The mobilization period in 1939–1940 did offer an opportunity to improve training standards, but those eight months were primarily spent on constructing defenses rather than on exercises, physical preparation, or mental readiness for a potential war. Additionally, the military failed to realistically simulate modern warfare during the few and inadequate training exercises that did take place.

Poorly Equipped

Another issue was that neutrality in the pre-war period forced military leadership to avoid publicly acknowledging the German threat, which led many soldiers to deny the danger entirely. Thus, when the German army crossed the Dutch border on May 10, 1940, the shock was immense. Dutch soldiers found themselves fighting in a war for which their army was woefully unprepared. Nevertheless, the soldiers at the Grebbeberg would offer more resistance to the German forces than their intelligence services had anticipated.

Der Teufelsberg (The Devil’s Mountain)

The Germans had planned to reach Rhenen from the German border via the Grebbeberg in one day. In reality, it took them four days. This significant delay was a remarkable achievement by the Dutch field army. The Germans spoke of the Berg with awe, and after the battle, the occupying forces gave it the nickname "Der Teufelsberg" (The Devil’s Mountain)—a covert tribute to the Dutch soldiers who defended the Grebbeberg against an overwhelming enemy.

Fighting at the Stop Line

Here, between Heimersteinselaan and the N225 provincial road, two sections—70 to 80 soldiers (from 2-III-8 R.I.)—were stationed under the command of Lieutenant Van den Boom on May 13. He wrote vividly about the battles at the stop line, battles for which the Dutch soldiers were so poorly prepared. A quote from his account:

"I also receive cries for help from the 1st section through Sergeant Landman and Sergeant Spijker. I send them back. Then Ensign van der Stam (from the 2nd section) arrives with the message that Sergeant Muetstege has been killed... but moments later, Muetstege himself appears. From his helmet down to his boots, he is covered in blood, and a set of teeth lies on his shoulder. A 3.7 cm shell had struck the machine gun nest of his group, taking the gunner’s head with it. Muetstege changes his clothes. Meanwhile, the helper has taken the machine gun and is preparing to fire from a position a few meters away behind the parapet. But before he can fire, his jaw is shattered. He still manages to reach the group’s first aid post on foot."

Retreat as the Only Option

The battle in this part of the stop line became increasingly hopeless. Ammunition supplies stagnated, artillery support could not be requested due to broken communications, and even their own mortars—located about 50 meters behind both sections—had fallen silent for various reasons. Continuing the fight was pointless; retreat was the only option. Lieutenant Van den Boom did not escape the German enemy during the withdrawal. He was captured and taken to Germany as a prisoner of war.