The watchers of times gone by
We had thought we would escape it; that we would be the generation that would never experience war. But we’re no longer so sure about that. Circumstances can change in such a way that—what once seemed impossible—could suddenly become reality. Of course, we hope it won’t happen; we hope we can keep war outside our door. That’s what the Netherlands wanted too after World War II. That war ended in 1945 and the world began to recover. But a situation arose where we could no longer fully count on lasting peace: the Cold War.
The Cold War was a period of armed peace during the second half of the 20th century. Communists on one side—mainly the Soviet Union and China—and capitalists on the other side, separated by the Iron Curtain. The term ‘Cold War’ seemed to be coined by writer and journalist George Orwell, who used it in a 1945 article in The Tribune. That same year, his book ‘Animal Farm’ was published. The story is about a commune of intelligent farm animals who want to overthrow their tyrannical master so they can work and live as equals. That is unsuccessful, and eventually the commune became a dictatorship. The comparison to the Soviet Union and life under Stalin was quickly made. The fear of a new world war during the Cold War era was fuelled by the Korean War (1950), the Hungarian Uprising (1956), the construction of the Berlin Wall (1961), and the Cuban Missile Crisis (1962). One of the responses to this was the founding of NATO in 1949.
What few people know is that there are still remnants of the Cold War to be found in the Netherlands. In the landscape of this country, we are familiar with the remains of forts such as those of the Hollandic Water Line. The line was built to protect Holland and Utrecht, and the forts were in use from 1870 to 1945. These forts are often protected as monuments and have largely been restored. The remnants of the Cold War, however, often are not, and in some cases are barely recognisable. We are talking about the so-called air watchtowers, the military lookout towers. There were nearly 300 of them in the Netherlands. With a bit of effort, you can still find at least 21. Some are so unrecognisable today that they are virtually impossible to find.
NATO member states increasingly coordinated their national air defense systems. Between 1947 and 1949, the Ministry of War prepared the establishment of a new national air watch service. The Dutch Air Watch Service Corps (KLD) was established in 1950 and operated under the command of the Royal Netherlands Air Force. The KLD was tasked with the observation and reporting of enemy aircraft that had penetrated national airspace, especially from the Soviet Union. The radar system could not detect low-flying aircraft below 1,500 meters—something had to be done about that. This became a network of air watchtowers across the entire country, divided into 8 sectors, 80 air watch circles with 276 posts. Each sector had an air watch center. The air watch center filtered the incoming reports and passed them on to the air defence headquarters in Driebergen (from 1952 onwards). The numbers of air watch centers and posts were based on the number of flights an air watch centre could handle simultaneously during high air activity in wartime, and on the capacity of the civilian and military telephone network. They had to be permanent structures, and posts on existing buildings were also considered. This resulted in a triangular structure projected on the map of the Netherlands, in which three air watchtowers were always located within a maximum of 16 km apart. Eight air watch centres were designated. Each tower received a post name consisting of a number, a letter, and another number. The first digit of the post name referred to the relevant air watch centres.
The air watchtowers were built between 1951 and 1958. Half of the air watchtowers could be built on existing buildings, such as mills or factory buildings. Not that the building owners were particularly eager to allow it, by the way. Many owners refused to cooperate due to the increased risk of danger to utilities or drinking water supplies, or personnel. To ensure that the towers themselves didn’t need to be built too high, locations that were already elevated—such as dunes and natural hilltops—were chosen.
A total of 144 freestanding towers were built (145 if a relocated tower is included). A separate design was made for these towers. The first design, from the Bureau of Buildings and Airfields in 1950, consisted of a wooden air watch post on a concrete platform. Wood was ultimately rejected as a building material: it was too costly to maintain, posed a fire risk from lightning strikes, and swayed too much when used for tall towers. The commission for a standard design was given to the firm Schokbeton, which worked with architect and structural engineer Marten Zwaagstra (1895–1988) on a prefabrication system previously used in housing construction. He was both an architect and entrepreneur. In 1920, he earned his diploma in architecture and in reinforced concrete construction from the technical school in Leeuwarden. In the 1950s, he founded the company N.V. Raatbouw. Especially for the air watchtowers, he designed prefab elements made of shock-resistant concrete in the shape of honeycomb elements—hence the name ‘raat’ which is a honeycomb in Dutch.
A quick detour to talk about ‘shock concrete,’ since it’s a Dutch invention—and after all, Jan and I are architectural engineers. The developer of shock concrete, Gerrit Lieve, made his discovery when he was transporting a load of concrete in a wheelbarrow with a broken wheel. He noticed that his load had already hardened upon arrival and wondered why. He then tested the principle of this process by experimenting with a wheelbarrow whose wheel he had modified by tying a rope full of knots around it. He rolled it over a plank while a small amount of mortar was in the tub. Mortar is a moist, non-liquid mixture of sand, cement, and fine gravel with a small amount of water. He later adapted this process for concrete in factory molds. By ‘shocking’ the mold with the concrete inside, the material becomes more compacted, after which it continues to harden chemically. In 1932, he filed a patent for the idea of concrete compaction through shaking. That same year, Gerrit Lieve and his partner M.E. Leeuwrik founded the company N.V. Schokbeton in Kampen, with a production facility in Zwijndrecht. The most well-known structures made from shock concrete in the Netherlands are around 900 prefab barns, particularly visible in the Noordoostpolder, and the air watchtowers.
The system that Marten Zwaagstra developed for the air watchtowers consisted of building blocks measuring 38cm2. The dimensions of the towers were based on this. The idea was that the air watchtowers would only be in use for a limited time, so it made sense if their materials could be reused. The open honeycomb beams with reinforcing steel were often seven cells long. Vertically, the beams were bolted together. Using special corner elements, towers were built with load-bearing walls that were inherently stable and rigid. Platforms were placed using honeycomb beams, onto which wooden stairs were mounted. The platforms and the lower part of the facade were enclosed (the latter to prevent the towers from being easily climbed) with special tiles that clicked into the beams and locked together. By using an open structure, material and weight were saved, and the tower was also less sensitive to wind. At the top of the tower was an open observation platform measuring 3m2, protected by a 1.5m high parapet. Many towers were also equipped with a shelter niche on top. The platform was wider than the base, meaning the tower widened toward the top.
You’re probably wondering how the aircrafts were actually spotted—because that’s what the towers were for. Men worked three-hour shifts—women were not allowed—and stood or sat in pairs on the observation platform with binoculars, a map of the area, an air watch instrument, headphones, and a sheet showing aircraft from the Soviet Union. The men were volunteers between the ages of 16 and 60. Each tower had 16 volunteers. That means a total of about 3.700 personnel were needed to cover the entire country. The task of the KLD was described as follows: “to identify enemy aircraft through observation and listening posts and to provide information needed to counter enemy air attacks and to warn one’s own troops and the civilian population in time of aerial threats.” The volunteers had to be able to quickly reach a nearby village by bicycle; this determined the locations of the towers. From there, they would contact the air watch centres.
What did the watchers on the towers actually spot? In truth, nothing more than passing birds—for about ten years. With one exception: in 1958, two observation posts near Montfort in Limburg spotted a Russian Ilyushin. The aircraft had participated in a French airshow and, on its return flight, had veered off course to photograph the border area. This was reported to the Germans, who forced the plane to land in Düsseldorf. To be fair, by the time the air watch towers had been completed, the aviation industry had already transitioned from propeller to jet aircraft. Radar technology had also advanced significantly. You also must wonder whether any warnings would have reached the public in time—after all, the volunteer first had to bike to a village, then make a phone call to the air watch centre, and only then wait for follow-up actions. I immediately get a mental image of the British comedy series ‘Dad’s Army’ from the late 1960s—and I can’t help but chuckle.
Today, only 21 remnants of these remarkable structures remain. One of those towers caught our eye at the end of 2003: post 7O1 on the Baron van Asbeckweg between (part of the village now called Wehe den Hoorn). We had a second home in the Hogeland region and regularly passed this tower on our way. It had something mysterious about it—the overgrowth blocked the view of the base. All you could see was a concrete structure rising above the trees. In 2013, Jan made a watercolour painting of it. A structure like that continues to captivate you.
In early 2017, news came out that the air watch tower was going to be restored. A crowdfunding campaign was even launched for the project, to which we contributed. The restoration was carried out between March and July 2017 by Holstein Restoration Architecture. An article about it was published in ‘Bouwwereld’magazine in January 2018. The restoration of the tower was commissioned by the Groninger Landscape Foundation. The condition of the tower was not bad, but five new honeycomb beams and 300 new tiles had to be made. 250 bolts were replaced, and the rest were preserved. Concrete repairs were carried out, after which the tower was treated with a water-repellent coating (a kind of impregnation) to prevent water intrusion, reinforcement corrosion, and frost damage. Two people from the construction company in Groningen worked for seven weeks to restore the tower. This air watchtower has its own foundation that manages it and provides guides for tours. One last note about the crowdfunding: one of the perks was that you received a vertically placed tile in the tower bearing your name. The keen observer can find one with Jan’s name on it!
Once you’ve seen one of those air watchtowers, you start investigating to find out if there are more. And nowadays, it’s much easier to do so. There’s a Dutch website that lists the air watch towers, complete with a map and detailed information for each one. During a visit to the Verbeke Foundation in Stekene (Belgium), we came across a photo book by photographer Herman van den Boom titled ‘Air Watch Towers in the Netherlands, the Artwork as Artwork’ (2021). He was intrigued by tower 8J2 in Maashees and began searching for more towers. Herman speaks of 17 remaining air watch towers, though there are actually more. Admittedly, they’re not always easy to recognise as such. But since 2022, you can find everything there is to know about these towers in the comprehensive book ‘Air Watchtowers from the Cold War’ by Sandra van Lochem. And ‘comprehensive’ is no exaggeration: 400 pages with 650 images. We obviously can’t—and don’t want to—compete with that!
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What we do want is to give you a small glimpse into what remains of the air watchtowers in the Netherlands. Let’s start by mentioning that there are two air watchtowers that were not built using shock concrete and honeycomb beams. These are towers 5C1 in and 5D1 in . Starting with the latter: it looks more like a short lighthouse. The standard tower design didn’t appeal to the municipality, so a different design was created. It’s a slender square brick tower, 11.9m tall, built in the style of the Delft School. The tower narrows as it rises and then flares out again at the platform level. Construction was delayed and wasn’t completed until 1958; it was already decommissioned by 1964. In 1969, an apartment complex was built next to it on the edge of the Braassemermeer. Today, the tower is used as the management office for that complex. The tower in Scheveningen is a tapered brick structure, without any architectural detail at the platform, and made from yellow and red bricks. The tower itself is only 6.5m tall but stands on a dune (made from rubble from the 1945 bombing of Bezuidenhout) that is 31m high. Both towers are, by the way, designated as municipal monuments.
There are also two air watch towers that have become unrecognisable. These are tower 5C3 in and 2W2 in . The one in Zoeterwoude used to be 12.02m tall but has been reduced to 2.9m. The lower part of the tower, made from enclosed honeycomb beams, is now used as a small shed. The tower in Kamerik suffered the same fate—though it is even less recognisable due to the small, pitched roof and dormer that have been added to it.
There are still 17 recognisable air watchtowers built with honeycomb beams of shock concrete. It would take us too far to describe all of them in our story. You can find the addresses of all towers, except those that are privately owned in the book. Keep in mind that the surroundings have often changed significantly since the towers were built. It is a fun scavenger hunt that good friends of ours have also done, including our friend the architect Arie van Rangelrooy, who unfortunately passed away too young to finish it. In many cases, the towers are hidden behind trees. We’d like to point out a few special cases. The tallest tower ever was the one in Nieuw-Loosdrecht, with a height of 33.5 m. In the old photo, this tall, slender structure looks extremely fragile. The tallest of the still existing air watchtowers stands in , Zeeland: tower 3T1, 21.05 m tall. The three remaining towers in Zeeland are among the tallest surviving towers. Due to its height and the type of soil, the tower in Koewacht has buttresses at its base for additional support. The second tallest tower, located in (3T3), 16.49 m tall, appears in photos showing poplar trees being planted nearby to make it less noticeable. At a certain point, the tall trees blocked the view of the tower, and in 2008 they were replaced by young trees.
From the tallest to the shortest still-standing tower: 5K3 in North Brabant. This tower, which is 6.32 m high, was built in 1953 on top of an existing bunker. The bunker is a Dutch VIS casemate from 1937 (Directive for Constructing Defensive Positions). It’s of course not surprising to combine such structures. The air watch tower 8E1 in was built on Fort Sint Andries. Today, it’s hard to imagine how such—especially the smaller—towers had to operate.
I can’t help but think again of George Orwell. He was called a participatory journalist at the time. In December 1936, he left for Spain to fight fascism in the Spanish Civil War. He enlisted in the militia of the Marxist Partido Obrero de Unificación Marxista (POUM) and was seriously wounded on May 17, 1937, at the front near Huesca by a gunshot to the neck. While recovering in Barcelona, he witnessed the violent clashes between, on one side, the Stalinist communists and their allies, and on the other, POUM and the anarcho-syndicalistConfederación Nacional del Trabajo (CNT). The Stalinist witch hunt against POUM—with smear campaigns, false accusations, house raids, and arrests—turned him into a lifelong anti-Stalinist. He described his experiences in the autobiographical book ‘Homage to Catalonia’. In November 2023, the booklet ‘Over Nationalisme’ by Bas Heijne was published. He combined his essay ‘How We All Became Nationalists’ with Orwell’s ‘Notes on Nationalism’. The latter was published in Polemic in October 1945. It is—unfortunately—still strikingly relevant. What is our response to today’s threats? Will we find a better solution than the watchers of times long gone by?
2025