Bomvrij militair object, De Bilt

English translation

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Description

Cluster 31. Three concrete blocks of cupola casemates type G.

NEW HOLLANDSE WATERLINIE

Introduction

THREE CONCRETE BLOCKS OF CUPOLA CASEMATES TYPE G are examples of 20th-century, series-built additions to the existing defence. In 1936, the so-called cast-steel cupola casemate was introduced in the Netherlands as a supplement to the existing reinforced concrete casemate, which was based on a system already applied in France in 1917. The armour cupolas used were small in size (favourable with regard to visibility and hit probability), round in shape (favourable with regard to deflecting hits and strength), relatively simple to produce in series, and they had an 'external' firing aperture (favourable with regard to gases and sound). Moreover, they could be manufactured in the Netherlands, which significantly reduced dependence on foreign countries. A first order of 100 pieces in the Netherlands (at DEMKA) was followed by a second of 50 pieces with the Belgian Soc. Anonyme John Cockerill. In total, more than 700 must have been cast in a short time, but only a few remain. The cast-steel cupolas, with a diameter of 1.75 m and thicknesses of 10-17 centimetres, were installed in multiple casemate types with resistance classes W 12-15 to W 21-28.

Shortly before the start of the Second World War, so-called Cast-Steel Cupola Casemates Type G were built in various places in the Dutch lines, notably in the IJssel line, the Maas line, the Grebbe line (each approximately 150) and the New Hollandse Waterlinie (approximately 80 in a reinforced version with a wall thickness of 14 cm). The usual construction of reinforced concrete with one or more fixed firing apertures was abandoned in favour of a system that, within variable limits (up to 270°), could project a line of fire within a cast-steel cylinder with cupola roof. Most cupolas were placed in the Cupola Casemates Type G. Cast-Steel Cupola Casemates Type G were built according to a standardised design and consist of a cast-steel cupola (usually removed), which is anchored in a reinforced concrete structure. On the front side there was a firing aperture with a cantilever section - an 'eyebrow' for protection of the weapon - and on the other side an entrance closable by a steel door. The concrete structure consists of a relatively low rectangular building, with a bevelled section on the front side, to achieve maximum firing field. The standard armament for cupola casemates in the New Hollandse Waterlinie consisted of a heavy machine gun. The firing aperture and the entrance to the casemate could be sealed 'gas-tight' from within. During the Second World War, the vast majority of cupolas inland were demolished by the occupier - partly by blowing them up - to be recast for other steel needs. At the coast they were partly incorporated into the defence, but were mostly demolished after the war. As a result, complete cupola casemates are rare, but they are still found, among others, at the Fort bij Vechten. The concrete structures in which they were placed are found more frequently - but usually in damaged form.

The specimens within the Fort Ruigenhoek complex are located in the eastern and north-eastern main rampart. The specimens are not accessible.

Description

THREE CONCRETE BLOCKS OF CUPOLA CASEMATES TYPE G (1939-1940) at Fort Ruigenhoek, as components of linear and access defence with trench systems, group shelters and the like. The concrete blocks of the three Cupola Casemates Type G are remnants of relatively low, almost square, concrete casemates (approximately 7.00 x 6.20 x 2.50 m; w x d x h), with at the level of the space hollowed out in the front for the cupola, a rearward-sloping surface intended to promote deflection of enemy hits. At the rear a rectangular recess in the concrete to access the cupola. The specimens have been blown up and, as a result, show severe concrete damage; the cupolas have been removed and recast.

Valuation

The THREE CONCRETE BLOCKS OF CUPOLA CASEMATES TYPE G within Fort Ruigenhoek are of general importance because of:

* Cultural-historical values, as part of the New Hollandse Waterlinie as designed by C.R.T. Kraijenhoff and in its initial construction from 1815 by him, Jan Blanken and Major-Engineer Willem Offerhaus, and subsequently strengthened and improved by others over approximately 125 years.

* Architectural-historical values, in particular as an expression of military-strategic architecture, based on: a. the system of inundation and access defence (19th and 20th centuries), b. the race with increasing offensive means (19th and 20th centuries), c. the system of 'living' field fortification in depth (20th century).

These are components from the period 1939-1940. The components are examples of remnants of reinforced concrete casemates, currently without cast-steel cupola.

* Ensemble value and situational values as part of the New Hollandse Waterlinie. Also because of the functional and physical coherence with the other components of the complex, in particular with some group shelters.

* The components are representative (characteristic) because they are clearly recognisable as part of a deconcentrated defence line - but on a fort - added to the existing defence system.

* The components are moderately well preserved, but despite wilful, partial dismantling, they are still clearly recognisable in the field as built objects.