Visit Holland - The Netherlands
The Dutch Water Line (Dutch: Hollandsche Waterlinie) was a series of water based defences conceived by Maurice of Nassau in the early 17th century, and realised by his half brother Frederick Henry.
Combined with natural bodies of water, it could be used to transform the economic heartland of the Dutch Republic almost into an island.
Early in the Eighty Years' War of Independence against Spain the Dutch had realized that flooding low lying areas formed an excellent defence against enemy troops, as was demonstrated, for example, during the siege of Leiden, 1574. In the latter half of the war when the economic heartland of the Dutch Republic (i.e. the province of Holland) had been freed of Spanish troops. Maurice of Orange Nassau planned to protect it with a line of flooded land protected by fortresses that ran from the Zuiderzee (present IJsselmeer) down to the river Waal.
After the final defeat of Napoleon in 1815 at the Battle of Waterloo, the United Kingdom of the Netherlands was formed. Soon after king William I decided to modernise the waterline. The Water Line was partly shifted east of Utrecht.
In the next 100 years the main Dutch defence line would be the new water line which was further extended and modernised in the 19th century with forts containing round gun towers reminiscent of Martello towers. The line was mobilised but never attacked during the Franco-Prussian war in 1870 and World War I.
At the advent of the Second World War most of the earth and brick fortifications in the Water Line were too vulnerable to modern artillery and bombs to withstand a protracted siege. To remedy this a large number of pillboxes were added. However, the Dutch had decided to use a more eastern main defence line, the Grebbe line, and reserved a secondary role for the Water line. When the Grebbe line was broken on May 13, the field army was withdrawn to the Water Line. However, modern warfare could circumvent fixed defense lines (cf. the French Maginot line). While the Dutch army was fighting a fixed battle at the Grebbe line, German airborne troops had captured the southern approaches into the heart of "Fortress Holland" by surprise — the key points being the bridges at Moerdijk, Dordrecht and Rotterdam. When resistance did not cease, the Germans forced the Dutch into surrender by aerial bombing of Rotterdam, and threatening the same for Utrecht and Amsterdam. Therefore, during the Battle of the Netherlands in May 1940 there was no fighting at the line itself.
After the Second World War, the Dutch government redesigned the idea of a waterline to counter a possible Soviet invasion. This third version of the waterline was erected more to the east at the IJssel (the IJssel Line) and in Gelderland. In case of an invasion, the water of the Rhine and the Waal were set to divert into the IJssel, flooding the river and bordering lands. The plan was never tested, and dismantled by the Dutch government in 1963.