German invasion plans called for a simultaneous attack on Vesting Holland from multiple directions, expecting to capture the country's capital and most important region in a day's time.

Despite finding themselves outmanned and outgunned, Royal Dutch Army troops commanded by Captain Christiaan Boers, under the overall command of rear-Admiral Hoyte Jolles, managed to successfully hold back the attackers at Fort Kornwerderzand, protected by modernized heavily fortified defensive positions.

Kornwerderzand was the only line of defense that successfully withstood an enemy attack during the conflict, and was one of the few Blitzkrieg defeats suffered by the Wehrmacht.

On 12 May, the German 1st Cavalry Division—later regrouped into the 24th Panzer Division—had 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 rounds and indirect hits by 280 mm rounds.

The Germans nevertheless decided to take the fortress and planned to call in Luftwaffe strikes, before firing an extended howitzer barrage, after which 500 soldiers would commence the assault.

[3] The Dutch commander, Christiaan Boers, waited until they were within 800 metres (870 yd) before he ordered machine-gun fire, making it difficult for the Germans to withdraw.

On the early morning of 14 May, the Germans once again fired their artillery at the fortress, but during the night Rear-Admiral Jolles had ordered the gunboat HNLMS Johan Maurits van Nassau, which returned fire with her three heavy 150 mm guns from her position in the Wadden Sea; approximately 18 kilometres (11 mi) from the German positions.

This barrage silenced the German guns in less than an hour and shocked General Kurt Feldt, who was unaware of the presence of any Dutch artillery in the area, let alone such a heavy caliber.