The 'Battle of the Afsluitdijk' was a small battle fought between German and Dutch forces as the Germans attempted to take the Afsluitdijk (enclosure dike) during their 'Gelb' invasion of the Netherlands (12/14 May 1940).

The German invasion plans called for a simultaneous attack on the 'Vesting Holland' from multiple directions with the expectation of capturing the Hague, capital of the Netherlands, and most important region as it included Amsterdam and Rotterdam, in just one day. To facilitate an attack from the north, German forces commanded by Generalmajor Kurt Feldt, commander of the 1^st Kavalleriedivision of General Georg von Küchler’s 18^th Army within Generaloberst Fedor von Bock’s Heeresgruppe 'B' first needed to cross the Afsluitdijk, a causeway and dike 20 miles (32 km) long and connecting the Netherlands' northern provinces to its western province of North Holland and ultimately to Amsterdam and beyond.

Despite finding themselves outmanned and outgunned, Dutch troops commanded by Kapitein Christiaan Boers managed to hold back the attack at Fort Kornwerderzand, which was protected by modernised and heavily fortified defensive positions. The Germans were thus prevented from immediately concentrating their full strength on the country’s most vital area. Pinned, the German forces were eventually forced to retreat and subsequently directed their attack across the IJsselmeer, bypassing the Afsluitdijk and landing to the north of Amsterdam. Here the Dutch garrison capitulated on 14 May after the 'terror bombing' of Rotterdam. Fort Kornwerderzand was the only line of defence that withstood a German attack during the conflict, and was one of the few 'Blitzkrieg' defeats suffered by the Germans.

The Germans invaded the Netherlands on 10 May 1940 as part of 'Gelb', simultaneously invading Belgium, Luxembourg and France, the last through the Ardennes in 'Sichelschnitt'. In the north, the German forces advanced rapidly past two thin Dutch defensive lines parallel with the border, stretching across the provinces of Drenthe and Groningen, before advancing farther into western Friesland.

On 12 May, the 1^st Kavalleriedivision, which was revised into the 24^th Panzerdivision in November 1941, captured the last line of Dutch defences lying in front of the Afsluitdijk, and began preparing an assault on two defensive lines comprising 17 pillboxes and casemates around Fort Kornwerderzand, designed to withstand direct hits by 210-mm (8.27-in) shells and indirect hits by 280-mm (11.02-in) shells. The fort’s three main casemates were made of 3 m (9.8 ft) of reinforced concrete and accommodated 230 men, 21 7.92-mm (0.312-in) Schwarzlose machine guns, three 50-mm guns, and a 50-mm shore-based naval gun, with similar defences at the Afsluitdijk’s other end.

Earlier in May 1940, two infantry sections totalling 70 men had been despatched to the end of the dike to prevent German landings beyond the vision of both fortresses. The Germans soon discovered these units, and seven Luftwaffe warplanes strafed the Dutch positions. One soldier and two civilians were killed, and 10 civilians were also wounded. The Dutch were forced to retreat to Fort Kornwerderzand.

The German forces did not attempt to take Fort Kornwerderzand until 12 May whe, during the evening, three soldiers were sent to check whether or not the fort had been abandoned. The German reconnaissance patrol was suddenly met by machine gun fire which killed two of the men, but the third escaped. The Germans now decided to take the fortress, planned to call in Luftwaffe attacks, and began an extended howitzer barrage, after which 500 soldiers would commence the assault.

Unknown to the Germans, however, three 20-mm anti-aircraft cannon and four heavy anti-aircraft machine guns had reached Fort Kornwerderzand during the night and, on the following day, pilots who had previously flown unchallenged were met by heavy fire. The Germans sent 62 aircraft to bomb the fort, dropping five waves of bombs. Four aircraft were shot down and crashed into the water. The bombardment was followed by an hour of intense howitzer fire which had little effect on the heavily protected Dutch fortifications.

As soon as the bombardement stopped, German shock troops advanced down the narrow dike on bicycles. Boers, the Dutch commander, waited until the German were within 880 yards (800 m) before he ordered machine gun fire, making it difficult for the Germans to withdraw. Most soldiers tried to take cover, while a few managed to maintain the advance. The Germans were under constant fire for nearly 90 minutes. Once Boers had ordered a ceasefire, the remaining Germans withdrew and the initial assault had clearly failed. During the night Boers ordered the dike to be illuminated by flares and searchlights to warn of any German attempt at a surprise attack.

Early in morning of 14 May, the Germans once again engaged the Dutch fortress with artillery fire, but during the night the Dutch had called in the gunboat Johan Maurits van Nassau, which was now in position to respond with her three 150-mm (5.91-in) guns from her position in the Wadden Sea about 11.2 miles (18 km) from the German positions. Target co-ordinates were provided by telephone from the fortress to the Dutch naval headquarters in Den Helder, then forwarded to the gunboat. This barrage silenced the German guns in less than one hour and shocked Feldt, who was unaware of the presence of any Dutch artillery in the area, let alone guns of so heavy a calibre.

The fortress remained in Dutch hands until the surrender of the Netherlands on 15 May. Boers commended his men by stating that although they had fought like lions, in other parts of the country the Dutch forces had been defeated. Boers himself led the surrender.

Rumours quickly emerged among civilian population, these suggesting that hundreds of Germans had been killed, and that the dike was full of bodies. The German report stated two men had been killed on 12 May and three more on the following day, and about 25 wounded. The Dutch suffered one man killed in the course of the first Luftwaffe attack. Two more men had been wounded while manning anti-aircraft guns. Two civilians were killed and 10 wounded in the German air attack.