Luchtwachttoren 5K3 in Strijensas, Netherlands

Along the windswept dike of the Mariapolder, overlooking the broad waters of the Hollands Diep, stands a curious concrete relic of Dutch military vigilance: Luchtwachttoren 5K3, the lowest surviving Cold War-era air watchtower in the Netherlands. But beneath its modest stature lies a unique palimpsest of layered defenses — a rare fusion of Dutch water engineering and mid-20th-century military architecture. Built around 1953, 5K3 wasn’t constructed from scratch but ingeniously placed on top of an existing 1937 VIS-kazemat, a type of pre-WWII Dutch pillbox. Both structures sit directly on the Oude Dijk, itself a vital flood barrier — making this site a literal stacking of defense lines: water, land, and sky. The tower was part of a nationwide observation network of 276 posts constructed during the early Cold War by the Korps Luchtwachtdienst (KLD). This volunteer force was tasked with spotting low-flying Soviet aircraft—something contemporary radar systems of the 1950s couldn’t reliably do. Constructed from prefabricated concrete elements, these towers featured open-air observation platforms with angular grid tables for triangulating aircraft positions using simple optics. Tower 5K3, like its taller siblings, was both spartan and strategic. Volunteers would climb wooden stairs and steel ladders to the top platform, stand exposed to the elements, and scan the skies with binoculars—ready to raise the alarm in case of an air threat. Ironically, the full network never engaged in active wartime defense, although in 1958, one post reportedly identified a Soviet aircraft off-course over Dutch airspace. After the KLD disbanded in 1968 and many towers were demolished, only 19 remain. Tower 5K3 is one of the few still standing, now silent but powerfully evocative — a concrete watchman over the water, preserving a little-known chapter of Cold War paranoia and Dutch defensive ingenuity.