In 1934, the German Army High Command (Oberkommando des Heeres (OKH)) commissioned Krupp of Essen to design a gun to destroy the forts of the French Maginot Line that were nearing completion. The gun's shells had to punch through seven metres of reinforced concrete or one full metre of steel armour plate, from beyond the range of French artillery. Krupp engineer Erich Müller calculated that the task would require a weapon with a calibre of around 80 cm, firing a projectile weighing 7 tonnes from a barrel 30 metres long. The weapon would have a weight of over 1000 tonnes. The size and weight meant that to be at all movable it would need to be supported on twin sets of railway tracks. In common with smaller railway guns, the only barrel movement on the mount itself would be elevation, traverse being managed by moving the weapon along a curved section of railway line. Krupp prepared plans for calibres of 70 cm, 80 cm, 85 cm, and 1 m.