The immense importance attached to the work of the Engineers is strikingly illustrated by the fact that, whereas the army was increased to 19½ times its pre-war size, the enormous problems of field fortification, construction, and transportation, both with and behind the fighting forces, as well as the direction of many entirely new phases of warfare, necessitated an increase of the Corps of Engineers to 131½ times its strength at the beginning of the war. Prior to July, 1916, the corps consisted of only three battalions, with a total strength of not over 1,900 men, but when the Armistice was signed there had been organized, or were in process of organization, 500 Engineer units, with a strength of some 312,000 men, or more than 10 per cent of the entire army. Now it must be kept in mind that in the original corps of pre-war days the men were trained only as sappers and not in the countless specialist branches which were developed by the great conflict. The fundamental use of sapper troops is, theoretically, at least, the supervision of technical work during tactical operations. One regiment of sappers is normally assigned to each division, is under the immediate command of the divisional commander, and operates as directed by him. To this regiment is given the work of organizing positions for defense, which includes the construction of trenches, gun-positions, ammunition-dumps, and dugouts, the repair and maintenance of roads in the divisional area, the construction of shelters where required, and the general direction of the work necessary to keep open the lines of communication and supply. In open warfare it is customary for the divisional commander to hold his sapper regiment in reserve to be used for applying the decisive pressure or resistance at the moment when it is most needed. When going forward with the infantry, sapper troops usually have a definite technical mission, such as the organization of captured ground, the destruction of obstacles and the bridging of streams. During a retreat they are attached to the rear-guard, being charged with the demolition of bridges, the obstruction of roads, and the cutting of railway communications. Though the ranks of the Engineers were filled, for the most part, with men who were experts and specialists in certain trades and professions, they were time after time thrown into the line as combat troops, fighting shoulder to shoulder with the infantry. On more than one occasion they showed that, destitute of combat training though many of them were, they could handle a rifle or a machine-gun as well as an axe or a spade. At Cambrai the 11th (railway) Engineers, caught in the German counter-push, offered a stubborn and heroic resistance against overwhelming numbers. At Amiens another railway regiment, the 11th Engineers, formed a part of the little force with which General Sandeman Carey blocked the gap in the British line and thereby prevented the Germans from breaking through