German invasion of the Netherlands
This new position was called the New Holland Water Line. The line was given new pillboxes in 1940. The line was below sea level. This allowed it to be flooded with a few feet of water. This was too shallow for boats, but deep enough to turn the soil into mud. The area west of the New Holland Water Line was called Fortress Holland (Dutch: Vesting Holland; German: Festung Holland). The eastern side was covered by Lake IJssel and the southern side protected by three rivers. It was expected to hold out for a long period of time.