of the remaining months of mobile warfare is that of the reversion to simple skeleton systems, based on the principle of the central route studded at suitable intervals with forward communication centres. No further radical reorganization took effect, the princi- pal change being the gradual switching over from spark to continu- ous wave wireless for command intercommunication purposes.
(3) Signals in Theatres of War other than France. While the greatest measure of evolution and adaptation naturally took place in the most important field and that nearest to the home sources of supply, almost every one of the outlying British thea- tres of war presented its special problems and emphasized the need of forethought and careful preparations, in respect of methods, personnel and stores alike, to suit local conditions, for instance in arranging for intimate cooperation with the inter- communication service of the navy in such operations as those of the Dardanelles, and the coastal operations of Sinai and Syria, 1 and in assigning an unusually large part to visual and wireless communications when a considerable water gap has to be spanned, as in the Dardanelles campaign. But perhaps the most significant lesson of experience in these campaigns was the greatly enhanced importance of wireless telegraphy relatively to other means of communication. Wireless plays a predominant part in such operations as those in E., W. and S.W. Africa, or those of the desert mounted corps in Palestine, which are con- ducted in vast, ill-developed theatres of war by comparatively small forces; for these frequently involve far-flung troop move- ments in the offensive, and tactical isolation of detachments in the defensive.
The sets in use in the British Expeditionary Forces engaged in outlying theatres were the 3-K.W. lorry set; the iJ-K.W. set mounted on a limbered wagon and drawn by teams of horses, bul- locks, mules, or even men; and the Marconi pack set, a O-5-K.W. set either carried in a limbered wagon, on pack horses or mules, or by bearers. The latter proved particularly valuable for work with flying columns of swiftly moving troops. All three types of set were spark sets deriving their energy from internal-combustion engines. In the future, these will doubtless be replaced by the more efficient continuous wave system of wireless, but they played their part well in the 1914-8 campaigns over ranges respectively of 120- 100, 80, and 30-50 miles. The extreme case of isolation in the defensive is of course that of a garrison under prolonged siege, and as an example both of the utility of wireless telegraphy in this case and of the actual working output of even a small set, the case of Kut may be quoted. The only means of signalling possessed by the defenders of Kut for some weeks was a small wireless set. By means of this, touch was kept with the relieving forces until the surrender, 6,313 messages consisting of 434,861 words in 144 days being the final record of the set.
One other lesson learnt in the outlying campaigns may be men- tioned the special necessity, in the theatres far from home supply services, for standardization of implements and stores. This had only been partially carried out when the war ended, but since then a con- siderable reduction has been effected in the number of types of instruments in use.
(4) Relation to other Arms. A subject of considerable impor- tance is the relation between signals and other arms. Before the World War, the signal service was regarded by the general staff as an executive servant and by other elements of the army its existence and potentialities were too often slighted or ignored altogether. As the war went on, the importance of rapid, trust- worthy, and copious intercommunication was emphasized more and more. The effect of this, in the gradual change in the status of the formation signal officer from the executive to the staff officer, has already been emphasized as one of the main features of the evolution of the service during the war period. Similarly, the relation of " signals " to intelligence, artillery, and even to infantry, has undergone a distinct change.
The intelligence service of all armies owes no small measure of its present effectiveness to the means provided by signals for tapping sources of enemy information. The listening sets; the position-finding wireless set; the interception wireless set; the
1 It was doubtless owing largely to the experience of these cam- paigns that steps were taken towards the end of the war to har- monize the signal procedure of the navy, the army and the post- office, that is, the form and manner of sending messages, the checks in accuracy, the ensuring of priority, and suchlike matters of techni- cal detail that, in fact, are as important to efficiency as the design of instruments and the principles observed in their employment.
aeroplane wireless compass, are all efficient means of making out enemy plans and dispositions. So-called " wireless camouflage" 2 and the dissemination of false information by all means of signal- ling are well-recognized strategems.
The relation between artillery and the signal service is still more obvious. Efficient artillery fire was never more dependent on good observation than it was in the position-warfare battles of 1915-7, and observation is useless without intercommunica- tion. As has been noted earlier in this article, artillery signal communication has become one of the definite functions of the signal service.
With the infantry, the signal service, through the regimental signal personnel which it supervises, has an equally close con- nexion, though the personal comradeship which is the basis of true liaison was made difficult, in the war, by the inevitable demands made on infantry labour for the burying of cables.
Signal personnel have frequently proved their ability to give a good account of themselves in infantry fighting, but it cannot be too strongly emphasized that the employment of signallers as infan- trymen whether in the battalion, brigade, division, corps, or army, is a mistake except as a very last resource. The signaller is a valu- able technical tradesman and he cannot be trained in a few days or even a few months. More casualties have probably been caused by lack of signallers, and therefore of the efficient signal communica- tions essential to the guidance of the battle, than can ever have been saved by their employment in the fighting line.
No small amount of the attention of signal units, especially in position warfare, is now devoted to ^ferving the needs of other technical branches of the army. Tank corps, royal air force, and survey battalions all made special demands upon the intercom- munication service.
(5) Means of Intercommunication. Details of the means of intercommunication employed by the British army signal service will be found in the official Manual of the Corps of Signals, Parts I., III., IV., and V. Some of the details of more general interest are given in the following few paragraphs.
Telephone and Telegraph. The standard instruments in use are the telephone No. no (magneto ringing), the fullerphone (buzzer call) and the telephone D Mk. III. (buzzer call). (In addition, a lineman's telephone is provided for the use of the intercommunica- tion maintenance personnel which has both magneto ring and buz- zer call.) Of the telephones, no special description is needed, their only peculiar characteristic being a robustness of structure and parts calculated to stand the rough usage of army life.
Line Secondary C" Cs
FIG. 2.
The fullerphone is an instrument of peculiar interest. The chief cause of the leakage from telegraph and telephone circuits was the electrical stresses set up within the earth by the rapidly alternating current used. The fullerphone is a telegraph instrument, the essen- tial point of which is the changing at the receiving end of a steady current into an intermittent current of audible frequency, while at the same time the current in the line remains steady. A typical fullerphone receiving circuit is shown in fig. 2. The interrupter (X) may be driven by any means, either electrical or mechanical. In army patterns it is driven electrically, being operated by means of a local cell.
If a steady E.M.F. is applied between line and earth and the cir- cuit is closed at the interrupter, a steady current will pass through the choke coils (Cl, 2), contact 2 and receiver. If the circuit is broken at X the current cannot pass through the receiver but will flow into the condensers (Ki, K2, K3_). When the circuit is again closed at X the condensers partially discharge through the receiver.
When the interrupter is working we therefore get an intermittent current in the receiver which can be made audible by adjusting the interrupter to run at a suitable speed, while the line current alter- nately runs into the condensers or through the receivers and remains practically constant and continuous in the line. The dots and dashes sent by the single current Morse key at the end of the line
2 Manipulating the technicalities and the volume of traffic of one's own wireless so as to mislead the enemy's interception service.
