Fort Spijkerboor is one of the two modern forts of the Position Amsterdam to be equipped with a gun turret. Spijkerboor eventually got a turret for two 10,5 cm delivered by Krupp. The turret was quite advanced for those days, but it was too expensive to install it in other forts. That's why the turret remains unique.

The other forts only had light 5,7 cm retractable turrets for infantry defense. Other forts had to be equipped with heavier gun turrets, but they were considered to be too expensive, especially when looking at their strategic value. The army prefered guns in open position behind the line which were easier to camouflage and which could change position if necessary.