The two southern branches were intended as a delay line. The northern branch followed the Geleen Brook and the southern branch the river Geul. Both tactical lines consisted of a belt of casemates designed to slow down the advancing German troops as much as possible so that there would be time to put the bridges over the river Meuse and the Juliana Canal out of order.

Lieutenant Colonel Albert Govers, the Territorial Commander of South Limburg, was responsible for the construction. The Geul Line had an advanced position: the Border Line that comprised four casemates, including this casemate 1 near Mamelis on the border with Germany. The second line, the actual Delay Line, had 30 casemates. The concrete was barely dry when the Germans invaded on 10 May 1940. Some casemates were destroyed. It remains unclear to what extent they slowed down the German advance. Several bridges fell undamaged into German hands.