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494 the battle of Verdun in April 1916. A further development, made necessary by the adoption of elastic defence tactics in lieu of holding denned trench lines, was the so-called " shellhole " set, which comprised aerial, receiver, transmitter and source of power in a unit weighing only 40 pounds. In elastic defence the visual apparatus also played a useful part.

In trench warfare proper, the Germans did not employ buried cable to the same extent as the British. Their remedy for constant cutting of lines was to put the cables in open trenches sufficiently deep to save them from traffic, and to devote the greater part of the available labour to providing thorough protection for offices, and especially for repair squads. Cable-throwing mortars and messen- ger dogs carrying reels of self-unwinding cable were occasionally employed to lay lines in conditions of special difficulty. An apparatus known as the " Utel," analogous to the British fullerphone, was evolved to meet the overhearing danger. The visual Blinkgerdt, message-carrying projectiles and rockets, and especially pigeons, were used to supplement the telephone and the wireless communica- tions, as in the armies of the Entente. Unexpectedly good results were obtained with messenger dogs, powerful and intelligent wolflike animals,' specially trained and carefully bred.

For the great offensive battle of March 21 1918, the experiences both of the eastern and the western fronts were drawn upon. Between army and corps headquarters, and also between corps and division, the principle of the central route with a Meldekopf, to which all forward units made their connexion, was adopted. For the forward units special arrangements were made for transport and routes over the shellhole area. The wireless units were reorganized to permit of great subdivision, and the divisional wireless troop was equipped with its own transport. Visual apparatus was similarly made mobile and self-supporting, and a system of light, smoke, and other recognition signals completed the preparation for battle. In spite of losses and friction telephonic communication was suc- cessfully kept up as far forward as regimental headquarters during the first days of the offensive. Thereafter, however, the telephone system broke down owing to the inability of the sections to main- tain their lines against the enemy's shell fire and even more the ceaseless movement of transport in the ever-deepening battle zone. Pigeons, even, could finally only be got to the front units by means of aeroplanes. Earth telegraphy failed for want of range; message- carrying projectiles and dogs for the same reason were only occa- sionally useful, and in the later rapid stages of the advance inter- communication from front to rear depended almost entirely upon wireless telegraphy and upon simple notification signals (such as panels shown to aircraft, light and smoke signals of agreed mean- ing) in the hands of the troops themselves. The wireless system was based on the divisional central route, which was maintained by two powerful units, each alternately keeping up communication between Meldekopf and headquarters and moving forward to a new, more advanced Meldekopf. The small wireless sets distributed in the front zone, the other reporting agencies, and the staffs, made their connexion with the head of this extending route wherever it hap- pened to be at any moment, while the telephone units, largely rein- forced by fresh units hitherto reserved at the disposal of the supreme command and aided by captured material, followed on with airline. This system served its purpose, and the efforts of the signal service were rewarded by special mention in the communique of March 26, but normal signal traffic did not become possible again till the advance had slowed dc^vn sufficiently to enable the telephone units to catch it up.

In their rearward signal communications, the Germans made much use of Pupin coils to bring their iron wire (adopted from motives of economy) up to the technical efficiency of copper wire, and also to increase the efficiency of the jatter for long distance telephony. Direct telephonic communication between the German and the Turkish supreme commands was opened in 1917. The use of quick- writing telegraph instruments has already been alluded to. (C. F. A.)

(8) United States Army. In the United States army, the signal corps has been a separate organization for many years. The units into which it was organized in 1917-8, apart from those serving in the " S.O.S." or lines of communication in France, were of two main classes, field signal battalions and telegraph battalions. To an army were assigned two telegraph battalions and one field signal battalion; to each corps were assigned one telegraph battalion and one field signal battalion; and to each division, one field signal battalion. The telegraph battalions consisted of two companies each, while the field signal battalions each consisted of three companies, a wire company, a radio company, and an outpost company, the latter battalions including 470 men. The outpost company was responsible for communication at and in advance of infantry brigade headquarters working in four regimental sections in position warfare and in two brigade sections in mobile warfare. The radio company was equipped for all types of radio communication within the divisional area. The wire company constructed and operated the normal system of communications between the division head- quarters and the artillery headquarters between the former and infantry regimental headquarters. The corps and army signal units were responsible for maintaining and operating lines forward to the next subordinate headquarters and to certain troops of their own respective headquarters.

A distinct feature of the work of the United States army signal corps was the tendency for the preponderate use of the telephone over the telegraph and the very full and wide provision of telephone facilities. This characteristic is due to the fact that in the United States, the telephone organization is highly developed and the "telephone habit" wide-spread amongst all classes. Hence there would be a wider demand for such facilities, a greater familiarity in operating under circumstances of heavy traffic, and a greater manufacturing capacity for producing telephone equipment, than in the case of other countries.

The signal corps also included the meteorological, the pigeon and the radio direction-finding service and, until late in the war, the aviation service of the United States army.

SILESIA, UPPER.—It was provided in 1919 by the Peace of Versailles (Art. 88) that the inhabitants of Upper Silesia (pop. in 1919, 2,280,902) should be called upon to decide by a plebiscite whether they would belong to Germany or Poland (see 1922 Encyclopædia Britannica/Peace Conference). It should be noted that for the purpose of the plebiscite the purely German districts of Falkenberg (pop. 37,526), Grotthau (pop. 40,610), Neisse (pop. 7,781), part of Neustadt (pop. 25,000) and Hultschin (pop. 45,552), situated in the northern and western parts of Upper Silesia and representing a total population of about 156,469, were excluded. Up to the day of the plebiscite the supreme authority in the plebiscitary area was to be vested in an Inter-Allied Commission, consisting of one representative of France, Great Britain and Italy respectively. In this commission France was represented by Gen. Lerond, England by Col. Percival, and Italy by Gen. de Marini. On Feb. 1 1920 Allied troops occupied the plebiscitary district. The local German officials were then subordinated to the Inter-Allied authorities. The German police (Sicherheitspolizei) was replaced by a special polling police (Abstimmungspolizei), which was composed half of German-speaking, half of Polish-speaking, Upper Silesians.

On the whole the collaboration of the Inter-Allied control and the German officials proved satisfactory; but various differences arose, such as that which led to a strike of judges in May 1920. Both the Poles (under Korfanty) and the Germans opened an active canvassing campaign; and under Polish pressure the Germans in the southern and eastern districts were subjected to oppressive treatment. On Aug. 19 1920 the Poles felt strong enough, indeed, to make an attempt to seize the country by force. On all sides bands of Poles, chiefly recruited from Congress Poland, usurped authority. A number of Germans were forcibly carried across the frontier into Poland, and many were killed. Several weeks elapsed before it was possible to quell this rising and restore order. In the autumn of 1920 there was an exchange of notes between Germany and the Entente relating to the manner in which the plebiscite should be taken. It had been suggested by the Entente that the non-resident Upper Silesians of the German Reich should vote outside Upper Silesia, at Cologne. Germany protested against this, and her protest was recognized as valid by the Entente. In Jan. 1921 the date of the plebiscite was fixed for March 20 1921. An immediate revival took place in the use of terrorism by the Poles, especially in the districts of Rybnik, Pless, Kattowitz and Beuthen. It reached its climax in the days preceding the plebiscite. Voters from other parts of the German Reich were frequently refused admission to