 Plastic armour could be applied by pouring it into a cavity formed by the steel backing plate and a temporary wooden form.Production of the armour was by road construction firms and was carried out in a similar way to the production of road coverings, the organization of the armouring being carried out by naval officers in key ports.In August 1939, the British Admiralty had considered the possibility that merchant ships might be attacked by aircraft with machine guns and cannon.