with occasional woods, a dense road network, extended settlements and a few isolated large farms. The Mehaigne and Petite Gette were small streams flowing within rock cuts between 6.5 and 10 ft (2 and 3 m) deep with many crossing points, often fordable by tracked vehicles, and offering good cover for infiltration. The key terrain feature, however, was the ridge running from Hannut through Crehen and Merdorp. To the north of the ridge, the Petite Gette stream flowed to the north into the Escaut river, and to the south of it the Mehaigne stream flowed to the south into the Meuse river. This ridge formed a natural corridor for the movement of mechanised forces.

By placing the 3ème Division Légère Mécanique on a 10.6-mile (17-km) front, only 6.8 miles (11 km) were partially covered by anti-tank obstacles. Prioux was straining the limits of French doctrine. The French cavalry manual of 1939, in part authored by Général de Division Jean Langlois who now commanded the 3ème Division Légère Mécanique, had considered the case of a division légère mécanique assigned to mask a breach in the front until reinforcements could arrive. In such a circumstance, the manual ruled, command was to be decentralised, the division should place a combined-arms force on each flank of any possible penetration, then the commander would move his artillery and his reserves to maintain a continuous line of fire. If the opponent attacked in force along the whole front, however, this defence would transform itself into a manoeuvre of retreat. The manual added that a division légère mécanique could retreat on a front of no more than 6.25 to 9.33 miles (10 to 15 km) over average terrain. In the event of the front’s extension, the absence of anti-tank obstacles and a powerful opponent, a withdrawal was to be made. French doctrine warned that on a wide front on open terrain against massed armour, the division légère mécanique was to abandon the decentralised defence and to concentrate its forces for action. Prioux did not follow these directions.

The French command articulated its cavalry front on 11 May. On the left was Langlois’s 3ème Division Légère Mécanique, whose front was divided into northern and southern sectors. The northern sector, commanded by Colonel Dodart des Loges, had, from north to south, the 12ème Cuirassiers, which was the divisional reconnaissance regiment, in touch with British and Belgian cavalry in the Tirlemont area, then a line of two battalions of the 11ème Dragoniers: this has its 3ème Bataillon holding a 3.75-mile (6-km) front along the Petite Gette stream around Opheylissem, with 21 Hotchkiss tanks plus another such squadron from the Cuirassiers' 1er Bataillon and supported by 21 75 mm guns from the Corps de Cavalerie’s reserve; and the 2ème Bataillon holding 3.1 miles (3 km) along the Petite Gette stream southward to Orp, similarly with its own Hotchkiss tanks as well as another squadron of the 1er Cuirassiers and supported by 12 75-mm (2.95-in) gins of the 76ème Artillerie. Behind this sector stood one squadron of SOMUA tanks of the 1er Cuirassiers at Marilles. General de Lafont commanded the 3.1-mile (5-km) southern sector of the division astride the dangerously open terrain facing Hannut. Lafont had the 1/11ème Dragoniers in strongpoints at Thisnes, Wansin and Crehen, with their Hotchkiss squadrons plus an additional Hotchkiss squadron each in Crehen and Thisnes from the 2ème Cuirassiers, supported by 21 75-mm (2.95-in) artillery guns and 12 105-mm (4.13-in) guns of the 76ème Artillerie. One SOMUA squadron of the 1er Cuirassiers at Jauche and two such squadrons of the 2ème Cuirassiers at Jandrenouille and Merdorp constituted the sector’s reserve. To the south of Crehen the 2ème Division Légère Mécanique was in position, covered along almost the whole of its front by the Mehaigne stream, down to Huy on the Meuse river.

On 12 May, the 4^th Panzerdivision raced to seize Hannut, its first objective, and reached the area during that morning. Hoepner ordered the 3^rd Panzerdivision and 4^th Panzerdivision to concentrate on and secure Hannut in order to secure the flank of the corps' parent formation, Generaloberst Walter von Reichenau’s 6^th Army. Noting his lack of fuel and the fact that his division’s artillery and infantry support had not yet caught up with the armour, which rendered risky any immediate assault on Hannut, Stever called for an air-drop of fuel for his 4^th Panzerdivision. Concluding that he was facing only one French battalion, he engaged the French defences. That morning the 4^th Panzerdivision made contact with a French armoured force of some 25 tanks, destroying seven of the French tanks for no losses.

Allied air units also concentrated on his formation, which could have made Stever’s mission more difficult. The RAF sent 38 bombers and lost 22 of these. The Armée de l’Air made two large bombing attacks, one including 18 of its Bréguet Bre.693 twin-engined ground-attack aircraft on their maiden mission, and lost eight aircraft. The 85 Bf 109 fighters of Oberstleutnant Max Ibe’s Jagdgeschwader 27 flew 340 sorties on that day, claiming 26 Allied aircraft for the loss of four fighters. German anti-aircraft guns claimed another 25 Allied aircraft. But that afternoon Général d’Armée Alphonse Joseph Georges, commander-in-chief of the Allied forces in north-western France, suddenly ordered air priority away from the Belgian plain to the threatened centre of his front farther to the south in the Sedan area. Prioux’s cavalry formations were now left with little air cover.

Having surrendered the initiative and with only limited air reconnaissance available to him, Prioux could only wait to see where the German armour would concentrate. His right flank he anchored on the Meuse river. He held Huy with two battalions of motorised heavy infantry plus some dragoons and artillery. His left was in touch with British light cavalry and parts of the Belgian cavalry corps delaying the Germans along the axis from St Trond to Tirlemont. German armoured cars, followed by infantry infiltrations, probed toward Tirlemont during the afternoon, leading the Corps de Cavalerie to order a squadron of tanks as well as one of the divisional reconnaissance groups to the area. British reinforcements also reached the scene. The German effort was essentially a reconnaissance and diversionary probe. The main preoccupation of both sides was the open area around Hannut.

On the ground, Stever’s 35^th Panzerregiment was advancing toward Hannut and encountered fierce resistance. The French armour was deployed under cover and during the battle counterattacked several times. The French forces then yielded Hannut without a fight. The Germans attempted to outflank the town, unaware of the retreat. Some 50 German light tanks ran into the French strongpoint at Crehen, where the French defence was based on 21 Hotchkiss tanks of the 2ème Cuirassiers, supported by parts of the 76ème Régiment d’Artillerie plus fire from the nearby 2ème Division Légère Mécanique. The dragoons lost heavily, but it was the Hotchkiss tanks which carried the burden of the defence, despite the loss of their commander. Firing from prepared positions, German medium tanks attempted to pin the French while the light tanks moved around the French position. The main French force then retreated to Merdorp. The encircled 2ème Cuirassiers were freed by an armoured counterattack by the 2ème Division Légère Mécanique: S35 tanks breached the German line and the French units broke out, suffering heavy losses in the process. The right flank of the 4^th Panzerdivision was now dangerously exposed.

Rushing from the German staging area at Oreye, some 6.8 miles (11 km) to the north-east of Hannut, the 3^rd Panzerdivision moved to cover this threat. At 16.30 the 6^th Army requested air reconnaissance, and the Luftwaffe then reported French armour at Orp and motorised units at Gembloux. Reichenau ordered Hoepner to send his XVI Corps (mot.) forward to Gembloux in order to prevent the French from organising a defence, but Hoepner continued to worry about his lengthy supply lines and more especially his exposed flanks. General Viktor von Schwedler’s neighbouring IV Corps had elements in the area of St Trond probing toward Tirlemont, a fact which concerned Prioux, but General Alfred Wäger’s XXVII Corps was still held up in the area to the north of Liége some 23.5 miles (38 km) to the east of Hannut, leaving Hoepner’s southern flank exposed.

The German solution was to construct an advance guard of one Panzer battalion and one infantry battalion supported by two artillery groups to push forward, if possible, to Perwez some 11.2 miles (18 km) to the south-west of Hannut. But Stever ordered this advance guard that if it encountered serious resistance it should bring its attack to a halt. The force advanced under heavy air and artillery cover against the French strongpoint at Thisnes, and simply ignored the French counterattack at Crehen in its rear. The streets of Thisnes were barricaded. Heavy French artillery and other fire met the attack, stopping the tank company in the German van. The rest of the German force flanked the French position to the right, though poor visibility hampered the movement. The advance guard finally reached the western edge of the town, only to be met by heavy artillery fire from the neighbouring French strongpoint in Wansin, and which continued to increase. The advance force was ordered to regroup its armour and infantry and to secure a perimeter. But before this could be done, S35 tanks counterattacked, knocking out the tank of the Panzer regiment’s commander. After hard fighting, both the French and German tanks pulled back in the darkness, stumbling into each other on occasion. The French retreated to Merdorp and the Germans to the Hannut area.

At 20.00 Stever spoke with Hoepner, telling him he was certain that two French mechanised divisions were in front of his division, one to his front and one behind the Mehaigne river. Hoepner and Stever agreed to mount a major attack on the following day. According to the plan the 4^th Panzerdivision would concentrate to Gembloux’s right and operate jointly with the 3^rd Panzerdividion, which would receive air support from the VIII Fliegerkorps.

The Germans attacked during that night, testing the French defences. The French strongpoint at Wansin fought all night against German infantry before withdrawing in the early hours of 13 May. The front of the 3ème DLM remained, holding positions near Tienen, Jandrenouille and Merdorp. The 2ème DLM also held its original front. The only breach of the line was at Winson on the junction between the 2ème DLM and 3ème DLM. Hoepner had failed to take his objective.

To the south-east of the plain, German forces had begun their assault over the Meuse river as the primary German effort of the campaign. To the north, Hoepner launched spoiling attacks and tied down the powerful 1ère Armée to the extent that this latter could not intervene. Hoepner believed the newly arrived 3^rd Panzerdivison faced only weak opposition; the 4^th Panzerdivision, on the other hand, Hoepner believed to be faced by strong French mechanised forces at Hannut and Thisnes, which the French had in fact already abandoned, and possibly a second French mechanised division to the south of the Mehaigne stream. The Luftwaffe struck late in the morning to soften the French defences, and the 3^rd Panzerdivision advanced on Thorembais. The 4^th Panzerdivision was to move in parallel on Perwez against an expected strong Belgian anti-tank line. The XVI Corps (mot.) thus fell back on the 6^th Army's instruction to push immediately on Gembloux.

The 12ème Cuirassiers and, to the south, the 3/11ème Dragoniers fought off waves of armour-supported German infantry. Armoured vehicles, but even so Generalmajor Friedrich-Carl Cranz’s 18^th Division managed to penetrate their positions. The French command planned to counterattack with tanks of the 1er Cuirassiers to restore the line, but then abandoned the scheme as a result of developments on the rest of the 3ème Division Légère Mécanique’s front. In the afternoon the French command ordered a retreat in which the Allied force escaped as the German infantry was too slow in following its initial success. The 2ème Division Légère Mécanique was positioned just to the south of the planned axis of Hoepner’s attack, and early in the morning sent some 30 S35 tanks from the Mehaigne stram to the line between Merdorp and Crehen to relieve the pressure on the 3ème Division Légère Mécanique. The attack was repulsed by heavy German tank and anti-tank fire near Crehen, and the French suffered crippling losses. Bougrain, commanding the 2ème Division Légère Mécanique, signalled that German infiltrations and attacks by armoured cars over the Mehaigne river at Moha and Wanze, just to the north of Huy, threatened to cut off the large Belgian garrison in Huy. Bougrain therefore diverted his tank reserves to try to retrieve the situation. At 15.00 a French reconnaissance aeroplane reported large concentrations of German armour to the south-east of Crehen, but the 2ème Division Légère Mécanique no longer had reserves available for any intervention.

Bougrain’s dragoniers and motorised infantry were strung out in a series of isolated strongpoints and thus were vulnerable to infiltration. Bougrain refused the offer of the Belgian III Corps, retreating through his front from the area of Liége, to reinforce his troops on the Mehaigne river. Prioux’s lack of attention to French defensive doctrine and concentration had allowed decentralised command to continue in a process which damaged the French operational performance and thus created problems for the French defence.

For its part, the German command, concerned with the possibility that the 2ème Division Légère Mécanique could interfere with its main attack, juggled its marching infantry units between its XVI Corps (mot.) and the XXVII Corps, and scraped together four units from Generalleutnant Wolfgang Reinhard’s 35^th Division, Generalleutnant Siegfried Hänicke’s 61^st Division and Generalleutnant Ernst-Eberhard Hell’s 269^th Division advancing via Liége, along with air support and some armoured cars. These forces infiltrated between the French strongpoints to the north of Huy and drew out Bougrain’s armour. This German success-was critical, for it tied down the French armour, and made it possible for Hoepner to concentrate strength against Prioux’s front in the area to the west of Hannut. Had he concentrated his armour for an advance to the north or north-east, Bougrain might have caused untold problems for the German plan. But Prioux gave him no such mission.

The real focus of the battle on 13 May lay in the area to the west of Hannut. Busch ordered Hoepner not only to break through to Gembloux, but to pursue the French forces to the west of that position. Hoepner concentrated all of his XVI Corps (mot.)'s armoured strength and infantry battalions, the former including about 560 operational tanks, aided on their right by Cranz’s 18^th Division of von Schwedler’s IV Corps, on a front of some 7.5 miles (12 km) with the 3^rd Panzerdivision in the north facing Marilles and Orp, and the 4^th Panzerdivision in the south facing Thisnes and Merdorp. Oberst Friedrich Kühn’s 3^rd Panzerbrigade of the 3^rd Panzerdivision moved out at about 11.30 with its 5^th Panzerregiment on the right and 6^th Panzerregiment on the left, and Kühn moved forward with the 5^th Panzerregiment. By 12.00 the German armour was in action in the barricaded and mined towns along the Petite Gette stream. After 90 minutes of heavy fighting, both Panzer regiments succeeded in pushing elements of the French defenders over the stream, the 5^th Panzerregiment before Marilles and the 6^th Panzerregiment at Orp. The German command ordered most of the 6^th Panzerregiment to wheel to the south toward Jandrain and Jandrenouille, where the terrain was more favourable and it could aid the 4^th Panzerdivision. Operating on the eastern and western banks of the Petite Gette stream, the 6^th Panzerregiment ran into French armour in the area of Orp, and was then attacked by more French armour, but the German battalions then combined to defeat the attack.

The German forces attacked during the afternoon, the 3^rd Panzerdivision in the north facing Marilles and Orp, and the 4^th Panzerdivision in the south facing Thisnes and Merdorp. Oberst Hermann Breith’s 5^th Panzerbrigade and the 6^th Panzerbrigade of the 3^rd Panzerdivision faced an attack by French armour, the two sides clashing with each on the offensive. The German tanks were numerically superior and could be seen moving in large formations, while the French armour operated in small groups and fired more slowly. Between 15.00 and 15.48 the 3^rd Panzerbrigade issued repeated and urgent calls for anti-tank units and the Luftwaffe to deal with the French tanks. The 2/5^th Panzerregiment, still opposite Marilles, suddenly found itself attacked on its flank and rear by superior French armoured forces. The 3^rd Panzerbrigade's war diary recorded the 15 minutes during which the 2/5^th Panzerregiment stood alone. The 1/5^th Panzerregiment, seeing victory on the left, sent much of its strength back to the right, bringing the fight before Marilles to a successful conclusion at about 16.00. As infantry secured Orp, the Panzer units called for urgent resupply with 37- and 75-mm ammunition for their PzKpfw III and PzKpfw IV tanks.

That morning the strongpoints of the 2/11ème Dragoniers suffered serious losses to air and artillery bombardment, while German motorcyclists followed by armoured cars searched for infiltration and crossing points. From about 11.30, the 3ème Division Légère Mécanique signalled that its units could see some 80 Panzers opposite Marilles and some 100 before Orp. The dragoons defended their strongpoints with the support of their organic Hotchkiss squadron, but their resistance began to crumple at about 13.30 in the face of German numbers and their own lack of ammunition.

Colonel Dodart des Loges, commanding the northern sector of the 3ème Division Légère Mécanique’s front, ordered a retreat, As the remaining dragoons withdrew, their H35 tanks and two Hotchkiss squadrons of the 1er Cuirassiers counterattacked and drove the German armour back to the stream. Losses were about even, the French claiming six Panzers destroyed for the loss of four of their own number. Colonel de Vernejoul, commanding the 1er Cuirassiers, despatched 36 SOMUA S.35 tanks to halt the German armour advancing from Orp toward Jandrain, but the German armour then surprised the French tanks as they attacked. An equal number of Panzers attacked from cover, and the French attack was defeated.

This attack was the principal effort of the 3ème DLM to check the 3^rd Panzerdivision. The 2ème DLM launched raids against the still vulnerable flanks of the 4^th Panzerdivision, and some small groups of French tanks broke through but were quickly defeated by the 654^th Panzerabwehrabteilung attached to the 4^th Panzerdivision. Apart from these isolated and intermittent raids, the 2ème Division Légère Mécanique made no further attempts to attack the flank of the 4^th Panzerdivision.

In the afternoon, the 4^th Panzerdivision began an assault on Medorp. As the French artillery opened fire and the German artillery responded, the French pushed armour into the abandoned town and skilfully changed position, making the Panzers struggle to locate and strike their targets. The German armour decided to bypass the town round its left flank, but this exposed the German infantry, which was thus forced to give ground in the face of encroaching French armour. The Panzers quickly turned and engaged the French in the open. Initially the French tanks held the advantage as a consequence of their superior armour and firepower, but superior German tactics, which concentrated the attack of their armour on the vital point, quickly began to tell. Small groups of French infantry infiltrated and attacked from the rear, but the German infantry crushed any resistance.

At this point the 3^rd Panzerdivision and 4^th Panzerdivision were advancing on Jandrain, outside which there developed a bitter tank battle. The Panzers prevailed through numbers and reported 22 French SOMUA S.35 tanks totally destroyed. The German forces thus secured both the town and the area round it. The German forces reported the capture of 400 men, and the seizure of four and five tanks. At this point the French forces, in the form of the 2ème Division Légère Mécanique and 3ème Division Légère Mécanique, began a general retreat to the west. The Panzer divisions, no longer fearing any attack on their flanks, advanced and engaged the French remnants in the evening. The 3^rd Panzerbrigade reported its destruction during the day of 54 French tanks, 36 of them by the 5^th Panzerregiment and the other 18 by the 3^rd Panzerregiment. Its own losses were listed as 'slight'. The 6^th Panzerregiment reported a provisional total of only two tanks lost. The Germans suffered many more tanks disabled, however, but as they secured the battlefield they were able to recover many others for resuscitation and return to service. The remainder of the 3ème Division Légère Mécanique was in line behind the Belgian anti-tank obstacle on the front between Beauvechain, La Bruyere, Pietrebais-Incourt and Perwez. During the morning of the next day, the 2ème Division Légère Mécanique fell back into the line in the area to the south of Perwez.

The German attack on Perwez took place during the morning of 14 May. Stumpff’s 3^rd Panzerdivision was to engage the new Allied line near Gembloux while Stever’s 4^th Panzerdivision was to break through the centre of the Allied line at Perwez. Hoepner ordered the attack to begin without infantry support, but the German armour could not break through the French positions.

The 4^th Panzerdivision engaged French armour, which resisted strongly in wooded areas round Perwez. After hard fighting, the French defences were destroyed with the help of the German infantry. The 1ère Armèe had redistributed and spread its tank battalions behind the infantry and now, spread out and unsupported, they were defeated in detail by the concentration of numerically superior German combined-arms teams.

The 3^rd Panzerdivision was brought to a halt by the fierce resistance of the 2ème Division Légère Mécanique. Bitter fighting resulted and the appearance of large numbers of French tanks almost panicked the German commanders into thinking a major counterattack was developing, when in fact these French activities were merey rearguard actions. Both sides suffered significant armour losses, but as night fell the 2ème DLM halted its rearguard actions and the German commanders regained their composure. The Allied forces had gained themselves time to reorganise their forces to respond to another major German assault on 15 May.

The PzKpfw III and PzKpfw IV were the only German tanks that could outmatch the S35 in combat. This French tank was generally considered to be one of the most formidable tanks of the campaign in the west. German tactics proved superior, however: by using radio to co-ordinate manoeuvres, the Germans outwitted the French, who were limited to rigid, static positioning. The French tanks could not communicate with equal fluidity or rapidity. The French missed tactical and operational opportunities and were poorly co-ordinated. Each of the German tanks was also manned by a larger crew, so the commander could concentrate on command tasks rather than gunnery, while the French tank commanders had to act as gunner and assistant gunner.

The German plan failed to forestall the 1ère Armée at Gembloux, despite their victory over the 3ème DLM. The German advance to the Belgian plain had tied down the Corps de Cavalerie and part of the 1ère Armée while the main German assault crossed the Meuse river at Sedan farther to the south-east. The Germans had hoped that Hoepner’s armour and the neighbouring corps would pin and neutralise the threat of the 1ère Armée, but on 15 May elements of the 1ère Armée settled more fully into position, checked the German armour, gaining time and space to manoeuvre. Part of the 1ère Armée sacrificed itself at the siege of Lille and held up the bulk of the German armour, which had broken through to the south-east, enabling the British Expeditionary Force and other French formations to escape to England from Dunkirk.