第65章

The fact that it is not possible to maintain cornmunication over a distance exceeding some 20 miles is a severe handicap to the progressive development of wireless telegraphy in this field. It is a totally inadequate radius when the operations of the present war are borne in mind. A round journey of 200, or even more miles is considered a mere jaunt; it is the long distance flight which counts, and which contributes to the value of an airman's observations. The general impression is that the fighting line or zone comprises merely two or three successive stretches of trenches and other defences, representing a belt five miles or so in width, but this is a fallacy. The fighting zone is at least 20 miles in width; that is to say, the occupied territory in which vital movements take place represents a distance of 20miles from the foremost line of trenches to the extreme rear, and then comes the secondary zone, which may be a further 10miles or more in depth. Consequently the airman must fly at least 30 miles in a bee-line to cover the transverse belt of the enemy's field of operations. Upon the German and Russian sides this zone is of far greater depth, ranging up to 50 miles or so in width. In these circumstances the difficulties of ethereal communication 'twixt air and earth may be realised under the present limitations of radius from which it is possible to transmit.

But there are reasons still more cogent to explain why wireless telegraphy has not been used upon a more extensive scale during the present campaign. Wireless communication is not secretive.

In other words, its messages may be picked up by friend and foe alike with equal facility. True, the messages are sent in code, which may be unintelligible to the enemy. In this event the opponent endeavours to render the communications undecipherable to one and all by what is known as "jambing." That is to say, he sends out an aimless string of signals for the purpose of confusing senders and receivers, and this is continued without cessation and at a rapid rate. The result is that messages become blurred and undecipherable.

But there is another danger attending the use of wireless upon the battlefield. The fact that the stations are of limited range is well known to the opposing forces, and they are equally well aware of the fact that aerial craft cannot communicate over long distances. For instance, A sends his airmen aloft and conversation begins between the clouds and the ground. Presently the receivers of B begin to record faint signals. They fluctuate in intensity, but within a few seconds B gathers that an aeroplane is aloft and communicating with its base. By the aid of the field telephone B gets into touch with his whole string of wireless stations and orders a keen look-out and a listening ear to ascertain whether they have heard the same signals. Some report that the signals are quite distinct and growing louder, while others declare that the signals are growing fainter and intermittent. In this manner B is able to deduce in which direction the aeroplane is flying. Thus if those to the east report that signals are growing stronger, while the stations on the west state that they are diminishing, it is obvious that the aeroplane is flying west to east, and vice versa when the west hears more plainly at the expense of the east. If, however, both should report that signals are growing stronger, then it is obvious that the aircraft is advancing directly towards them.

It was this ability to deduce direction from the sound of the signals which led to the location of the Zeppelin which came down at Lun6ville some months previous to the war, and which threatened to develop into a diplomatic incident of serious importance. The French wireless stations running south-east to north-west were vigilant, and the outer station on the north-west side picked up the Zeppelin's conversation. It maintained a discreet silence, but communicated by telephone to its colleagues behind.

Presently No. 2 station came within range, followed by Nos. 3, 4, 5, 6, and so on in turn. Thus the track of the Zeppelin was dogged silently through the air by its wireless conversation as easily and as positively as if its flight had been followed by the naked eye. The Zeppelin travellers were quite ignorant of this action upon the part of the French and were surprised when they were rounded-up to learn that they had been tracked so ruthlessly. Every message which the wireless of the Zeppelin had transmitted had been received and filed by the French.

Under these circumstances it is doubtful whether wireless telegraphy between aircraft and the forces beneath will be adopted extensively during the present campaign. Of course, should some radical improvement be perfected, whereby communication may be rendered absolutely secretive, while no intimation is conveyed to the enemy that ethereal conversation is in progress, then the whole situation will be changed, and there may be remarkable developments.