On 17 April 1945, the retreating German occupying forces inundated the polder of Wieringermeer, the Netherlands. Preparations In 1945 German forces occupying the Netherlands planned to destroy the Zuiderzee Works to cover their retreat. Military reasons for this are still unclear, but it may have been done to deny the Allies a landing area for airborne troops or gliders. In preparation for this flooding, the water level of the IJsselmeer was deliberately raised. The level in the IJsselmeer was above the ground level of Wieringerpolder at the site of the breach, and varied between above, across the polder. Inundation had already been used on some Dutch polders but this strategic inundation was shallow and was done by stopping the drainage pumping or allowing water to flow backwards through the pumping stations to give a shallow flooding. The rapid and deep tactical inundation planned for the Wieringerpolder, done by the destruction of a dyke, was new. It was known that even an explosive breach would not be enough, and it would be the enlargement of the breach by the water itself which would cause the most damage. In late February or early March 1945 Dutch workers started to undermine the dike around the polder under German command. The location is near the farm of Beetstra, in the dike with the IJsselmeer. Deep holes were dug in the dike both at the bottom and at the top of the dike. In these holes explosives would be put. The work was progressing slowly since none of the workers were motivated. In April, the work came to a complete stop. On April 10, German officers came and inspected the work. New workers were sought and 25 to 50 people were taken from Schagen during a razzia to work on the digging. After a week, the holes were deep enough and explosives were installed. Each hole was loaded with of explosives; unexploded bombs from British and American aircraft were used. Flooding On 17 April at 12.15 am, the explosives were detonated. The 7,000 people in the Wieringermeer and an estimated 1,000 to 2,000 refugees had to leave the polder. Within 48 hours, the entire polder was full with water, with an average depth of The initial breaches were small, about wide and only below water level. These increased over the following hours until two huge pits were scoured out, the northern one wide and deep