Kazemat, Fort bij Tienhoven Tienhoven (Stichtse Vecht 26)

English translation

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Description

Cluster 20. Cast steel dome casemates type G.

NEW HOLLANDIC WATERLINE

Introduction

Two concrete remains of CAST STEEL DOME CASEMATES TYPE G as components of access defence with trench systems, group shelters, obstacles and similar. One specimen lies at the front side of the fort and the other to the southwest of the fort. In 1936, as a supplement to the reinforced concrete casemate, the so-called cast steel dome casemate was introduced in the Netherlands, which was based on a system already applied in France in 1917. The armoured domes used were small in size (favourable with regard to visibility and hit probability), round in shape (favourable with regard to strength and deflecting hits), 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 at the Belgian Soc. Anonyme John Cockerill. In total, over 700 must have been cast in a short time, but only a few of these remain. The cast steel domes, 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 outbreak of the Second World War, Cast Steel Dome Casemates Type G were constructed at various locations in the Dutch lines, particularly in the Yssel line, the Meuse line, the Grebbe line (each approximately 150) and the New Hollandic Waterline (approximately 80). The usual construction of reinforced concrete with one or more fixed gun openings was abandoned in favour of a system that had a firing direction that could be projected within variable limits (up to 270°), within a cast steel cylinder with a dome roof. The dome casemates were standardly equipped with a heavy machine gun as armament. The firing aperture in the dome formed a rounded, rectangular 'eyebrow' of approximately 10 cm thickness, which protruded some decimetres beyond the dome and provided protection for the weapon positioned inside - a heavy machine gun or cannon. Both the firing opening and the access to the casemate, which was located in a recess behind the dome, could be sealed 'gas-tight' from inside. Cast Steel Dome Casemates Type G were, apart from at existing accesses, also applied several times to defend 'new accesses', that is to say at locations where new (motor) roads or (electrified) railways had been planned or realised. The front side of the casemates could be provided with an earth covering and camouflage. During the Second World War, the vast majority of domes in the interior were demolished by the occupier from the casemates - partly by blowing them up - with the aim of melting them down for other steel requirements. On the coast, they were partly incorporated into the defence, but after the war they were often demolished nonetheless. As a result, complete Cast Steel Dome Casemates Type G are rare; they are in any case still found at Fort Vechten. The concrete structures in which they were placed are more commonly found - but due to demolition usually in damaged form. The latter is also the case with the specimens on and around the Fort at Tienhoven.

Description

Remains of CAST STEEL DOME CASEMATES TYPE G are remnants of relatively low, almost square, concrete casemates (approx. 7.00 x 6.50 x 3.00 m; w x d x h), with a surface sloping backwards at the height of the dome recessed in them, onto which any enemy hits could ricochet. At the rear is a recess in the concrete block through which the casemate and dome could be entered. The specimens present as part of the 'complex Fort at Tienhoven' have both been blown up and as a result show severe concrete damage; the domes have been removed and remelted. The casemates still lie reasonably clearly visible in the terrain because they were meant to have a free field of fire in the direction of Nieuweweg.

Valuation

The remains of the CAST STEEL DOME CASEMATES TYPE G at the Fort at Tienhoven are of general importance because of:

* Cultural-historical values as part of the New Hollandic Waterline as designed by C.R.T. Kraijenhoff and initially constructed 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, which is based on: a. the system of inundation and access defence (19th and 20th centuries), b. the race with strengthening offensive means (20th century) c. the system of 'living' field fortification in depth (20th century)

These are components from the period 1936-1940. These components are examples of reinforced concrete casemates (Type G), now without cast steel dome (later removed).

* Ensemble value and situational values as part of the New Hollandic Waterline. Also because of the functional and physical coherence with the other components of the complex and in particular with the access of the Nieuweweg.

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

* The components are moderately well preserved as a result of deliberate damage in the period 1940-1945, but they can still be clearly recognised as built components in the field.