The Sloedam occupied a position of immense strategic importance. It represented the final land connection between the islands of Zuid-Beveland and Walcheren and, consequently, the last major obstacle standing between the German forces and the heart of Walcheren.
As noted earlier, the causeway provided the only direct route across the Sloe. Although light infantry could, in theory, cross the mudflats on either side of the dam, such an undertaking was hazardous. Large stretches of the terrain consisted of deep mud and marshland, where men could easily become trapped or even drown. As a result, the causeway itself remained the only practical avenue for a large-scale advance.
The geography of Walcheren in 1940 differed considerably from that of today. Modern Middelburg extends across both sides of the 'Kanaal door Walcheren' (Canal through Walcheren), but at the time the city lay entirely on the western bank. The road and railway crossing the Sloedam led directly toward Middelburg before turning south toward the port city of Flushing (Vlissingen).
The landscape itself has also changed dramatically. Much of the Sloe - the stretch of water between Lewedorp and Arnemuiden - has since been reclaimed and enclosed. The causeway that formed the focal point of the 1940 battle now corresponds largely to the route of the modern A58/E312 motorway. Readers using contemporary maps rather than wartime maps should therefore be aware that the current terrain bears little resemblance to its appearance during the campaign, which can easily lead to confusion.
Despite the setbacks suffered during the preceding days, French General Deslaurens remained cautiously optimistic about the prospects of defending the Sloedam. From a military standpoint, it was a naturally strong defensive position. The narrow approach channelled any attacker into a confined corridor, while the surrounding mudflats severely restricted manoeuvre. Moreover, the defences had recently been reinforced with several modern APX 47 mm anti-tank guns, providing the defenders with an effective means of engaging any German armoured vehicles attempting to force the crossing.
Given these advantages, Deslaurens believed that his troops stood a reasonable chance of holding the position for a considerable period. Whether the defenders possessed the morale, discipline, and resources required to exploit those advantages remained another matter entirely.
Over the past decade, renewed interest in the events that unfolded in Zeeland during those dark days of May 1940 has led to a significant increase in historical research. Additional funding became available, and a growing number of historians and independent researchers devoted their attention to the campaign. The results have proven both valuable and thought-provoking.
Research conducted by several respected historians culminated in important publications in 2010 and 2012. These studies challenged elements of the traditionally accepted narrative surrounding the Battle of the Sloedam and, in particular, the destruction of the historic centre of Middelburg. For decades, it had generally been assumed that German artillery and air attacks were responsible for the devastation of the city's ancient core. More recent investigations, however, have pointed towards a less popular and more controversial conclusion.
The evidence for deliberate German shelling or bombing of Middelburg appears increasingly weak. In fact, as researchers reconstructed the events in greater detail, the theory of German responsibility became progressively less convincing. In 2012, a local historian presented a carefully documented case suggesting that the destruction was more likely caused by French artillery fire - particularly the mobile land-navy battery with Schneider (Model 1932) 155 mm guns with a range of up to 25 km - intended to cover the Allied withdrawal from the Breskens site.
His research drew upon a substantial body of evidence. French archival records indicate that heavy batteries south of Middelburg were firing at key exit routes from the city while retreating French artillery units also shelled areas within the urban centre. In addition, reports concerning unexploded shells recovered after the battle identified several as being of French origin. These findings lend considerable support to the argument that French artillery rounds were responsible for igniting the fires that ultimately devastated the city.
Further evidence emerged from analyses of shell impact patterns. The trajectories of many projectiles pointed to origins south and south-west of Middelburg, rather than from the east, where German batteries would have been positioned. Perhaps most telling is the timing of the destruction. The most severe fires broke out late in the day, at a stage when German forces were concentrating their efforts on breaking through the Allied positions around the Sloedam and advancing toward Flushing. At that point, there appears to have been little military reason for the Germans to direct significant fire against Middelburg itself.
Conversely, French forces retreating toward Walcheren's western exits had every reason to employ covering artillery fire in an attempt to slow the German advance. According to this interpretation, it was this artillery fire - rather than German bombardment - that ignited the catastrophic fires which consumed much of the historic city centre.
The studies published in 2010 and 2012 were supported by extensive scholarly research and rigorous source analysis. Their conclusions have not ended the debate, but they have significantly altered it.
Two battalions of the French 224th Infantry Regiment (224e RI) were deployed at the western end of the Sloedam and in the surrounding area. General Deslaurens adopted a defence-in-depth scheme, in accordance with established French military doctrine.
The first line of defence consisted of two companies tasked with holding the causeway itself. They were supported by several heavy machine-gun positions and three or four anti-tank guns, armed with both Hotchkiss 25 mm and APX 47 mm weapons. The dikes flanking the causeway on either side were also densely occupied by French infantry. The remainder of the western shoreline was covered by patrols, as the broad southern expanse of the Sloe was considered a less likely crossing point for a German assault.
The causeway itself had neither been mined nor prepared for demolition. No minefields had been laid along its embankments. French engineers had erected a number of improvised barricades, but these hastily constructed obstacles would have posed little difficulty to a determined attacker. Using Dutch explosives, however, the engineers did block both the road across the causeway and the railway line that ran alongside it.
For a time, the French command considered reinforcing Walcheren with additional troops. In the end, however, it was concluded that the strategic situation no longer justified such a commitment. Reinforcements were therefore withheld. The defence of the Sloedam was regarded as the last position of real military value. Should it fall, a general withdrawal of all the French forces from Walcheren would inevitably follow. Indeed, preparations for such a retreat were already underway, as French commanders recognised that they could not maintain their position indefinitely giving the developments of the German campaign elsewhere.
By this stage of the campaign, the original strategic objectives had already been lost. The attempt to secure Antwerp and control the approaches to the Scheldt had failed. Consequently, the continued fighting on Zuid-Beveland and Walcheren served only one remaining purpose: to protect the northern flank of the French forces operating north of Antwerp and to delay the German advance for as long as possible so that Allied troops could be taken back in a controlled manner and pace.
The Germans encountered greater difficulty overcoming the canal near Kapelle in their rear than they did confronting the opposing forces. The canal's steep and elevated embankments made the construction of conventional pontoon bridges impractical. Nevertheless, during the night, German engineers assembled a number of effective ferry crossings using bridging equipment, allowing heavy weapons and supplies to be transported across.
In the early hours of 17 May, twelve 10.5 cm Rheinmetall light howitzers of the SS Artillery Regiment were ferried to the western side of the canal. Later that morning, an engineered bridge became operational, enabling the transfer of the newly attached II./AR.629, a mixed heavy artillery battalion equipped with four heavy 10.5 cm guns and eight 15 cm howitzers. An identical formation, II./AR.54, would join them later in the afternoon.
The logistical difficulties caused by the canal crossing delayed the German preparations and ultimately forced a postponement of the main assault on the Sloedam. Neither the infantry battalions nor the artillery were fully in position at dawn, and the principal attack was therefore postponed until 0930 hours. In the meantime, German commanders believed there was a reasonable chance that, as on previous days, the Allied defenders might be driven off by relatively limited pressure.
Before the Germans could launch their assault, however, they found themselves on the receiving end of a tactic they had employed so effectively throughout the campaign. Dive bombers of the French Navy - Vought 156F aircraft of AB.1 and Loire-Nieuport LN-401 aircraft of AB.2 - attacked German positions east of the Sloe, dropping 225 kg (500 lb) bombs. German sources indicate that the raid caused little material damage, but it marked the beginning of a day of intense aerial activity over the battlefield.
At the same time, French artillery opened fire. The heavy mobile land-navy battery near Breskens joined the battle with its far reaching 155 mm guns, supported by the divisional artillery around Middelburg - two battalions from 89e RA and 307e RAP, both equipped with the famous but ageing soixante-quinze (75 mm) field guns. Allied naval vessels also joined the bombardment, directing fire against German positions on the eastern slopes of the Sloe.
At approximately 0900 hours, German artillery replied. The 10.5 cm howitzers positioned near Lewedorp opened fire on the western bank of the Sloe and the western end of the causeway. The barrage lasted exactly thirty minutes. Shortly thereafter, the entire 9th Company of SS Regiment Deutschland, commanded by SS-Obersturmführer Rhode, advanced across the Sloedam.
The assault immediately encountered fierce resistance. French artillery and the available Allied naval forces concentrated their fire on the advancing Germans. For the first time during the Zeeland campaign, a German attack was decisively checked. The assault stalled almost at once. Elements of the 9th Company became isolated near the French positions and were forced to dig in, where they would endure a miserable day under fire. The remainder of the company, together with the following 10th Company, withdrew after suffering heavy casualties. By day's end, the 9th Company had lost twelve men killed, while several dozen others were wounded. Obersturmführer (1st Lieutenant) Rhode himself was seriously injured.
The successful repulse of the attack greatly encouraged the French defenders. Their celebration, however, was brief. The Germans responded with a massive effort to crush the Allied positions.
Urgent requests for air support were sent to the rear. Throughout the remainder of the morning, German artillery pounded the western bank of the Sloe while He-111 and Ju-88 bombers of KG 4 attacked targets across eastern Walcheren. French artillery positions around Middelburg received particular attention. German aircraft also struck identified targets near Arnemuiden, Flushing, Kapelle and Veere. The skies became crowded with German bombers and fighters, yet not a single Allied fighter appeared to challenge them. Ground-based anti-aircraft defences were weak and sparse, allowing German pilots ample opportunity to identify and attack their targets with considerable accuracy.
Around midday, a second German attack was launched, apparently intended to probe the effects of the aerial and artillery bombardment. It too stalled under French defensive fire. Nevertheless, at roughly the same time, General Deslaurens instructed his staff to begin preparations for the evacuation of Walcheren.
The Dutch offered additional troops to reinforce the rear defensive positions, but Deslaurens declined the proposal. He maintained that the situation remained under control. It is not unreasonable to assume that he regarded Dutch reinforcements as more of a burden than a meaningful contribution. Having witnessed the performance of many Dutch units during the preceding days, he was unlikely to have been impressed. Even so, Deslaurens remained notably courteous toward his Dutch allies, unlike some of his fellow officers.
Further evidence of his apparent lack of confidence in Dutch troops emerged that same day. The only Dutch formation assigned a role in the Sloe defences - the 14th Reserve Border Infantry Company - had been tasked with guarding the shoreline between the Sloedam and Flushing against possible German crossings. When the German artillery barrage shifted toward their sector, the company commander immediately ordered a withdrawal, despite the fact that his unit had not suffered a single casualty. The company eventually fell back to the outskirts of Flushing. Only the 4th Section remained at its post and would not withdraw until German forces had actually broken through at the Sloedam.
Meanwhile, German shelling intensified. Ju 88 dive-bombers of KG 30 joined the attack, concentrating on French artillery positions and preparing the way for another assault across the Sloe.
At the same time, artillery rounds continued to fall not only on the Sloedam but also on Middelburg and its outskirts. Some of this fire on the city may initially have been intended as ranging shots. However, when the French withdrawal began around 1500 hours, French artillery fire appears to have been deliberately directed at the city itself. Although never particularly intense, shells continued to strike the centre and south-eastern districts throughout the afternoon.
Many of these rounds were later assessed as having approached from the south, suggesting a French rather than a German origin. Contribution by the French heavy navy artillery of 155 mm Schneider guns was proven. Part of Middelburg was constructed of light, largely wooden houses. These were obviously vulnerable and easily set ablaze. Fires began to break out across the city. The local fire brigade, equipped with only a handful of engines and wholly unprepared for such conditions, struggled to contain the growing number of blazes. When damage to the water system caused pressure to collapse, the situation became hopeless.
Yet the firefighters continued their efforts despite the shelling. Several were wounded, and a few lost their lives, but they remained at their posts, battling what would soon become a devastating inferno engulfing the historic heart of Middelburg.
At 1800 hours, the Germans launched their third attempt of the day to force the Sloedam. This time, however, the assault was a fully coordinated combined-arms operation. As the infantry advanced along the causeway, German artillery provided close and continuous support, concentrating its fire directly on the French positions at the western end of the dam. Overhead, the aircraft of the Luftwaffe circled relentlessly, diving on any gun position that revealed itself with so much as a muzzle flash.
General Deslaurens, a capable and courageous commander, remained at the front with his men throughout the battle. He witnessed first-hand the effect of the relentless German bombardment. Two or three German artillery batteries maintained a creeping barrage that advanced methodically across the French defensive positions. As the assault troops of 10th Company, SS Regiment Deutschland - which had relieved the heavily battered 9th Company - approached the western end of the causeway, the barrage moved forward once more.
A number of French soldiers managed to bring their rifles to bear on the advancing Germans. Yet when the SS troops surged forward in a determined assault, shouting at the top of their lungs while unleashing a storm of machine-gun fire and hand grenades, the remaining defenders broke. Some fled, while others sought shelter in their foxholes. Organised resistance at the Sloedam collapsed.
The Germans had secured the causeway. With its fall, the fate of Walcheren was effectively sealed. The landscape around the Sloedam and its defences showed that the battle had been tough. Devastation was all around, abondened French wagons, weapons and other material was seen all over the scene. Dead horses and personnel among it.
Despite the intensity of the fighting - and particularly the heavy artillery support and overwhelming German air activity - the casualty figures remained surprisingly modest. The SS Regiment lost approximately twenty-five men killed during the entire operation. Roughly half of these casualties were suffered during the morning attacks, with the remainder incurred during the final assault and subsequent fighting. All in all the German losses KIA and WIA were around 100 men, which is modest for the kind of operation they undertook.
French losses were somewhat higher, although precise figures are not known. The relatively low casualty rate among the defenders can largely be explained by the fact that many positions had already been abandoned before the decisive German attack. When French staff officer Captain Bichon inspected the front line shortly before the final assault, he reportedly found neither officers nor more than a handful of soldiers remaining in the forward positions.
Once the Germans had gained the western end of the causeway, the leading SS elements immediately pressed forward. The remainder of the 3rd Battalion quickly crossed the Sloedam behind them and fanned out toward the south and west. Advancing rapidly, the SS entered Arnemuiden at approximately 1900 hours. The last organised defensive positions disintegrated, and the remaining resistance on Walcheren collapsed.
With the capture of the Sloedam and the fall of Arnemuiden, the island lay open to the German final advance. The final chapter of the campaign in Walcheren had begun. The Sloedam would once again form the scene of a heavy battle when German forces were defending it against attacking British-Canadian forces in 1944. That battle - 'Walcheren causeway' - would last for no less than three days, from 31 October up to and including 2 November 1944.