If you look closely, you will notice illogically straight lines on the Balloërveld that continue with a kink. The connection between all these lines only becomes evident on an aerial photograph: they form a star around the city of Assen. The Royal Air Force had them neatly in sight, so the liberators knew exactly where the bulldozer tank had to move forward to clear another such obstacle. The trenches were meant to make the advance of tanks impossible, but this proved futile. 

In Drenthe alone, at least 10,000 people worked on building the defence line. Assen was one of spearheads in that line that began in Delfzijl and ended in Arnhem. From the Port Natal sanatorium in Assen and Yde penal camp, among others, teams with shovels and wheelbarrows were sent out daily to dig for the enemy.  

The Todt Organisation could use anyone. They took people from prisons and penal camps, they used POWs, as well as volunteers and plain coercion. The remaining male population of Texel was accordingly ordered to march off to Drenthe. 

The kilometres of tank ditches, trenches, machine gun emplacements and bunkers stretched from Meppel along the canal to Bovensmilde, and from there through the Witterveld and the Asserbos and on across the Balloërveld to the north. On Balloërveld, one of the footpaths follows such a tank trench.