When the Dutch built their defence lines hundreds of years ago, they built them with the expectation that the enemy comes from the east. So they built a dyke on the edge where the high ground met the low, so the low ground could be flooded. This had worked well all through the centuries, even as late as 1940.
When Hitler's armies came, they had expected to just walk through it. Of course they knew about this formidable obstruction, so they figured they would go around it.
When there was too much resistance (see GREBBEBERG), he ordered the bombing of the open city of Rotterdam. Four years later, when the tide had turned from offender to defender, they took another look at the dyke that so successfully repelled them back then. However, this time the flooding would do no good, because the enemy would come from the west. However, the dyke would still be useful as a defence line with some modifications. So they went to work building bunkers, not little things like the Dutch, no big ones with one meter thick concrete walls, and of course facing west, not east as that was where their homeland was.
Now who was gonna build them? Only one way, the soldiers themselves, for at least three reasons. First, there were no more civilian contractors able to build anything, no more workers and no more machinery or material. Second, kept the Dutch out as they would sabotage and spy, and third, kept the army busy, the soldiers occupied and gave them a goal to fulfil, so they didn't think too much for themselves and became demoralized.
But oh, what a disaster. How demoralized could a person become? After all this work of building the bunkers facing west, the allies were coming from the east. Would not that make your hair stand up on your neck, or cause you to kick your dog in frustration?
Too late to inundate the place, the Dutch bunkers had been torn down. No more natural cooperation; instead of a defence line, it had become more of a trap line.
We wondered later on, if the underground had helped in some way to make up the mind of high command to go the way they went. We sure hope we did. I knew it was bothersome for the Germans, because I saw them cruising around, trying to find where the secret senders where hidden. They had antennas sticking through the roof of a vehicle. They stopped for a while, turned the antenna, went a little distance and repeated this action. If they found any, I never heard.
The Zuiderzee and Delta Works of the Netherlands. "The second polder, the Noordoostpolder, was started in 1936 and draining it wasn't finished until 1942. The area turned out to be a good resource for the Dutch Underground resistance in World War II as it provided almost 230 square miles of undeveloped land to hide from the Nazi occupation force.
World War II also brought some setbacks to the project, however. In April 1945, the retreating German forces blew up the dike of the Wieringermeer, flooding the land again. Fortunately the Dutch managed to reclaim the polder by the end of the year, though much of the infrastructure was destroyed and had to be rebuilt."
Sweet and Salt: Water and the Dutch by J. Green. "The Dutch have been 'building in their soggy little delta since they settled there.' Dyke building has always been an intensive process. Instead of adding landfill and pushing water out with new land forms, the Dutch have actually been pumping water out ...
Through World War II and after, the system of dykes the Dutch relied on had received little maintenance. As a result, in 1953, dykes burst in 50 different places at once. The result is that 1,835 people + 1 died. The '+1' is the young, unnamed child who drowned in her mother's arms along with her mother. There are memorials everywhere to them. Some 700,000 people lost their homes and more than 1 million animals died. The Dutch vowed never again. Their answer to the flooding was 'hard, concrete solutions.'"