By the late afternoon of 17 May, it had become clear that German forces had occupied virtually all of Zeeland, with the exception of the most southern landslide, Zeeuws-Vlaanderen.
Even while the fighting around the Sloedam was still in progress, Dutch units in western Walcheren had already begun inquiring at headquarters whether capitulation might be permitted. Many local commanders, however, found it difficult to establish contact with the Dutch staff, not least because of the ongoing bombardment of Middelburg. As communication broke down, local initiatives to surrender began to emerge.
A controversial role was once again played by Lieutenant-Colonel Themann, commander of the re-concentrated Peel troops and commanding officer of the 30th Infantry Regiment. In the preceding days, he had already demonstrated shortcomings as a leader. When contact with headquarters in Middelburg proved impossible, he reportedly informed fellow officers that, as the senior officer present, he would personally decide on capitulation if necessary.
Although Themann apparently did not intend this remark as an order to surrender, many subordinate commanders interpreted it as evidence that a decision to lay down arms had effectively already been taken. As a senior field commander, greater clarity might have prevented such misunderstandings. In fairness to Themann, it should be noted that many officers and men were already exhausted and demoralized after days of fighting. The prospect of surrender was therefore received with considerable sympathy by some of the troops.
Before long, white flags began appearing at several locations, particularly on church towers and other prominent buildings. When reports of this reached Themann, he was shocked by the misunderstanding and immediately dispatched messengers to the affected locations with orders that the flags be removed.
At Veere, however, one of the towns where a white flag had been hoisted on the church tower, the consequences were unfortunate. A company of French troops was stationed there, and when its soldiers saw the symbol of surrender flying above the town, they felt deeply betrayed by their Dutch allies. In protest and confusion, the Dutch troops temporarily abandoned their positions and marched out of the town. It was not until approximately 1600 hours that they returned.
At 1400 hours, Themann formally instructed all unit commanders that their positions were to be prepared for defence and that capitulation remained out of the question. All white flags were to be removed immediately.
Needless to say, the units receiving these orders displayed little enthusiasm for taking down the flags. Even less enthusiasm remained for continuing the fight against an enemy whose victory now appeared inevitable.
Meanwhile, Lieutenant-Colonel Karel, acting on behalf of the Commander of Zeeland, had contacted his superior in Breskens and requested permission to demolish the four coastal batteries. At Dishoek on Walcheren, the heavy coastal battery had already been destroyed when a counter-order arrived instructing that further demolitions be postponed. The order came too late to save the Dishoek battery, but the remaining batteries were temporarily spared. It will come as little surprise that the eventual order to destroy the remaining batteries was issued too late. In the end, all three would be put to good use by the Germans.
Throughout the day, Van der Stad was repeatedly approached by subordinate officers and by the Mayor of Middelburg, all asking the same question: when would Walcheren's surrender be offered to the Germans? Van der Stad remained adamant that such a step could not be taken as long as French forces were still actively engaged in combat.
His representative, Lieutenant-Colonel Karel, viewed the situation differently. By 1700 hours he had concluded that capitulation was unavoidable. Not only did he hope to spare the lives of his soldiers, but he was also desperate to bring an end to the devastating bombardment of Middelburg. At 1800 hours, Karel ordered all Dutch troops on Walcheren to lay down their arms and display white flags as a sign of surrender.
At 1830 hours, a radio message announced that the Dutch forces on Walcheren and Zuid-Beveland had capitulated. Half an hour later, Lieutenant-Colonel Karel personally travelled east of Middelburg along the road used by the advancing German troops where the Germans intercepted him. He was taken to a hotel near the locks outside Flushing, where he formally informed SS Standartenführer Felix Steiner, commander of the SS regiment, of the surrender of the Dutch forces on Walcheren and Zuid-Beveland.
Noord-Beveland, the small island just north of Walcheren and Zuid-Beveland, was not formally included in the capitulation agreement. However, on the morning of 18 May, a German officer crossed over under a flag of truce and informed the local Dutch commander that the Dutch forces elsewhere in Zeeland had already surrendered. Isolated and cut off from any possibility of further resistance, the Dutch troops on Noord-Beveland likewise laid down their arms.
The SS regiment's mission in Zeeland had effectively come to an end on the evening of 17 May. On the morning of 18 May, it was relieved by a reinforced battalion of the 225th Infantry Division. Only the two artillery battalions of the original task force remained behind to assist in the establishment of coastal defences, mainly positioning to the south. The SS regiment subsequently rejoined its parent division. One day later, it was assigned to General Von Kleist's armoured group, Panzergruppe von Kleist, for the continuation of operations in France.
The battle for Walcheren and Zuid-Beveland had come to an end. Remarkably, it had taken the Germans almost four days to secure the islands. On the German side, the campaign had been conducted primarily by just two reinforced battalions of SS Regiment Deutschland. This relatively small force succeeded in overcoming an opposing force at least three times its size, while suffering only 63 men killed in action. The formations responsible for the capture of Tholen, Sint Philipsland, and Schouwen-Duiveland lost a further nine men killed in action. The entire German death toll had been 72 man KIA, which is very modest in comparison to the benefits.
French losses on the islands are more difficult to determine with certainty. A separate study of French casualties identified 229 French soldiers killed during the campaign in Zeeland, although it can be positively assessed that a number of these losses in fact occurred in western North Brabant rather than on Walcheren and Zuid-Beveland themselves.
Dutch losses were comparatively modest. In the defence of their own territory, 38 Dutch soldiers lost their lives, including five officers. Of these, four were killed during the fighting on Tholen and Schouwen-Duiveland, while five fell victim to incidents related to Fifth Column panic. This leaves only 29 Dutch soldiers killed as a direct result of combat during the entire eight-day campaign in Zeeland. Even more striking is the fact that only 13 of these fatalities occurred during the period of the actual German ground offensive against Walcheren and Zuid-Beveland.
The low number of Dutch casualties reflected both the limited scale of the fighting that it got involved in and the rapid collapse of organized Dutch resistance once the German breakthrough across the Sloedam had been achieved.