In the case of seaplanes which might be carried on the deck of a battleship to a point reasonably contiguous to the object to be attacked, this difficulty was not so serious. This was demonstrated to some extent by the British raids on the German naval bases of Cuxhaven and Wilhelmshaven, but even in these instances it was bombs dropped by aviators, not gunfire that injured the enemy's works. But for the airplane proper this added weight was so positive a handicap as to practically destroy its usefulness as an a.s.sailant of fortified positions.

The heavier weapons of offence which could be carried by the airplane even of the highest development were the bombs. These once landed might cause the greatest destruction, but the difficulty of depositing them directly upon a desired target was not to be overcome. The dirigible balloon enjoyed a great advantage over the airplane in this respect, for it was able to hover over the spot which it desired to hit and to discharge its bombs in a direct perpendicular line with enough initial velocity from a spring gun to overcome largely any tendency to deviate from the perpendicular. But an airplane cannot stop. When it stops it must descend. If it is moving at the moderate speed of sixty miles an hour when it drops its missile, the bomb itself will move forward at the rate of sixty miles an hour until gravity has overcome the initial forward force.

Years before the war broke out, tests were held in Germany and France of the ability of aviators to drop a missile upon a target marked out upon the ground. One such test in France required the dropping of bombs from a height of 2400 feet upon a target 170 feet long by 40 broad--or about the dimensions of a small and rather stubby ship. The results were uniformly disappointing. The most creditable record was made by an American aviator, Lieutenant Scott, formerly of the United States Army. His first three shots missed altogether, but thereafter he landed eight within the limits. In Germany the same year the test was to drop bombs upon two targets, one resembling a captive Zeppelin, the other a military camp 330 feet square. The alt.i.tude limit was set at 660 feet. This, though a comparatively easy test, was virtually a failure. Only two compet.i.tors succeeded in dropping a bomb into the square at all, while the balloon was. .h.i.t but once.

The character and size of the bombs employed by aircraft naturally differed very widely, particularly as to size, between those carried by dirigibles and those used by airplanes. The Zeppelin sh.e.l.l varied in weight between two hundred and two hundred and fifty pounds. It was about forty-seven inches long by eight and a half inches in diameter. Its charge varied according to the use to which it was to be put. If it was hoped that it would drop in a crowded spot and inflict the greatest amount of damage to human life and limb it would carry a bursting charge, shrapnel, and bits of iron, all of which on the impact of the missile upon the earth would be hurled in every direction to a radius exceeding forty yards. If damage to buildings, on the other hand, was desired, some high explosive such as picric acid would be used which would totally wreck any moderate-sized building upon which the sh.e.l.l might fall. In many instances, particularly in raids upon cities such as London, incendiary sh.e.l.ls were used charged with some form of liquid fire, which rapidly spread the conflagration, and which itself was practically inextinguishable.

Sh.e.l.ls or bombs of these varying types were dropped from airplanes as well as from the larger and steadier Zeppelins. The difference was entirely in the size. It was said that a Zeppelin might drop a bomb of a ton's weight. But so far as attainable records are concerned it is impossible to cite any instance of this being done.

The effect on the great gas bag of the sudden release of a load so great would certainly cause a sudden upward flight which might be so quick and so powerful as to affect the very structure of the ship.

So far as known 250 pounds was the topmost limit of Zeppelin bombs, while most of them were of much smaller dimensions. The airplane bombs were seldom more than sixty pounds in weight, although in the larger British machines a record of ninety-five pounds has been attained. The most common form of bomb used in the heavier-than-air machines was pear-shaped, with a whirling tail to keep the missile upright as it falls. Steel b.a.l.l.s within, a little larger than ordinary shrapnel, are held in place by a device which releases them during the fall. On striking the ground they fall on the explosive charge within and the sh.e.l.l bursts, scattering the two or three hundred steel bullets which it carries over a wide radius. Bombs of this character weigh in the neighbourhood of six pounds and an ordinary airplane can carry a very considerable number. Their exploding device is very delicate so that it will operate upon impact with water, very soft earth, or even the covering of an airship. Other bombs commonly used in airplanes were shaped like darts, winged like an arrow so that they would fall perpendicularly and explode by a pusher at the point which was driven into the body of the bomb upon its impact with any hard substance.

It seems curious to read of the devices sometimes quite complicated and at all times the result of the greatest care and thought, used for dropping these bombs. In the trenches men pitched explosive missiles about with little more care than if they had been so many baseb.a.l.l.s, but only seldom was a bomb from aloft actually delivered by hand. In the case of the heavier bombs used by the dirigibles this is understandable. They could not be handled by a single man without the aid of mechanical devices. Some are dropped from a cradle which is tilted into a vertical position after the sh.e.l.l has been inserted. Others are fired from a tube not unlike the torpedo tube of a submarine, but which imparts only slight initial velocity to the missile. Its chief force is derived from gravity, and to be a.s.sured of its explosion the aviator must discharge it from a height proportionate to its size.

In the airplane the aviator's methods are more simple. Sometimes the bombs are carried in a rack beneath the body of the machine, and released by means of a lever at the side. A more primitive method often in use is merely to attach the bomb to a string and lower it to a point at which the aviator is certain that in falling it will not touch any part of the craft, and then cut the string. Half a dozen devices by which the aviator can hold the bomb at arm's length and drop it with the certainty of a perpendicular fall are in use in the different air navies. It will be evident to the most casual consideration that with any one of these devices employed by an aviator in a machine going at a speed of sixty miles an hour or more the matter of hitting the target is one in which luck has a very great share.

There is good reason for the pains taken by the aviators to see that their bombs fall swift and true, and clear of all the outlying parts of their machines. The grenadier in the trenches has a clear field for his explosive missile and he may toss it about with what appears to be desperate carelessness--though instances have been known in which a bomb thrower, throwing back his arm preparatory to launching his canned volcano, has struck the back of his own trench with disastrous results. But the aviator must be even more careful. His bombs must not hit any of the wires below his machine in falling--else there will be a dire fall for him. And above all they must not get entangled in stays or braces. In such case landing will bring a most unpleasant surprise.

A striking case was that of a bomber who had been out over the German trenches. He had a two-man machine, had made a successful flight and had dropped, effectively as he supposed, all his bombs.

Returning in serene consciousness of a day's duty well done, he was about to spiral down to the landing place when his pa.s.senger looked over the side of the car to see if everything was in good order.

Emphatically it was not. To his horror he discovered that two of the bombs had not fallen, but had caught in the running gear of his machine. To attempt a landing with the bombs in this position would have been suicidal. The bombs would have instantly exploded, and annihilated both machine and aviators. But to get out of the car, climb down on the wires, and try to unhook the bombs seemed more desperate still. Stabilizers, and other devices, now in common use, had not then been invented and to go out on the wing of a biplane, or to disturb its delicate balance, was unheard of. Nevertheless it was a moment for desperate remedies. The pilot clung to his controls, and sought to meet the shifting strains, while the pa.s.senger climbed out on the wing and then upon the running gear. To trust yourself two thousand feet in mid-air with your feet on one piano wire, and one hand clutching another, while with the other hand you grope blindly for a bomb charged with high explosive, is an experience for which few men would yearn. But in this case it was successful. The bombs fell--n.o.body cared where--and the two imperilled aviators came to ground safely.

A form of offensive weapon which for some reason seems peculiarly horrible to the human mind is the flechette. These are steel darts a little larger than a heavy lead pencil and with the upper two thirds of the stem deeply grooved so that the greater weight of the lower part will cause them to fall perpendicularly. These are used in attacks upon dense bodies of troops. Particularly have they proved effective in a.s.sailing cavalry, for the nature of the wounds they produce invariably maddens the horses who suffer from them and causes confusion that will often bring grave disaster to a transport or artillery train. Though very light, these arrows when dropped from any considerable height inflict most extraordinary wounds. They have been known to penetrate a soldier's steel helmet, to pa.s.s through his body and that of the horse he bestrode, and bury themselves in the earth. In the airplane they are carried in boxes of one hundred each, placed over an orifice in the floor. A touch of the aviator's foot and all are discharged. The speed of the machine causes them to fall at first in a somewhat confused fashion, with the result that before all have finally a.s.sumed their perpendicular position they have been scattered over a very considerable extent of air. Once fairly pointed downward they fall with unerring directness points downward to their mark.

[Ill.u.s.tration: _At a United States Training Camp._ U. & U.]

It is a curious fact that not long after these arrows first made their appearance in the French machines, they were imitated by the Germans, but the German darts had stamped upon them the words: "Made in Germany, but invented by the French."

[Ill.u.s.tration: _A "Blimp" with Gun Mounted on Top._ U. & U.]

One of the duties of the fighting airmen is to destroy the observation balloons which float in great numbers over both the lines tugging lazily at the ropes by which they are held captive while the observers perched in their baskets communicate the results of their observations by telephone to staff officers at a considerable distance. These balloons are usually anch.o.r.ed far enough back of their own lines to be safe from the ordinary artillery fire of their enemies. They were therefore fair game for the mosquitoes of the air. But they were not readily destroyed by such artillery as could be mounted on an ordinary airplane. Bullets from the machine-guns were too small to make any rents in the envelope that would affect its stability. Even if incendiary they could not carry a sufficiently heavy charge to affect so large a body. The skin of the "sausages," as the balloons were commonly called from their shape, was too soft to offer sufficient resistance to explode a sh.e.l.l of any size. The war was pretty well under way before the precise weapon needed for their destruction was discovered. This proved to be a large rocket of which eight were carried on an airplane, four on each side. They were discharged by powerful springs and a mechanism started which ignited them as soon as they had left the airplane behind. The head of each rocket was of pointed steel, very sharp and heavy enough to pierce the balloon skin. Winslow was fortunate enough to be present when the first test of this weapon was made. In his book, _With the French Flying Corps_, he thus tells the story:

Swinging lazily above the field was a captive balloon. At one end of Le Bourget was a line of waiting airplanes. "This is the second; they have already brought down one balloon," remarked the man at my elbow. The hum of a motor caused me to look up. A wide-winged double motor, Caudron, had left the ground and was mounting gracefully above us. Up and up it went, describing a great circle, until it faced the balloon. Everyone caught his breath. The Caudron was rushing straight at the balloon, diving for the attack.

"Now!" cried the crowd. There was a loud crack, a flash, and eight long rockets darted forth leaving behind a fiery trail. The aviator's aim however was wide, and to the disappointment of everyone the darts fell harmlessly to the ground.

Another motor roared far down the field, and a tiny _appareil de cha.s.se_ shot upward like a swallow. "A Nieuport," shouted the crowd as one voice. Eager to atone for his _copain's_ failure, and impatient at his delay in getting out of the way, the tiny biplane tossed and tumbled about in the air like a clown in the circus ring.

"Look! he's looping! he falls! he slips! no, he rights again!"

cried a hundred voices as the skilful pilot kept our nerves on edge.

Suddenly he darted into position and for a second hovered uncertain. Then with a dive like that of a dragon-fly, he rushed down to the attack. Again a sheet of flame and a shower of sparks. This time the balloon sagged. The flames crept slowly around its silken envelope. "_Touchez!_" cried the mult.i.tude.

Then the balloon burst and fell to the ground a ma.s.s of flames.

High above the little Nieuport saucily continued its pranks, as though contemptuous of such easy prey.

[Ill.u.s.tration: _Aviators Descending in Parachutes from a Balloon Struck by Incendiary Sh.e.l.ls._ U. & U.]

It may be properly noted at this point that the captive balloons or kite balloons have proved of the greatest value for observations in this war. Lacking of course the mobility of the swiftly moving airplanes, they have the advantage over the latter of being at all times in direct communication by telephone with the ground and being able to carry quite heavy scientific instruments for the more accurate mapping out of such territory as comes within their sphere of observation. They are not easy to destroy by artillery fire, for the continual swaying of the balloon before the wind perplexes gunners in their aim. At a height of six hundred feet, a normal observation post, the horizon is nearly thirty miles from the observer. In flat countries like Flanders, or at sea where the balloon may be sent up from the deck of a ship, this gives an outlook of the greatest advantage to the army or fleet relying upon the balloon for its observations of the enemy's dispositions.

[Ill.u.s.tration: _The Balloon from which the Aviators Fled._ U. & U.]

Most of the British and French observation balloons have been of the old-fashioned spherical form which officers in those services find sufficiently effective. The Germans, however, claimed that a balloon might be devised which would not be so very unstable in gusty weather. Out of this belief grew the Pa.r.s.eval-Siegfeld balloon which from its form took the name of the Sausage. In fact its appearance far from being terrifying suggests not only that particular edible, but a large dill pickle floating awkwardly in the air. In order to keep the balloon always pointed into the teeth of the wind there is attached to one end of it a large surrounding bag hanging from the lower half of the main envelope. One end of this, the end facing forward, is left open and into this the wind blows, steadying the whole structure after the fashion of the tail of a kite. The effect is somewhat grotesque as anyone who has studied the numerous pictures of balloons of this type employed during the war must have observed. It looks not unlike some form of tumor growing from a healthy structure.

Captive or kite balloons are especially effective as coast guards.

Posted fifty miles apart along a threatened coast they can keep a steady watch over the sea for more than twenty-five miles toward the horizon. With their telephonic connections they can notify airplanes in waiting, or for that matter swift destroyers, of any suspicious sight in the distance, and secure an immediate investigation which will perhaps result in the defeat of some attempted raid. Requiring little power for raising and lowering them and few men for their operation, they form a method of standing sentry guard at a nation's front door which can probably be equalled by no other device. The United States at the moment of the preparation of this book is virtually without any balloons of this type--the first one of any pretensions having been tested in the summer of 1917.

As late as the third year of the war it could not be said that the possibilities of aerial offense had been thoroughly developed by any nation. The Germans indeed had done more than any of the belligerents in this direction with their raids on the British coast and on London. But, as already pointed out, these raids as serious attacks on strategic positions were mere failures. Advocates of the increased employment of aircraft in this fashion insist that the military value to Germany of the raids lay not so much in the possibility of doing damage of military importance but rather in the fact that the possibility of repeated and more effective raids compelled Great Britain to keep at home a force of thirty thousand to fifty thousand men constantly on guard, who but for this menace would have been employed on the battlefields of France. In this argument there is a measure of plausibility. Indeed between January, 1915, and June 13, 1917, the Germans made twenty-three disastrous raids upon England, killing more than seven hundred persons and injuring nearly twice as many. The amount of damage to property has never been reported nor is it possible to estimate the extent of injury inflicted upon works of a military character. The extreme secrecy with which Great Britain, in common with the other belligerents, has enveloped operations of this character makes it impossible at this early day to estimate the military value of these exploits. Merely to inflict anguish and death upon a great number of civilians, and those largely women and children, is obviously of no military service. But if such suffering is inflicted in the course of an attack which promises the destruction or even the crippling of works of military character like a.r.s.enals, munition plants, or naval stores, it must be accepted as an incident of legitimate warfare.

The limited information obtainable in wartime seems to indicate that the German raids had no legitimate objective in view but were undertaken for the mere purpose of frightfulness.

The methods of defence employed in Great Britain, where all attacks must come from the sea, were mainly naval. What might be called the outer, or flying, defences consisted of fast armed fighting seaplanes and dirigibles. Stationed on the coast and ready on the receipt of a wireless warning from scouts, either aerial or naval, that an enemy air flotilla was approaching the coast, they could at once fly forth and give it battle. A thorough defence of the British territory demanded that the enemy should be driven back before reaching the land. Once over British territory the projectiles discharged whether by friend or foe did equal harm to the people on the ground below. Accordingly every endeavour was made to meet and beat the raiders before they had pa.s.sed the barrier of sea. Beside the flying defences there were the floating defences. Anti-aircraft guns were mounted on different types of ships stationed far out from the sh.o.r.e and ever on the watch. But these latter were of comparatively little avail, for flying over the Channel or the North Sea the invaders naturally flew at a great height. They had no targets there to seek, steered by their compa.s.ses, and were entirely indifferent to the prospect beneath them. Moreover anti-aircraft guns, hard to train effectively from an immovable mount, were particularly untrustworthy when fired from the deck of a rolling and tossing ship in the turbulent Channel.

Third in the list of defences of the British coast, or of any other coast which may at any time be threatened with an aerial raid, are defensive stations equipped not only with anti-aircraft guns and searchlights but with batteries of strange new scientific instruments like the "listening towers," equipped with huge microphones to magnify the sound of the motors of approaching aircraft so that they would be heard long before they could be seen, range finders, and other devices for the purpose of gauging the distance and fixing the direction of an approaching enemy.

Some brief attention may here be given to the various types of anti-aircraft guns. These differ very materially in type and weight in the different belligerent armies and navies. They have but one quality in common, namely that they are most disappointing in the results attained. Mr. F. W. Lancaster, the foremost British authority on aircraft, says on this subject:

"Anti-aircraft firing is very inaccurate, hence numbers of guns are employed to compensate."

[Ill.u.s.tration: Photo by International Film Service.

_German Air Raiders over England._

_In the foreground three British planes are advancing to the attack._]

That is to say that one or two guns can be little relied upon to put a flyer _hors du combat_. The method adopted is to have large batteries which fairly fill that portion of the air through which the adventurous airman is making his way with sh.e.l.ls fired rather at the section than at the swiftly moving target.

"Archibald," the British airmen call, for some mysterious reason, the anti-aircraft guns employed by their enemies, sometimes referring to a big howitzer which made its appearance late in the war as "Cuthbert."

The names sound a little effeminate, redolent somehow of high teas and the dancing floor, rather than the field of battle. Perhaps this was why the British soldiers adopted them as an expression of contempt for the enemy's batteries. But contempt was hardly justifiable in face of the difficulty of the problem. A gun firing a twenty-pound shrapnel sh.e.l.l is not pointed on an object with the celerity with which a practised revolver shot can throw his weapon into position. The gunner on the ground seeing an airplane flying five thousand feet above him--almost a mile up in the air--hurries to get his piece into position for a shot. But while he is aiming the flyer, if a high-speed machine, will be changing its position at a rate of perhaps 120 miles an hour. Nor does it fly straight ahead. The gunner cannot point his weapon some distance in advance as he would were he a sportsman intent on cutting off a flight of wild geese. The aviator makes quick turns--zigzags--employs every artifice to defeat the aim of his enemy below. Small wonder that in the majority of cases they have been successful. The att.i.tude of the airmen toward the "Archies" is one of calm contempt.

The German mind being distinctly scientific invented early in the war a method of fixing the range and position of an enemy airplane which would be most effective if the target were not continually in erratic motion. The method was to arrange anti-aircraft guns in a triangle, all in telephonic connection with a central observer. When a flyer enters the territory which these guns are guarding, the gunner at one of the apexes of the triangle fires a sh.e.l.l which gives out a red cloud of smoke. Perhaps it falls short. The central observer notes the result and orders a second gun to fire. Instantly a gunner at another apex fires again, this time a sh.e.l.l giving forth black smoke. This sh.e.l.l discharged with the warning given by the earlier one is likely to come nearer the target, but at any rate marks another point at which it has been missed. Between the two a third gunner instantly corrects his aim by the results of the first two shots. His sh.e.l.l gives out a yellow smoke. The observer then figures from the positions of the three guns the lines of a triangular cone at the apex of which the target should be. Sometimes science wins, often enough for the Germans to cling to the system.

But more often the shrewd aviator defeats science by his swift and eccentric changes of his line of flight.

At the beginning of the war Germany was very much better equipped with anti-aircraft guns than any of her enemies. This was due to the remarkable foresight of the great munition makers, Krupp and Ehrhardt, who began experimenting with anti-aircraft guns before the aircraft themselves were much more than experiments. The problem was no easy one. The gun had to be light, mobile, and often mounted on an automobile so as to be swiftly transferred from place to place in pursuit of raiders. It was vital that it should be so mounted as to be speedily trained to any position vertical or horizontal. As a result the type determined upon was mounted on a pedestal fixed to the cha.s.sis of an automobile or to the deck of a ship in case it was to be used in naval warfare. The heaviest gun manufactured in Germany was of 4-1/4-inch calibre, throwing a sh.e.l.l of forty pounds weight. This could be mounted directly over the rear axle of a heavy motor truck. To protect the structure of the car from the shock of the recoil these guns are of course equipped with hydraulic or other appliances for taking it up. They are manufactured also in the 3-inch size. Germany, France, and England vied with each other in devising armored motor cars equipped with guns of this type--the British using the makes of Vickers and Hotchkiss, and the French their favourite Creusot. The trucks are always armoured, the guns mounted in turrets so that the effect is not unlike that of a small battleship dashing madly down a country road and firing repeatedly at some object directly overhead. But the record has not shown that the success of these picturesque and ponderous engines of war has been great. They cannot manoeuvre with enough swiftness to keep up with the gyrations of an airplane. They offer as good a target for a bomb from above as the aircraft does to their shots from below.

Indeed they so thoroughly demonstrated their inefficiency that before the war had pa.s.sed its third year they were either abandoned or their guns employed only when the car was stationary. Shots fired at full speed were seldom effective.

The real measure of the effectiveness of anti-aircraft guns may be judged by the comparative immunity that attended the aviators engaged on the two early British raids on Friedrichshaven, the seat of the great Zeppelin works on Lake Constance, and on the German naval base at Cuxhaven. The first was undertaken by three machines.

From Belfort in France, the aviators turned into Germany and flew for 120 miles across hostile territory. The flight was made by day though indeed the adventurous aviators were favoured by a slight mist. Small single seated "avro" machines were used, loaded heavily with bombs as well as with the large amount of fuel necessary for a flight which before its completion would extend over 250 miles. Not only at the frontier, but at many fortified positions over which they pa.s.sed, they must have exposed themselves to the fire of artillery, but until they actually reached the neighbourhood of the Zeppelin works they encountered no fire whatsoever. There the attack on them was savage and well maintained. On the roofs of the gigantic factory, on neighbouring hillocks and points of vantage there were anti-aircraft guns busily discharging shrapnel at the invaders. It is claimed by the British that fearing this attack the Germans had called from the front in Flanders their best marksmen, for at that time the comparative worthlessness of the Zeppelin had not been demonstrated and the protection of the works was regarded as a prime duty of the army.

[Ill.u.s.tration: U. & U.

_One Aviator's Narrow Escape._]

The invading machines flew low above the factory roofs. The adventurers had come far on an errand which they knew would awaken the utmost enthusiasm among their fellows at home and they were determined to so perform their task that no charge of having left anything undone could possibly lie. Commander Briggs, the first of the aviators to reach the scene, flew as low as one hundred feet above the roofs, dropping his bombs with deadly accuracy. But he paid for his temerity with the loss of his machine and his liberty.

A bullet pierced his petrol tank and there was nothing for him to do save to glide to earth and surrender. The two aviators who accompanied him although their machines were repeatedly hit were nevertheless able to drop all their bombs and to fly safely back to Belfort whence they had taken their departure some hours before. The measure of actual damage done in the raid has never been precisely known. Germany always denied that it was serious, while the British ascribe to it the greatest importance--a clash of opinion common in the war and which will for some years greatly perplex the student of its history.

The second raid, that upon Cuxhaven, was made by seaplanes so far as the air fighting was concerned, but in it not only destroyers but submarines also took part. It presented the unique phenomenon of a battle fought at once above, upon, and below the surface of the sea.

It is with the aerial feature of the battle alone that we have to do.

Christmas morning, 1915, seven seaplanes were quietly lowered to the surface of the water of the North Sea from their mother ships a little before daybreak. The spot was within a few miles of Cuxhaven and the mouth of the River Elbe. As the aircraft rose from the surface of the water and out of the light mist that lay upon it, they could see in the harbour which they threatened, a small group of German warships. Almost at the same moment their presence was detected. The alarms of the bugles rang out from the hitherto quiet craft and in a moment with the smoke pouring from their funnels destroyers and torpedo boats moved out to meet the attack. Two Zeppelins rose high in the air surrounded by a number of the smaller airplanes, eager for the conflict. The latter proceeded at once to the attack upon the raiding air fleet, while the destroyers, the heavier Zeppelins, and a number of submarines sped out to sea to attack the British ships. The mist, which grew thicker, turned the combat from a battle into a mere disorderly raid, but out of it the seaplanes emerged unhurt. All made their way safely back to the fleet, after having dropped their bombs with a degree of damage never precisely known. The weakness of the seaplane is that on returning to its parent ship it cannot usually alight upon her deck, even though a landing platform has been provided. It must, as a rule, drop to the surface of the ocean, and if this be at all rough the machine very speedily goes to pieces. This was the case with four of the seven seaplanes which took part in the raid on Cuxhaven.

All however delivered their pilots safely to the awaiting fleet and none fell a victim to the German anti-aircraft guns.

In May of 1917, the British Royal Naval Air Service undertook the mapping of the coast of Belgium north from Nieuport, the most northerly seaport held by the British, to the southern boundary of Holland. This section of coast was held by the Germans and in it were included the two submarine bases of Zeebrugge and Ostend. At the latter point the long line of German trenches extending to the boundary of Switzerland rested its right flank on the sea. The whole coast north of that was lined with German batteries, snugly concealed in the rolling sand dunes and masked by the waving gra.s.ses of a barren coast. From British ships thirty miles out at sea, for the waters there are shallow and large vessels can only at great peril approach the sh.o.r.e, the seaplanes were launched. Just south of Nieuport a land base was established as a rendezvous for both air-and seaplanes when their day's work was done. From fleet and station the aerial observers took their way daily to the enemy's coast. Every mile of it was photographed. The hidden batteries were detected and the inexorable record of their presence imprinted on the films. The work in progress at Ostend and Zeebrugge, the active construction of basins, locks, and quays, the progress of the great mole building at the latter port, the activities of submarines and destroyers within the harbour, the locations of guns and the positions of barracks were all indelibly set down. These films developed at leisure were made into coherent wholes, placed in projecting machines, and displayed like moving pictures in the ward rooms of the ships hovering off sh.o.r.e, so that the naval forces preparing for the a.s.sault had a very accurate idea of the nature of the defences they were about to encounter.