In Spain, the anti-tank defense of the Nationalists was organized by the Wehrmacht officers, and the anti-tank guns were incorporated into a system of obstacles that were constructed with the intent to stop an attack by tanks by slowing it down, separating them from supporting infantry (advancing on foot) with machine-gun and mortar fire, and forcing tanks to conduct deliberate head-on assaults with engineer support, or seek a less-defended area to attack. Minefields laid with purpose-designed mines were used for the first time, destroying tank tracks, and forcing combat engineers to clear them on foot. Delay meant that Nationalist field artillery could engage the lightly armored Soviet tanks. This meant a change in Republican operational and eventually strategic planning, and a more protracted combat operations, with more casualties at a greater cost.