第69章

Such mists as a rule comprise a relatively thin bank of low-lying vapour, which while enveloping the surface of the water in an impenetrable pall, yet permits the mast-heads of the vessels to stand out clearly, although they cannot be detected from the water-level or even from the control and fighting tops of a warship. A scouting waterplane, however, is able to observe them and note their movement, and accordingly can collect useful information concerning the apparent composition of the hidden force, the course it is following, its travelling speed, and so forth, which it can convey immediately to its friends.

The aeroplane has established its value in another manner.

Coal-burning vessels when moving at any pronounced speed invariably throw off large quantities of smoke, which may be detected easily from above, even when the vessels themselves are completely hidden in the mist. It was this circumstance which revealed the presence of the British squadron in the affair of the Bight of Heligoland.

The German airman on patrol duty from the adjacent base on the island of Heligoland detected the presence of this smoke, above the low-lying bank of fog, although there were no other visible signs of any vessels. Fully cognisant of the fact that the German Fleet was at anchor in a safe place he naturally divined that the smoke proceeded from a hostile squadron, evidently bent upon a raid. He returned to his headquarters, conveyed the intelligence he had collected to his superior officers, upon receipt of which a German cruiser squadron was sent out and engaged the British vessels to its own discomfiture. But for the airman's vigilance and smartness there is no doubt that the British squadron would have accomplished a great coup.

This incident, however, served to reveal that the aerial scout is prone to suffer from over-keenness and to collect only a partial amount of information. Upon this occasion the German watchman detected the presence of the British torpedo-boat and light cruiser force. Had he continued his investigations and made a wider sweep he would have discovered the proximity of the British battle-cruiser squadron which routed the German force, the latter having acted on incomplete information.

While the low-lying sea-fog is the navigator's worst enemy, it is the airman's greatest friend and protection. It not only preserves him against visual discovery from below, but is an excellent insulator of sound, so that his whereabouts is not betrayed by the noise of his motor. It is of in calculable value in another way. When a fog prevails the sea is generally as smooth as the pro verbial mirror, enabling the waterplanes to be brought up under cover to a suitable point from which they may be dispatched. Upon their release by climbing to a height of a few hundred feet the airmen are able to reach a clear atmosphere, where by means of the compass it is possible to advance in approximately the desired direction, safe from discovery from below owing to the fog. If they are "spotted" they can dive into its friendly depths, complete their work, and make for the parent ship.

Low-lying sea-fogs are favourable to aerial raids provided the scout is able to catch sight of the upper parts of landmarks to enable him to be sure of the correctness of his line of flight-in cases where the distance is very short compass direction is sufficiently reliable-because the bank of vapour not only constitutes a perfect screen, but serves as a blanket to the motor exhaust, if not completely, at least sufficiently to mislead those below. Fogs, as every mariner will testify, play strange tricks with the transmission of sound. Hence, although those on the vessels below might detect a slight hum, it might possibly be so faint as to convey the impression that the aviator was miles away, when, as a matter of fact, he was directly overhead. This confusion arising from sound aberration is a useful protection in itself, as it tends to lure a naval force lying in or moving through the fog into a false sense of security.

The development of the submarine revealed the incontrovertible fact that this arm would play a prominent part in future operations upon the water: a presage which has been adequately fulfilled during the present conflict. The instinct of self-preservation at once provoked a discussion of the most effective ways and means of disguising its whereabouts when it travels submerged. To this end the German naval authorities conducted a series of elaborate and interesting experiments off the island of Heligoland. As is well known, when one is directly above a stretch of shallow water, the bottom of the latter can be seen quite distinctly. Consequentiy, it was decided to employ aerial craft as detectives. Both the aeroplane and the dirigible took part in these experiments, being flown at varying heights, while the submarine was maneouvred at different depths immediately below. The sum of these investigations proved conclusively that a submarine may be detected from aloft when moving at a depth of from 30 to 40 feet. The outline of the submerged craft is certainly somewhat blurred, but nevertheless it is sufficiently distinct to enable its identity to be determined really against the background or bottom of the sea. To combat this detection from an aerial position it will be necessary inter alia to evolve a more harmonious or protective colour-scheme for the submarine.

Their investigations were responsible for the inauguration of the elaborate German aerial patrol of harbours, the base for such aerial operations being established upon the island of Heligoland.

So far the stern test of war as applied to the science of aeronautics has emphasised the fact that as a naval unit the dirigible is a complete failure. Whether experience will bring about a modification of these views time alone will show, but it is certain that existing principles of design will have to undergo a radical revision to achieve any notable results. The aeroplane alone has proved successful in this domain, and it is upon this type of aerial craft that dependence will have to be placed.