This strange construction is located at the Machinekade, a dike east of Maarssen. In fact it is a combination of two standard infantry shelter built against each other. When the Dutch troops occupied the New Water Line in the autumn of 1939 the forts were not very suitable for modern warfare. To improve the line the Army staff decided to construct a large number of shelters on the forts, but also between them. Each shelter could house a group of 13 men, but also a command post.

Since the terrain of the New Water Line is rather soft, quite would became even worse during the inundations all the shelters had to be constructed on piles. Because the shelters had to resist hits of heavy shells coming from different directions the piles were driven into the ground under different angles.