THE WORLD WAR General.—The War of 1914-18 has often been termed an engineers' war, a true description in so far that the increase in the engineer arm was proportionately much greater than in any other; but in the wider sense—the substitution of mechanical for human energy—field engineering made strangely little advance. The variety of work undertaken by military engineers and the numbers of men employed were alike immense. In the British army, on the outbreak of war, the engineer arm amounted to 2% of the total forces; in 1918 it had increased to 12% or r 6 % if the trans portation branch is included; during the same period the total engineer strength rose from under 14,00o to nearly 330,000. Tactical features varied from trench warfare, recalling the ancient art of siege-craft, to the most rapid movement of mobile columns; climatic conditions from the Arctic cold of Russia to the tropical heat of East Africa; while the enormous concentrations of men and material required, from engineers on lines of communication and at bases, constructional work on a scale previously unknown in war. The undoubted success of the British engineers in meeting these heavy demands is a testimonial to the basic soundness of their all-round training and elastic organization.
The heavy drain on French man-power in the early stages of the struggle made increases in the technical arms a matter of con tinuous difficulty, while serious drawbacks were inseparable from the system of entrusting rearward services to unfit and over-age personnel.
Engineer development in the German army followed much the same lines as in the British. The German engineers were always struggling to overcome the handicap of short numbers and lack of mutual understanding with which they started the war. They had constant difficulty in finding men for new scientific activities, and were further hampered by having to provide personnel to man the trench-mortar detachments which they initiated and kept throughout the war.
In the allocation of troops to the American army, based on the lessons of experience, provision for technical services was made on a far more liberal scale than had been found possible by any other nation.
Expansion and Work of the Royal Engineers.—Engineer units with the original expeditionary force consisted of a field squadron with the cavalry, one signal and two field companies per infantry division, one bridging train per corps, miscellaneous head quarters' signal units, and three small works or fortress companies for the base. Very early a third field company was added to each division ; also an infantry pioneer battalion. Fortress companies were reorganized and re-named "army troops companies"; they undertook all general field engineering outside divisional zones and were raised on a scale of one per division with additions for lines of communication. By degrees various special units were formed both for the field armies and the bases, including electrical and mechanical, workshop, stores, land drainage, water supply, etc. Special tunnelling companies, composed of miners from the colliery districts, were raised early in 1915. By the end of 1916 there were, including men from the Dominions, 25,00o in the field. The greatest mining operation in military history was carried out in connection with the capture of the Messines ridge in June 1917, when charges containing nearly a million pounds of explosive were fired under the German lines. Water supply necessitated work of great importance and variety. Before the battle of the Somme Ito power pumps and I tom. of 4in. pipe-line were installed, and were then added to as the battle progressed. In Flanders special purification processes were largely used; from one pump ing station alone 200,000 gallons of very impure Yser water were daily delivered, filtered and purified, to the troops. Special boring sections were formed for the chalk country, and deep well bores varying from 2ooft. to 7ooft. were sunk on the advice of geolo gists. For the Palestine campaign a pipe-line was laid across the desert, and filtered Nile water was delivered to a distance of over 150m. during the operations which drove the Turkish army from Beersheba. During the final three months of the war in France 326 steel girder bridges were erected by British and Dominion engineers, in addition to large numbers of timber and of pontoon equipment. Stock girders had been specially designed and details of erection carefully worked out during the long period of im mobility; a number of spans were capable of carrying weights up to 3o tons, a striking increase over the pre-war normal load of two tons.
Miscellaneous duties of the engineers included camouflage, anti-aircraft searchlights, survey (including flash-spotting and sound-ranging), chemical warfare, meteorology, geology, post office. Tanks, although organized as a separate arm, were com manded, from their first introduction in 1916 to the end of the war, by a Royal Engineer officer. The part played by officers of Royal Engineers in their conception and introduction is dis cussed under TANKS. A separate transportation branch was formed at the end of 1916 which assumed entire control of rail ways, normal and light, roads, inland water transport, cross channel ferry, port construction, dock working, ropeways, and all the stores, workshops and administrative services concerned. Sig nal units remained part of the corps of Royal Engineers through out the war, but formed practically an independent service. Faced with a multitude of new problems they underwent continual changes and expansion. During the first year of war 20,00om. of field cable were laid; and, during the final year, the amount was 245,000m., these figures being for France. The director of works at the base was responsible for engineering activities on a very great scale. Starting with but two assistants he controlled at the time of the Armistice a staff of nearly 200, in spite of having handed over forestry and engineer stores to independent directorates, and quarries to the transportation branch. Engineer stores were remarkable both for number and variety. A small proportion was procured in theatres of war by local purchase or production, but the main supplies were arranged for by the direc tor of fortifications and works at the War Office. Varying from sandbags to complete irrigation plant for Mesopotamia the monthly shipping tonnage several times exceeded 200,000 tons. Of sandbags 313 million were despatched in one year, and 4o million in one month alone to France.