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© 1999-2024, René G.A. Ros
Last modified: 7/6/2024 (dmy)

The Defence Line - Usage

Defendable earthworks were the first phase of the building of the Defence Line. The bombproof buildings were later constructed and were used as soon as they were ready. In peacetime, most of the forts were unoccupied, excepting the two coastal forts of IJmuiden and Pampus
The forts sometimes had heavy artillery, but mainly only small calibre guns, as their primary objective was simply the closure of nearby accesses, for example railroads, roads and the larger waterways, through which the enemy could advance more easily than through inundated terrain. The polders could be, within half a day, inundated with 0.2 to 0.3 metres of water; too deep for infantry but to shallow for boats.

To ensure enough water for the inundations, special canals and other such works were built. When all of the building was completed, the Defence Line extended in a 3 to 5 kilometre radius, covering a 150 kilometre circumference and consisted of 42 forts and batteries. The circle of water lay (and still lies) about 10 to 15 kilometres from the centre of Amsterdam. Because of this, the city was at a safe distance from enemy artillery, but not too far away for good transport and communication facilities. The great advantage of a water defence line is that a large area can be defended with relatively little manpower. The inundated areas required only a light defence - the weak spots in the Line were the access points which could be defended more effectively by on-site soldiers. The inundations formed a passive defence. The active defence existed, for instance, in the form of the forts which were positioned a maximum of 3.5 kilometres from each other. However, the real active defence was the mobile artillery. Stationed near the forts when not in use, during the defence this artillery could be placed in the protection of dikes and ramparts between the forts and fire at the enemy from several batteries.
The defenders were more familiar with the inundated area than the attackers and knew exactly where they could sail. This was possible by using covered barges. These covered barges each housed one large piece of artillery.


Soldier in a concrete shelter.
(Picture: Collection Army Museum, Delft, The Netherlands / Jaap de Zee, 1916)

There is not much known about military exercises, mostly due to secrecy. A few large-scale exercises are recorded, the last of these being held in September of 1916. During the large-scale manoeuvres of September 1912, five forts were fitted to war strength. There is a unique report in the "Algemeen Handelsblad" newspaper about this exercise.
Most of the exercises, in the Defence Line and elsewhere, took place during the mobilisation of 1914-1919. The exercises supplied a lot of insight to the military, which had bad preparations, delays because of material shortage and a far from optimal command structure to contend with.

After the Great War the Defence Line formed the north side of the "Vesting Holland" (the "Fortress Holland"). The Nieuwe Hollandse Waterlinie (New Dutch Waterline) formed the East and South sides.

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Defence Line of Amsterdam. A city wall of water.
UNESCO Werelderfgoed sinds 1996
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'Introduction to the Defence Line of Amsterdam' is a interactive ebook about the Defence Line of Amsterdam.