Because of the complexity of the missile and the need for extensive testing prior to launch, the V-2's designers at the Peenemünde Army Research Center favoured using heavily defended fixed sites where the missiles could be stored, armed, and fuelled from an on-site LOX production plant before launching. But the German Army and the V-2 project's head, Major-General Walter Dornberger, were concerned that the sites would be vulnerable to aerial attack by the Allies. The Army's preferred option was to use "Meillerwagens", mobile firing batteries, which presented a much smaller target for the Allied air forces.