The French devoted most of the summer to preparations for the great attack. The British took over thirty additional miles of the line, and thus released a large number of troops for the venture. New units were formed, and the factories worked night and day to produce the immense quantity of ammunition which would be needed. Artillery of every size and pattern, from light mountain guns to monster howitzers, were gradually brought together, until nearly 3,000 guns faced the Germans. Had these guns been placed side by side they would have extended for more than fifteen miles. Every battery knew exactly the portion of front which it was to attack. About twenty captive balloons, fitted with telephones and wires, were provided for directing the fire of the guns. A network of light railways was built in order to bring up the vast supplies of ammunition, and from the railhead a highroad nine miles long and forty feet wide was constructed across the plain. Dug-outs for men, stores for ammunition, and underground first-aid stations were constructed; and, so that the infantry could reach their positions without being destroyed by German shell fire, no less than forty miles of reserve and communication trenches were made. In some places saps and tunnels had been run out towards the German lines, so that the men making the first assault could spring suddenly from the earth. The hospitals were emptied ready for the stream of wounded that would soon flow into them. Officers and men were diligently instructed; everything was foreseen and provided for; nothing was left to chance.