The three-man 'porcupine' bunker served to counter the German threat. Dozens of concrete casemates were built between Maastricht and Echt in 1939 and 1940. They were part of the Juliana Canal Line, which formed part of the Meuse Line.
Three soldiers manned the casemate: two operated the machine gun and the third stood guard and provided ventilation to dispel the gunpowder fumes. The bunker at Elsloo is the only one still standing. The others were demolished in the 1950s and 1960s. Today, the 'porcupine' has become an accommodation for bats.