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are therefore reproduced in the receiver as short or long notes. Readable signals can be obtained with about half a microampere, a main battery of one dry cell being sufficient. The employment of such an extremely small continuous line current eliminates danger of overhearing, induction being reduced to a minimum.

In the rear areas, simplex, duplex, and wheatstone telegraphy are all used in the offices of the higher formations, which in the case of the armies may contain several hundred telegraph instruments and telephone subscribers. Magneto exchanges are the rule as far for- ward as brigade headquarters. At brigade headquarters buzzer exchanges are also installed and at battery and battalion head- quarters buzzer exchanges are the rule. Circuits are of galvanized iron or copper wire beyond the limits of frequent shelling. For- ward of this, main routes are of buried armoured cable (2-, 4-, or 7-pair brass-sheathed or iron-armoured usually) or light field cables which are standardized in several sizes in both single and twisted twin circuits. Enamelled wire, that is, wire roughly insulated by a coating of enamel, was used by forward troops during the war, but is now obsolescent.

Wireless Telegraphy and Telephony. In all formations down to infantry battalions continuous wave wireless is now practically the only means used. There are three standard sets. For use at, or in rear of, army headquarters, or for long distances in mobile cam- paigns, a set is provided with a maximum range of 400 miles. The set has two 7o-foot masts and is fitted to be carried either in a box car or a limbered wagon. (This is the equivalent of the former " heavy motor set.")

For distances up to 200 m. a smaller set is provided which has two 4p-ft. masts and can be carried as above or on pack animals. For divisional work, the old " Wilson " and " British Field spark " sets have been replaced by a portable set with a range of 12 miles. This has two 15-ft. masts*,is worked from accumulators or by a hand generator, and carried on pack animals or by bearers.

Finally, the loop sets already mentioned earlier are retained for work within the battalion and battery if required, though they are likely to be replaced soon by short range and short wave C.VV. sets of much greater efficiency. The power buzzer and 3-valve amplifier sets are also available for issue in case of position warfare.

Small portable wireless telephone sets for forward work have been devised, and similar sets were indeed used in the Air Force during the last months of the war. The sets are not yet standardized, but those in use have a range of some 2,000 to 3,000 yards.

Visual Telegraphy. The visual instruments include the helio- graph as used in pre-war days (see 13.223); the Lucas lamp; the shutter, and the flag. Of these, the heliograph has a range up to loo m. or more, but is only of really extended use in a country with a large proportion of sunlight.

The very efficient and portable Lucas lamp is a powerful electric lamp with an 8-candle-power bulb set in the back of a cylindrical lampholder with a powerful reflector at its back. An 8-cell battery of ever-ready cells provides a current at an E.M.F. of 12 volts. The lamp has a range in daylight of 2 m. with the naked eye and 3 to 4 m. with the telescope, and at night of 6 m. with the naked eye and twice that distance with the telescope.

The signalling shutter is also a development of the position-war- fare phase of the war. It consists of three flaps of American cloth which are black on one side and white on the other. At the back of the shutter are metal clips by which the device can be attached to an ordinary bayonet. The flaps are normally closed with the black side outermost, but by pulling on the operating cord they are pulled down and the white exposed. On releasing the cord the flaps spring back to their original position. When not in use the instrument can be rolled up and stowed in a canvas case.

Message-carrying Agencies. Of these the most important are (a) despatch riders, mounted orderlies, or runners; (6) carrier pigeons; (c) message-carrying rockets; (d) dogs; (e) aircraft.

(a) For use in rear of brigade headquarters the motor cyclist despatch rider is invaluable. A feature of the modern signal service is the organized D.R.L.S. which deals with all official correspondence too urgent for post and not sufficiently urgent for the telegraph. Within brigades, divisions, and in cavalry units and formations, mounted orderlies are often used for conveying messages and this is true of all formations in country impassable to motor cyclists. In the forward battle zone the runner is the last resource of the for- ward commander. His use should, however, be restricted to occa- sions when all other means of signalling have failed or are unreliable, for casualties amongst runners are many and men suitable for this duty are not too common.

(5) The pigeon has proved its value for position-warfare condi- tions during the war. The pigeon service is controlled from corps headquarters and messages from the trenches will usually reach the battalion via brigade or divisional headquarters. The employment of pigeons with tanks and artillery is an important branch of the pigeon service. New developments are their delivery to isolated or front-line posts by aeroplane and parachute, and the teaching of pigeons to fly by night. In the latter case the birds are kept in red light and are flown to a loft where the trap is illuminated by a pow- erful arc or acetylene light.

(c) Message-carrying rockets with a range of 2,300 yd. have been adopted as a standard means of signalling. Their course through

the air is outlined by a trail of smoke and their position at the end of their flight by a coloured flare automatically lighted at the moment of impact with the ground.

(d) The use of the messenger dog is likely to be confined to posi- tion warfare. These dogs have done good service on occasion, but are likely to find their vocation only in stationary warfare or during a very methodical deployment for battle.

(e) In certain phases of a battle the aeroplane is the only trust- worthy or even possible intermediary between troops and com- mand. Apart from wireless telegraphy, messages can be communi- cated to the aeroplane by visual signalling, or if of a simple conven- tional character, by means of the ground panels used for the notifi- cation of positions, while, from the aeroplane to the ground, the most secure method yet discovered is to drop a written message, provided with long streamers, on to selected " dropping grounds " contiguous to the headquarters concerned.

Notification Signals. Light and smoke signals are made use of as occasion directs and a plentiful supply will be held in store. These are used, under prearranged schemes, for such purposes as calling for barrage or protective fire; notifying positions of forward troops; answering one-way messages, etc. The manufacture of dis- tinctive flares, and light signals generally, has been carried to a very high degree of perfection.

Acoustic signals have not been generally successful with the exception of the Klaxon horn in aircraft. Special sirens and horns for calling attention to gas attacks and other general alarms have been much used, but an attempt made by the French to signal by means of tuned acoustic horns was not very successful. The noises of a modern battle are such as to handicap this method of convey- ing information very greatly.

(6) The French Signal Service. The French intercommunica- tion service at the outbreak of war differed from the British in being in two separate compartments a telephone system con- trolled by the engineers, and a runner and despatch rider service under entirely separate direction. In addition there existed a motor service with the maintenance of liaison between units as its chief duty. The absence of the telegraph in forward forma- tions threw much extra work on the remaining personnel, and caused a consequent increase in the proportion of despatch riders, runners, and orderlies. Construction personnel was in the main kept in the rear and sent forward only when actually required, according to exigencies.

The greatest reliance was placed upon the ringing telephone even in the forward area, and this statement is true even for 1918, although time and again the forward telephone system had been swept away in hopeless ruin by the bombardments which pre- ceded the great position battles. In the rear, the very complete telephone network with an excellent system of locality exchanges served all purposes very well, whether in the normal stationary warfare, in the pressure of traffic before or during an attack from a trench system, or in the hurry of an advance or retreat on a con- siderable scale. In the last-named case as the attacking armies very soon outran the major portion of their heavy artillery, these well-built lines stood well, and the French system of locality exchanges served the retreating divisions as well as it had served the corps and armies for which it had been originally built.

In the forward area the French signal service was faced with a somewhat different problem from that which confronted the Brit- ish. Serving a professional staff and a conscript army, far more accustomed to mass manoeuvres than the British armies, a relatively far greater proportion of attention could be paid to getting back information from the front than orders forward to the front. The absence of the telegraph had also taught the for- ward staffs to rely more upon the spoken word and to dispense to a great extent with those written explanations and confirma- tions of orders which were considered essential to the British staff procedure.

The British subordinate commander was often able to act upon his own initiative; his French equivalent was not only able but expected to do so to a much greater degree. The result was a far greater use of one-way working, and to this was perhaps due the fact that the power buzzer essentially a one-way instrument was first developed in the French army.

A further feature as regards signal policy and practice was a tendency to confine forward routes to front-to-rear routes only. All lateral h'aison was by liaison officers, despatch riders, or run- ners. When a British division was working next the French, the position always involved responsibility for two lateral routes