Tank spaced armour has been fielded since the First World War, when it was fitted to the French Schneider CA1 and Saint-Chamond tanks. The late variants of Panzer III had frontal spaced armour. A 20 mm thick face-hardened steel layer were in front of the 50 mm thick main armor. Impacted projectiles were physically damaged by the plate, so the main armor could withstand much greater hits. Due to lack of materials, German industry eventually switched to Rolled homogeneous armour (RHA), which is less effective and due to the slower production process, the technique was not widespread on German tanks.