Chapter XI : ARMOURED AEROPLANES

The stern test of war has served to reveal conclusively the factthat aerial craft can be put out of action readily andeffectively, when once the marksman has picked up the range,whether the gunner be conducting his operations with an anti-aircraft gun stationed upon the ground, or from a hostilemachine. It will be remembered that Flight-Commander Briggs, onthe occasion of the daring British raid upon the Zeppelin shedsat Friedrichshafen, was brought to the ground by a bullet whichpenetrated his fuel tank. Several other vessels, British,German, French, and Russian alike, have been thrown out of actionin a similar manner, and invariably the craft which has beendisabled suddenly in this way has fallen precipitately to earthin the fatal headlong dive.

Previous to the outbreak of hostilities there was considerabledivergence of opinion upon this subject. The general opinion wasthat the outspread wings and the stays which constituted theweakest parts of the structure were most susceptible to gun-fire,and thus were likely to fail. But practice has proved that it isthe driving mechanism which is the most vulnerable part of theaeroplane.

This vulnerability of the essential feature of the flying machineis a decisive weakness, and exposes the aviator to a constantmenace. It may be quite true that less than one bullet in athousand may hit the machine, but when the lucky missile doesfind its billet its effect is complete. The fact must not beoverlooked that the gunners who work the batteries ofanti-aircraft guns are becommg more and more expert as a resultof practice, so that as time progresses and improved guns forsuch duty are rendered available, the work of the aviator islikely to become more dangerous and difficult. Experience hasproved that the high velocity gun of to-day is able to hurl itsprojectile or shell to an extreme height--far greater than waspreviously considered possible--so that considerable discretionhas to be exercised by the airman, who literally bears his lifein his hands.

Although elaborate trials were carried out upon the testingranges with the weapons devised especially for firing upon flyingmachines, captive balloons being employed as targets, the datathus obtained were neither conclusive nor illuminating. Theactual experiences of airmen have given us some very instructivefacts upon this point for the first time.

It was formerly held that the zone of fire that is to beconsidered as a serious danger was within a height of about 4,500feet. But this estimate was well within the mark. Airmen havefound that the modern projectiles devised for this phase ofoperations are able to inflict distinctly serious damage at analtitude of 9,000 feet. The shell itself may have but little ofits imparted velocity remaining at this altitude, but it must beremembered that when the missile bursts, the contents thereof aregiven an independent velocity, and a wide cone of dispersion,which is quite sufficient to achieve the desired end, inasmuch asthe mechanism of the modern aeroplane and dirigible is somewhatdelicate.

It was for this reason that the possibility of armouring theairship was discussed seriously, and many interesting experimentsin this field were carried out. At the same time it was decidedthat the armouring should be effected upon lines analogous tothat prevailing in warship engineering. The craft should notonly be provided with defensive but also with aggressivearmament. This decision was not viewed with general approbation. It was pointed out that questions of weight would arise,especially in relation to the speed of the machine. Increasedweight, unless it were accompanied by a proportionateaugmentation of power in the motor, would react against theefficiency and utility of the machine, would appreciably reduceits speed, and would affect its climbing powers very adversely.In some quarters it was maintained that as a result the machinewould even prove unsuited to military operations, inasmuch ashigh speed is the primary factor in these.

Consequently it was decided by the foremost aviating experts thatmachines would have to be classified and allotted to particularspheres of work, just as warships are built in accordance withthe special duty which they are expected to perform. Inreconnaissance, speed is imperative, because such work in the aircoincides with that of the torpedo-boat or scout upon the seas. It is designed to acquire information respecting the movements ofthe enemy, so as to assist the heavier arms in the plan ofcampaign. On the other hand, the fighting corsair of the skiesmight be likened to the cruiser or battleship. It need notpossess such a high turn of speed, but must be equipped withhard-hitting powers and be protected against attacking fire.

One attempt to secure the adequate protection against gun-firefrom the ground assumed the installation of bullet-proof steelplating, about one fifth of an inch thick, below the tank and themotor respectively. The disposition of the plating was such asto offer the minimum of resistance to the air and yet to presenta plane surface to the ground below. So far as it went thisprotection was completely effective, but it failed to armour thevital parts against lateral, cross and downward fire while aloft. As the latter is more to be feared than the fire from the ground,seeing that it may be directed at point blank range, this was adecided defect and the armour was subsequently abandoned asuseless.

The only effective method of achieving the desired end is toarmour the whole of the carriage or fuselage of the adroplane,and this was the principle adopted by the Vickers Company. TheVickers military aeroplane is essentially a military machine. Itis built of steel throughout. The skeleton of the machine isformed of an alloy which combines the qualities of aluminium andsteel to ensure toughness, strength, and lightness. In fact,metal is employed liberally throughout, except in connection withthe wings, which follow the usual lines of construction. Thebody of the car is sheathed with steel plating which is bulletproof against rifle or even shrapnel fire. The car is designedto carry two persons; the seats are therefore disposedtandemwise, with the observer or gunner occupying the front seat.

The defensive armament is adequate for ordinary purposes. Beingfitted with a 100 horse-power motor, fairly high speeds areattainable, although the velocity is not equal to that ofmachines constructed upon conventional lines, inasmuch as thereis an appreciable increase in weight.

The car is short and designed upon excellent stream lines, sothat the minimum of resistance to the air is offered, while atthe same time the balancing is perfect. The sides of the car arebrought up high enough to protect the aviators, only their headsbeing visible when they are seated. The prow of the car followsthe lines generally adopted in high speed torpedo boat design;there is a sharp knife edge stem with an enclosed fo'c's'le, thelatter housing the gun.

Another craft, designed for scouting operations, may be likenedto the mosquito craft of the seas. This machine, while a biplanelike the military aeroplane, is of lighter construction,everything being sacrificed to speed in this instance. It isfitted with a 100 horse-power motor and is designed to carry anobserver if required. There is no offensive armament, however. The fuel tank capacity, moreover, is limited, being onlysufficient for a two or three hours' flight. While this isadequate for general reconnoitring, which for the most partentails short high speed flights, there are occasions when theStaff demands more prolonged observations conducted over agreater radius. This requisition can be met by eliminating theobserver, whose duties in this instance must be assumed by thepilot, and substituting in place of the former, a second fueltank of sufficient capacity for a flight of four or five hours,thereby bringing the term of action in the air to about 6 1/4hours. This machine travels at a very high speed and iseminently adapted to its specific duty, but it is of limitedservice for general purposes.

The arming of an aeroplane, to enable it to defend itself againsthostile attack or to participate in raiding operations upon theaerial fleet of the enemy, appears to be a simple task, but as amatter of fact it is an undertaking beset with difficultiesinnumerable. This is especially the case where the aeroplane isof the tractive type, that is to say where the propellers areplaced in the forefront of the machine and in their revolutionserve to draw the machine forward. All other considerations mustnecessarily be sacrificed to the mounting of the propeller. Consequently it is by no means easy to allot a position for theinstallation of a gun, or if such should be found there is graverisk of the angle of fire being severely restricted. In fact, inmany instances the mounting of a gun is out of the question: itbecomes a greater menace to the machine than to the enemy.

The French aeronautical section of the military departmentdevoted considerable study to this subject, but found the problemalmost insurmount able. Monsieur Loiseau met with the greatestmeasure of success, and his system is being practised in thepresent campaign. This principle is essentially adapted totractor aeroplanes. Forward of the pilot a special position isreserved for the gunner. A special mounting is provided towardsthe prow, and upon the upper face of the body of the machine. The gun mounting is disposed in such a manner that it is able tocommand a wide arc of fire in the vertical plane over the nose ofthe machine and more particularly in the downward direction.

The marksman is provided with a special seat, but when he comesinto action he has to stand to manipulate his weapon. The lowerpart of his body is protected by a front shield of steel plate, afifth of an inch in thickness, while a light railing extendingupon either side and behind enables the gunner to maintain hisposition when the aeroplane is banking and climbing. The machinegun, of the Hotchkiss type, is mounted upon a swivel attached toa tripod, while the latter is built into the bracing of the car,so as to ensure a fairly steady gun platform.

While the gun in the hands of a trained marksman may bemanipulated with destructive effect, the drawbacks to thearrangement are obvious. The gunner occupies a very exposedposition, and, although the bullet-proof shield serves to breakthe effects of wind when travelling at high speed which rendersthe sighting and training of the weapon extremely difficult, yethe offers a conspicuous target, more particularly when the enemyis able to assume the upper position in the air as a result ofsuperior speed in travelling. The gun, however, may be elevatedto about 60 degrees, which elevation may be accentuated by theinclination of the aeroplane when climbing, while the facilitywith which the weapon may be moved through the horizontal planeis distinctly favourable.

But the aerial marksman suffers from one very pronounced defect:he has a severely restricted survey of everything below, sincehis vision is interrupted by the planes. The result is that anenemy who has lost ascendancy of position is comparatively safeif he is able to fly immediately below his adversary: themitrailleuse of the latter cannot be trained upon him. On theother hand the enemy, if equipped with repeating rifles orautomatic pistols, is able to inflict appreciable damage upon thecraft overhead, the difficulties of firing vertically into the air notwithstanding.

In the Vickers system, where the propeller is mounted behind thecar, the aeroplane thus operating upon the pusher principle, thenose of the car is occupied by the arm, which is a rifle calibremachine gun fitted upon a special mounting. The prow is providedwith an embrasure for the weapon and the latter is so installedas to command an angle of 30 degrees on all sides of thelongitudinal axis of the machine when in flight. In thisinstance the marksman is provided with complete protection on allsides, inasmuch as his position is in the prow, where the hood ofthe fo'c's'le shields him from overhead attack. The gun isprotected by a special shield which moves with the gun barrel. This shield is provided with mica windows, through which thegunner is able to sight his arm, so that he is not inconveniencedin any way by the wind draught.

One shortcoming of such methods of arming an aeroplane will beobserved. Ahead firing only is possible; the weapon cannot betrained astern, while similarly the line of fire on eitherbroadside is severely limited. This is one reason why themachine-gun armament of aerial craft of the heavier-than-air typehas not undergone extensive development. In many instances thepilot and observer have expressed their preference for repeatinghigh velocity rifles over any form of fixed gun mounting, andhave recourse to the latter only when the conditions areextremely favourable to its effective employment.

Efforts are now being made to equip the military type ofaeroplane with both forward and astern firing guns. The urgencyof astern fire has been brought home very vividly. Suppose, forinstance, two hostile aeroplanes, A and B, are in the air. A hasthe advantage at first, but B is speedier and rapidly overhaulsA. During the whole period of the overhauling movement thegun of B can be directed upon A, while the latter, owing to thearc of training being limited to c d cannot reply. Obviously inthe running fight it would be to the advantage of B, although thefleeter machine, to keep behind A (position 1), but the latter ismaking towards its own lines.

Under these circumstances A must be headed off, so B crowds onspeed to consummate this end. But in the overtaking process Brenders his gun-fire ineffective, inasmuch as B passes beyond thearc of his gun which is represented by e f. But in so doing Bcomes within the firing arc of A (position 9). To minimise thisdanger B ascends to a higher level to obtain the paramountposition.

If, however, B were equipped with an astern gun the aeroplane Awould be within the fire of B when the forward gun of the lattercould not be used. Similarly if A were also fitted with anastern gun it would be able to attack its pursuer the wholetime B was to its rear and in this event, if its gun-fire weresuperior, it would be able to keep the latter to a safe distance,or compel B to manoeuvre into a superior position, which wouldentail a certain loss of time.

An astern firing gun would be valuable to B in another sense. Directly it had passed A or brought the latter within the zone ofits astern gun it could maintain its fire at the mostadvantageous range, because owing to its speed it would be ableto dictate the distance over which shots should be exchanged andif mounted with a superior weapon would be able to keep beyondthe range of A's guns while at the same time it would keep Awithin range of its own gun and consequently rake the latter. Inthe interests of self-preservation A would be compelled tochange its course; in fact, B would be able to drive it in anydirection he desired, as he would command A's movements bygun-fire.

The value of combined ahead and astern firing has beenappreciated, but there is one difficulty which at the momentappears to be insuperable the clearance of the propeller. At themoment astern-firing, if such it may be called, is maintained byrepeating rifles, but this armament is not to be compared withmachine-gun firing, as the latter with its capacity to pour 400to 600 shots a minute, is far more deadly, particularly when theweapon is manipulated by a crack gunner.

Up to the present the offensive armament of aeroplanes has beenconfined to light machine guns such as the Hotchkiss, Berthier,Schwartlose, and Maxim weapons. So far as the arming ofaeroplanes is concerned the indispensable condition is lightweight. With airships this factor is not so vital, the resultbeing that some dirigibles are mounted with guns, throwing onepound bursting shells, fitted either with delay action orpercussion fuses, the former for preference. These shells aregiven a wide cone of dispersion. Experiments are also being madewith a gun similar to the pom-pom which proved so useful in SouthAfrica, the gun throwing small shells varying from four to eightounces in weight at high velocity and in rapid succession. Whilesuch missiles would not be likely to inflict appreciable damageupon an armoured aeroplane, they would nevertheless bedisconcerting to the aviators subjected to such fire, and inaerial combats the successful undermining of the adversary'smoral is of far greater importance than in land operations, sinceimmediately ascendancy in the artillery operations is attainedthe final issue is a matter of moments.

But the most devastating arm which has yet been contrived foraerial operations is the light machine gun which has recentlybeen perfected. The one objective with this weapon is to disablethe hostile aircraft's machinery. It fires an armour piercingprojectile which, striking the motor of any aircraft, wouldinstantly put the latter out of action. The shell has a diameterof about .75 inch and weighs about four ounces. The gun is ahybrid of the mitrailleuse and the French "Soixante-quinze,"combining the firing rapidity of the former with the recoilmechanism of the latter. This missile has established itsability to penetrate the defensive armouring of any aeroplane andthe motor of the machine at 1,000 yards' range. This offensivearm is now being manufactured, so that it is likely to be seen inthe near future as the main armament of aeroplanes.

At the moment widespread efforts are being made in the directionof increasing the offensive efficiency of aircraft. It is one ofthe phases of ingenuity which has been stimulated into activityas a result of the war.

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