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"=='AIR BOMBS==

Although the Hague declaration of Oct. 18 1907 contained a clause prohibiting, for a period extending till the next peace conference, the " discharge of projectiles and explosives from balloons or by other new methods of a similar nature," this declaration was only ratified by Great Britain, Austria-Hungary, the United States and Turkey. France, Germany, Italy, Japan, Russia and Spain did not sign it, and it was therefore regarded as " practically without force " (British official Land Warfare, 1912, p. 24). The only limiting condition of aerial bombardment was, therefore, that applying to all bombardments, viz.: The prohibition of bombardments of undefended localities. The word " undefended " was not more closely defined; and it could be, and by some far-seeing authorities was, presumed that aerial bombardment of localities would certainly figure as an element of the " next Great War." In the article AIR Defence will be found an account of the principles of defence against air bombardment, as they were evolved in the World War of 1914-8. The present article deals with the bombs themselves, as material weapons, and with their accessories.

Projectiles dropped from aircraft, officially termed "Aerial Bombs," may be classified as High Explosive Bombs (H.E. bombs), Incendiary Bombs, and Bomb Parachute Flares.

i. High Explosive Bombs

The principal use of H.E. bombs is to destroy material of all kinds; they are also used occasionally against personnel. They are a species of common shell, but differ from gun shells as, owing to the absence of shock of discharge, their envelopes require less strength, and consequently the proportion of weight of charge to weight of projectile is higher. With regard to their striking energy, bombs and gun shells, when fired at high angles, are comparable; but the striking energy of low-trajectory gun shells, other things being equal, is far beyond that of bombs dropped even from an extreme height. The field of action of a bomb is not restricted, as is that of a gun shell, by its extreme range, but depends upon the flying capacity of the aircraft employed; but the ballistic conditions under which a gun is used give an accuracy of fire which, in the case of bombs dropped from aircraft, is reduced to a minimum.

High explosive bombs are classified as Light Case and Heavy Case. Light case bombs, pear-shaped receptacles of mild steel, weighing when filled from 16 lb. to 100 lb., were made in great numbers in the early years of the World War. They were all of the same type. The case was made in two parts; the heavier, the nose end, was a hemispherical casting; the body was conoidal, tapering towards the tail end and the two parts were joined by an angle steel ring. In the 65-lb. bomb, for example, the nose end was. 25 in. and the body

064 in. thick. As time went on the type developed; fig. i shows a ??k???? ?.?? ????????

° =11?oi???%???1?? ?t11¦11l=11 230-lb. bomb made of mild steel, .128 in. thick in the body and increasing to

375 in. in the nose. It carries 140 lb. of 40/60 amatol.

FIG. I.

Light case bombs have practically no fragmentation and depend for effect on their charge alone. Heavy case bombs are made of single castings of steel or iron such as the heavy case 112-lb. bomb shown in fig. 2. Its cast-iron bod y varies from -5 in. to I in in thickness and it carries about 28 lb. of 80/20 amatol. The fragmentation of these bombs is of the highest importance.

Bombs are usually provided with a central tube running their whole length, fitting into screwed sockets for which the bomb is tapped at nose and tail, except when the bomb, like the light case 230-lb. bomb, is provided with a sharp nose, when a tail socket alone exists. This central tube is divided into two parts by a steel ring called the diaphragm for convenience in loading and keeping components in their place. In the heavy case 20-lb. and go-lb. bombs, the tail is prolonged outside the bomb proper by a light construction called a fairing, to provide a suitable shape for aerial flight. The 20-lb. bomb is peculiar in having only a nose socket and in the shape of its central tube. Lifting lugs are attached to many bombs. They are made of wrought iron and are riveted to the case so as to be in the same vertical plane as the centre of gravity of the filled bomb, when the latter is suspended in a horizontal position. At first bombs were released when horizontal; but now they are frequently suspended vertically from an eyebolt attached to the nose fuze or screwed into the nose socket. When a bomb is thus released it turns over in flight and falls nose first. Lifting bands of steel are sometimes used in place of lifting lugs. Four vanes or fins, placed in quadrature, are riveted to the case of all bombs about the tail end, to ensure steadiness in flight. The interiors of bombs are varnished or lacquered; they are then filled with high explosive.

High Explosives used in H.E. Bombs. - Trinitrotoluene, known as trot y l and T.N.T., is used as the main charge of a bomb or as a topping to a charge of amatol, which on account of its hygroscopic nature has to be protected from damp. T.N.T., when compressed into pellets, is also used in exploders and relays. Amatol is used as a main charge for bombs. It is a mixture of ammonium nitrate and T.N.T.; at first it consisted of 40 parts ammonium nitrate and 60 parts T.N.T. (40/60 amatol); later on, 80 parts ammonium nitrate and 20 parts T.N.T. (80/20 amatol) was the mixture adopted. Tetronitromethylaniline, known as tetryl, Composition Exploding or C.E., when compressed into pellets is used in exploders and relays. Fulminate of mercury is used for detonators.

Bomb Components

Bomb components consist of fuzes, exploders, relays, detonators and igniters. Those selected for a given purpose are called an assemblage. The assemblage varies with the bomb and the purpose for which it is to be employed; but in every case an H.E. bomb is detonated on impact by the action of the striker of a fuze, which explodes a cap or patch of cap composition, detonating a relay or exploder, which detonates the main charge of the bomb. Exploders are hollow cylinders of sheet brass or paper filled with compressed pellets of T.N.T. or C.E. They are provided at one or both ends with metal envelopes or sleeves for the reception of the particular detonator with which they are to be used. Exploders vary in length and other details. Relays are exploders of a special kind, usually filled with pierced C.E. pellets; the y are always next the fuze, to which they are sometimes attached by screwed thimbles called adapters. Detonators are copper tubes of various sizes and are charged with from 45 gr. to 60 gr. of fulminate of mercury according to the use for which they are intended. When they are to be fired b y a striker they are closed by a cap. Igniters are a special form of detonator, which carry between their charge and the cap a piece of match designed to cause a certain delay (up to 15 secs.) between the moment of impact of the bomb and its explosion. The match composition consists of nitrates and chlorates of potash, etc., mixed with shellac and methylated spirit.

Fuzes

Both nose and tail fuzes are provided for H.E. bombs. The former are all on the percussion principle and are usually called direct-acting fuzes (D.A. fuzes). The first to be used by the British was a modification of the No. 18 gun percussion fuze made for a tapered fuze hole. The motion of the striker, however, was controlled by a collar carrying two small vanes, called arming vanes. The vanes rotated as the bomb descended, eventually screwing the collar off the striker and leaving it free to act in the same way as it would in No. 18 after undergoing the shock of discharge when fired in a gun.

A tapered fuze hole being found an unnecessary refinement in the nose bushes of bombs, the latter were tapped cylindrically and fuzes with corresponding threads were adopted. The latest development is the D.A. pistol (see fig. 2) which is an ordinary percussion fuze fitted at the top with a cover to which the vanes are attached, as is also a hanging eyebolt for the suspension of the bomb. At the bottom end the fuse is attached by an adapter to a detonator and relay and the assemblage thus complete can be screwed into the bomb. In certain special nose fuzes the action of the vanes is utilized to screw the striker into position. Safety devices exist in all fuzes. Tail fuzes are all of that type to which the term pistol was originally given. (See figs. 1 and 2.) The striker at its upper end terminates in a screw upon which works a collar with vanes attached. As the bomb falls the collar screws off and releases the striker, which is then only held in position by a spiral spring; on impact this spring is compressed and the striker is forced down upon a cap which explodes the bomb. If desired, however, a match burning a certain number of seconds may be interpolated between the cap and the charge, thus forming an igniter which secures the desired delay action.

When a nose fuze is employed the striker is on impact driven on to a detonator which causes a practically instantaneous explosion; but all tail fuzes must of necessity have a slight delay, for they only act after the speed of the bomb has been reduced considerabl y by meeting with some serious resistance, and this results practically in a delay of at least a quarter of a second, which delay can, as already explained, be extended up to 15 secs. by the use of igniters. It is evident, therefore, that a bomb set in action by a nose fuze has no chance of penetrating a target before explosion takes place; there is but a small crater formed and fragments of the bomb are scattered over a wide area. A nose fuze, therefore, is used with heavy case bombs in the attack of personnel and light structures, such as aeroplanes in transit, where crater effect is not required. With tail fuzes, on the contrary, bombs falling in suitable ground will bury themselves before exploding, producing considerable craters but scattering no fragments. Tail fuzes in connexion with light case bombs are therefore employed in the attack of railways, dumps, buildings, and for general local destruction.

In the attack of certain buildings a combination of a nose and tail fuze is adopted. The shearing pin of the former is such as not to be broken as the bomb passes through the roof, while the tail fuze has a delay which will cause an explosion inside the building. If in such a case a tail fuze only were used, should the bomb break up on impact, the delay action might entail incomplete detonation or there might be no detonation at all. When bombs are made of cast iron both nose and tail fuzes are always employed.

Carriage of Bombs

Filled bombs are stored with all sockets, etc., plugged; components are packed in their own receptacles. Before the various detonators, relays, fuzes, etc., which constitute the assemblage, are inserted in the central tube of a bomb, the latter is tested in the dropping gear; when all is proved to be satisfactory the bomb is made " live "; but all safety devices are kept in operation till the moment of ascent. If a machine lands with bombs unexpended, all safety pins and other devices are made operative before the bombs are removed from the carrier.

Sighting of Bombs

If a machine be flown directly on a target at a known constant height and with a known constant speed, a sighting apparatus can be employed from which, however, accurate results cannot be expected. Its use depends upon the following theoretical considerations: a bomb, when released, will continue to travel with the velocity of the machine and will pass over a horizontal distance before striking earth, which will depend on this velocity and the time taken to fall from the height at which the machine is flying. If then a right-angled triangle be formed with an altitude equal to the given height and a base equal to the horizontal distance passed over by the bomb, the slope of the hypothenuse will give the direction of the line of sight which must be employed.

The sighting apparatus is fitted with a horizontal wire which acts as a foresight and with three other similar wires which act as backsights, each for a given speed and height. Thus an observer using the backsight will have his line of sight so directed that when it passes through the target he knows he must release the bomb.

The heights and speeds provided for are: a height of 6,000 ft. and a speed of 90 m. an hour; a height of 10,000 ft. and a speed of 80 m. an hour; a height of 15,000 ft. and a speed of 70 m. an hour. The foresight is capable of fore-and-aft movement by which corrections for wind and density of the air can be given. Two fore-andaft wires in the apparatus, placed vertically one over the other, serve in preserving the proper direction of flight.

Typical Bombs

The following are typical bombs for the purposes named: - The 20-lb. is a small heavy case bomb, capable of carriage by light machines; it is used in the attack of personnel, aerodromes and road transport. It is made of steel, its actual weight being 24 lb.; it will take a charge of 4 lb. 9 oz. of 40/60 amatol or 4 lb. of 80/20 amatol. The 50-lb. bomb is a medium heavy case bomb for general use especially against material, and can be carried by the smaller bombing machines on long-distance raids. Its actual weight is 491lb.; it carries a charge of io lb. 80/20 amatol; it is made of cast iron, 2 in. thick in the body and a' in. thick at the nose; the overall dimensions are 284 in. long by 7 in. maximum diameter. It is sometimes carried vertically slung from the eyebolt of the nose fuze, sometimes horizontally when it is attached to the dropping gear by means of a steel band. The 112 lb. bomb is a larger heavy case bomb (see fig. 2) used for similar purposes in larger machines. The 230-lb. bomb is a large light case bomb, used for crater production in the attack of railways and buildings (see fig. 1).

In addition to these types of bomb, special bombs have been designed for special purposes. Thus the 336-lb. bomb was designed to effect demolitions by the distribution of heavy fragments. It carried a bursting charge of 70 lb. of compressed T.N.T. and the body was built up of bulged segments of steel 1 in. at their thickest parts. The 180-lb. bomb was designed as an armour-piercing bomb. It consists of a pear-shaped steel case varying in thickness from

9 in. to 3.3 in. from tail to nose, being provided with a cap of mild steel on the same principle as a capped armour-piercing projectile for a gun, and carrying a bursting charge of 20 lb. of 40/60 amatol or T.N.T.

A light case 520-lb. bomb has also been made for crater production and for use against submarines. When used in the latter capacity it has a special fuze to obtain " depth-charge ' effect, a purpose for which the 65-lb. bomb was used in the early part of the World War. The actual weight of this bomb is 525 lb. and it carries 340 lb. of 40/60 amatol. There is also a heavy case 550-lb. bomb, with a body of cast steel varying from .75 in. to 1

5 in. in thickness; it carries 180 lb. of 40/60 amatol.

As carrying power is developed, bombs tend to become larger: thus in a recent professional lecture (see Journal of the Royal Artillery, March 1921) a bomb of 1,650 lb. was spoken of, and even heavier types may be seen in the near future.

2. Incendiary Bombs

In British bombs of present make the following compositions are used :--Thermalloy, which consists of 50 parts magnetic oxide of iron, 27 parts aluminium and 23 parts sulphur; thermite, which consists of 76 parts magnetic oxide of iron and 24 parts aluminium; phosphorus; carcass composition, which consists principally of ground saltpetre, to which is added ground sulphur, sulphide of antimony, black powder and powdered aluminium, mixed with powdered resin, tallow and turpentine. The special match composition for igniters in incendiary bombs is approximately 34% chlorate of potash, 30% iron filings, 5% each of powdered aluminium and nitrate of barium and 26% shellac and methylated spirit.

The following are typical incendiary bombs: - The modified carcass bomb is made of tin plate, its overall dimensions being 194 in. long by 5 in. maximum diameter. It is tapped at the tail for a pistol. It carries 34 lb. carcass and 134 lb. thermalloy composition, the total weight of bomb and pistol being 234 pounds. It has two lifting lugs and is carried horizontal. During the loading of this bomb a former is employed to preserve the necessary cavity for the reception of the firing arrangement which consists of the pistol, the special igniter and the adapter and its attachment. The special igniter consists of a 28-bore Eley cap fitted with a copper sleeve containing a strip of instantaneous fuze, and the adapter is a screwed ring socket to which is attached a nozzle-ended celluloid tube loaded with 5 gr. of match composition. On preparation for action the igniter is pushed into the adapter, the latter is screwed on to the pistol which is then screwed into the bomb.

The caseless incendiary bomb is made of thermalloy moulded over an iron framework; its overall dimensions are 27.8 in. by 5 in. (side of square of maximum section). The total weight of the bomb is about 30 lb. of which 241 lb. consist of thermalloy. The bomb can be stowed either in a vertical or horizontal position, and it is fired by a tail fuze and special igniter. It is fired in a similar manner to the modified carcass bomb, except that in addition to the pistol, special igniter and adapter, a length of instantaneous fuze is placed below the nozzle of the celluloid tube.

The baby incendiary bomb consists of three parts, the body, the cartridge and the cap or cover. The body is cylindrical and of thin plate tin, but is weighted at the bottom; in the centre of this weighted portion is placed a short pin or striker. A little above the latter are two suspending lugs for the cartridge, made, by partially cutting out two small portions of the plate on opposite sides of the body and bending them inwards so as to form a support. The cartridge, which is of the ordinary sporting shape, has a percussion cap in the centre of the base and rests on the two lugs. The cap or cover is domeshaped at the bottom, above which are three vanes with a circular disc on top of them. The assembled bomb weighs about 6 oz. and is about 6 in. long by I in. in diameter. The bomb is carried on the machine with the vaned cap downwards, but on release it turns over and falls with the vaned cap upwards. When falling from heights of over 30 ft. the lugs on which the cartridge rests are on impact sheared or bent sufficiently to permit it to set forward on to the striker, when the cap is exploded and the cartridge case ejected and the thermite ignited simultaneously. These bombs are always used in masses, and are packed in a special carrier which allows them to fall with a considerable spread; thus, to take a particular example, the 272 bombs packed in one form of carrier would, if released at a height of 5,000 ft., cover an area of 30 yd. by 80 yards. The carrier can be dropped complete if it is desirable to get rid of the bombs speedily, as in the case of a forced landing. With large bombing planes like the Handley Page, bombs can be distributed either by using several machines or by successive releases from a single machine. The small bombs provide a many-chance method of attack, which is not possible with the larger incendiary bombs, for with the latter a direct hit must be secured upon a combustible target and the chances are greatly against this combination being achieved. As, however, the small bombs descend in showers with a large spread and on impact further disperse their cartridges over the target area, the chances of a successful attack are considerable.

The - incendiary and smoke bomb can be either burst on impact to produce a smoke screen or burst in air for the attack of kite-balloons, etc. It is made of tin plate. 025 in. thick and carries 30 lb. of phosphorus. Its overall dimensions are 1 ft. 10.75 in. long by 8 in. maximum diameter. It is tapped at nose and tail and has a central tube for a burster containing C.E. pellets and black powder. When used for smoke production a D.A. pistol is screwed into the nose and the tail is plugged, but when an air burst is required the nose socket is plugged and a special time fuze is screwed into the tail socket. The bomb when burst in air spreads out a shower of burning phosphorus over a circle of some 250 yd. in diameter. The lumps of phosphorus slowly burn out in falling and about half are used up in the first 2,000 ft. from the point of burst. If the latter be 3,000 ft. above the target the bomb will be practically lost. The special time fuze employed, the Medgelly fuze, is set in action by a striker, normally held back by a spring in compression, which is released by a trigger when the bomb is dropped.

The Rankers Dart.

This dart, invented by Engr.-Com. F. Ranken, was used for the attack of Zeppelins and for other purposes. It consisted of a hollow tin cylinder, about the size of a large candle; the bottom was closed by a pointed bullet of steel or iron, and its top by a lid of tin through which passed a spindle capable of vertical movement and terminating at the end outside the dart in four flanges or vanes. The cylinder was filled with incendiary composition which was fired after the fashion of a Christmas cracker. For this purpose a strip of friction match had one end attached to the cylindrical body and the other to the spindle. Then if the dart fell upon a Zeppelin from above, its sharp bullet point would enable it to penetrate the outer covering upon which, however, the four flanges or vanes would catch; a jerk would thus be given to the spindle causing the match to be torn apart and ignited, and the dart, held fast in the cover of the Zeppelin, would burst into flames.

3. Bomb Parachute Flares

These flares are used for reconnaissance at night, for illuminating and showing up ground held by the enemy, and for affording light to a pilot wishing to land in the dark. The flares are cylindrical paper tubes filled with aluminium composition and primed with magnesium composition; they are sometimes called candles. They are lighted by means of pieces of quickmatch attached to the primed end, the other end being fixed in a cup arrangement which is attached by a wire rope to the parachute.

Electric-Ignition Parachute Flare-Bombs are of two kinds almost similar in construction. One is used as a reconnaissance flare, the other as a landing flare to enable pilots to land in the dark. They are both launched by means of a launching tube attached to the fuselage of the aeroplane, and so designed that as the bomb leaves the launching tube an electric circuit is completed, and a platinum-silver wire bridge heated. This, by igniting a priming, sets a delay pellet in action and, after the bomb has dropped some 1,000 ft., a powder puff is fired, which both ignites the candles and projects the parachute clear of the cylinder. The reconnaissance flare (with a 9 seconds' delay pellet) burns for three to four minutes, weighs 6 lb. 13 oz., and has a parachute weighing i t oz. and measuring about 5 ft. 6 in. across when open. The landing flare weighs 5 lb. 41 oz., and has a parachute of the same size as the other but of lighter material, weighing only 31 oz. The candles burn for from 21 to 31 min., and the delay pellet only gives one sec. dela y so that the bomb opens after it has dropped some 20 feet. In both bombs the candle power is about 40,000. (J. R. J. J.) German Air Bombs. - The general characteristics of air bombs being the same in all countries, British practice may be regarded as typical and foreign bombs need not be dealt with. Some notes on German air bombs are added, however, on account of the special interest attaching to these projectiles, which for the first time for many centuries brought war to the very doors of the British people.

The earliest types designed by the Germans were so far ineffective that as early as the spring of 1914 they were replaced by bombs of a type known as " Carbonite." These bombs, which were used throughout the earlier part of the war, were pear-shaped and solid, pointed, and had a propeller-actuated pistol of the same type as those described earlier in this article. Their special characteristic was the form of air-drag used: instead of fins, a sort of inverted tin cap was used, attached to the tail of the bomb by stays. The smallest of these bombs weighed 41 kgm. (about 10 lb.), and the heaviest 50 kgm. (i 10 lb.). Small incendiary bombs of the carbonite type were also used. There was, further, a grenade-like projectile thrown by hand, which weighed 800 grammes (14 lb.), but this was criticized as being too small to be effective, as also was the 41 kgm. H. E. carbonite bomb.

In 1916, these bombs were replaced by a different type known as " and W.," which continued in use to the end of the war. They were torpedo-shaped 1 and were fitted with slanting vanes which not only acted as an air-drag to keep the projectile nose down but also imparted rotation to the falling bomb, and so enabled the German designers to replace the propeller as an arming device by centrifugal bolts, on the same principle as those of gun fuzes. As the height at which bombs were released had by that time greatly increased, the additional time required for the arming of the fuze was of no importance. Time fuzes were also employed, chiefly for obtaining delay effects after impact.

The standard sizes of these " P. and W." bombs were the 121 kgm. (27 lb.) - a thick-walled bomb with instantaneous fuze - and the 50, 100, 300 and 1,000 kgm. " mine " or thin-walled bombs, with bursters respectively of 23 kgm., 60 kgm., 180 kgm., and 680 kgm.

One other form of air projectile should be mentioned as, although it was never used on any large scale, it had a moment of notoriety 1 Torpedo-shaped bombs were also used by the French, who named them " pisciforme " (fish-shaped) bombs, in contradistinction piroforme " (pear-shaped).

in the early stages of the war. This was the dart, a heavy bullet of steel sharpened to a point at one end. These darts, released in showers, were intended to be effective against personnel.

(C. F. A.)