combined with the time fuse, the intention being to secure the explosion of the shell by impact should it hit the ground or other target sooner than was allowed for in the time setting.

As an account has already been given (Vol. IV., p. 371 et seq.) of the grenades and other hand-thrown missiles used in trench warfare, reference need be made here only to the bombs dropped from airships and aeroplanes. These are of two kinds-explosive and incendiary. One that was dropped in Paris by a German airman in May, 1915, may be taken as an example of the former, though the mechanical features of its design were but lightly esteemed by those who picked it up unexploded. It consisted of a cast-iron cylinder rather more than 4 inches long and about 1 inches in diameter, with rounded pieces attached at each end. The top carried a cone or vane of thick fabric intended to make the cylinder maintain itself in a vertical position during its fall. The interior was filled with trinitrotoluene, and the walls were weakened with external grooves to aid fragmentation. The exploding mechanism was contained in a brass tube about 2 inches in length fixed to the lower end of the cylinder, and consisted substantially of a striking rod which was

A

pushed up as its bottom end hit the ground or a building, a needle at its top end being then forced into the detonating material embedded in the high explosive of the bomb proper. heavy weight on the rod, aided by a spring, guarded the needle from being brought into premature contact with the detonator.

German incendiary bombs picked up in England and salved in a more or less damaged condition-one had been promptly dropped into a bucket of water-consisted, in one form, of a conical vessel about 10 inches in diameter at the base and over a foot in height. The body was made of metal pierced with holes and having an outer covering of an inflammable resinous material bound round with inflammable rope, which when ignited gave out a pungent smoke. Inside there was a mass of thermit, and generally some phosphorus in the base cup, while, as an additional luxury, celluloid chips and a little petrol were occasionally added. The igniting device and a handle were placed at the top. Thermit is the commercial name given to a patented mixture of granulated aluminium with some metallic oxide. When this mixture is ignited at one place a chemical reaction is started and spreads through the whole mass, the aluminium taking

After the foregoing survey of the different kinds of military ammunition we may turn to the engineering methods and processes employed for the production of the metal parts of shells and cartridges. Here only a general account is possible, for more than one reason. In the first place, a detailed description of all the methods adopted would be of interest only to professional engineers and would be unintelligible to anyone else. In the second place, an inordinate amount of space would be required, for it would be necessary to deal not only with the standard methods in use before the war began and with the various new arrangements which the makers of machine tools and other plant designed and brought forward, but also with the great number of what, without any disrespect, may be termed makeshift methods which hundreds of engineering manufacturers were forced to adopt in order to utilize their works. One of the most interesting features of the situation created by the war was indeed the manner in which plant and machinery designed for the manufacture of articles of peaceful commerce was adapted to the production of munitions. Examples might easily be multiplied, but three may be given from the western side of the Atlantic: one company whose normal occupation was the production of compressed air machinery was able to turn out large quantities of shrapnel with the addition of only one machine tool to its equipment; another in the course of a few months transformed its bridge and bridge girder shops into a shell factory; and the third made an arsenal out of works specially equipped for building railway locomotives and rolling stock.

The heaviest engineering operations in shell manufacture are those involved in the formation of the body or casing, and many of them can be performed in a variety of ways, sequences and groupings. The aim of the following account is to give a general idea of the character of the work and its results, and though it refers

mainly to the 18-pounder 3-3-in. shrapnel, it also applies in most respects to the larger calibres of the same type. Shrapnel shells are of special interest in that they possess a number of parts which are not required in armour-piercing and high explosive shells, but apart from these, and with due allowance for differences arising from size and function, the manufacture of the latter is broadly similar.

The 18-pounder shrapnel shell may be made from a solid bar of steel which is cut to a length about equal to that of the finished body and bored out internally by a drill, but forgings are generally regarded as preferable because, among other reasons, a smaller weight of metal

[British Fire Prevention Committee.

A GERMAN INCENDIARY BOMB. The external appearance is seen on the left. The interior contains thermit, a chemical mixture which when ignited produces a quantity of molten metal at a very high temperature.

-less than one half-is required. In the latter case the shell begins as a billet or block of steel 3 inches in diameter, and of a length perhaps half as much again. The first operation is to pierce this block and form it into a deep cup. For this purpose, after being heated in a furnace to about 2,000° F., it is quickly put into a die, and a shaped punch is forced into it by a hydraulic or power press. The result is that the metal is squeezed out round the punch, and when the block is removed from the die it possesses a round hole in its centre extending nearly to its base, and is lengthened to about 7 inches. The next process is to draw it out to still greater length; this again is effected in a press by means of shaped punches and dies working on the heated

metal, and it emerges, about 10 or 11 inches long, in a shape bearing a recognizable resemblance to its final form, though without a curved end. How close the resemblance should be is to some extent a matter of opinion. Some are in favour of making the dimensions approximate as nearly as possible to those required in the finished shell, so as to reduce to a minimum the amount of metal left to be cut away by the machine tools subsequently, while others hold that the more economical plan is to be content with a somewhat rough approximation to the final size in the forging process, and to leave a comparatively large amount of metal to be dealt with in the lathes.

However this question is settled, the forging has next to undergo a series of machining operations. After it has been cut to a length of 93 inches the body is rough-turned to size and the taper formed, the base end finished, the powder chamber bored out in the base, the nose end turned, and the recess with its waved ribs cut near the base to receive the copper driving band. At this stage in its production a number of its dimensions are gauged, and if it passes the ordeal satisfactorily it undergoes a heat treatment, which is a most important part of its manufacture if it is to behave properly when it is actually being fired out of the gun. The diaphragm that separates the bullets from the powder charge, the seat for which has already been prepared, is next dropped inside the shell, and the following operations include closing up the nose to the required curve and diameter, turning it, and cutting in its interior a screw thread to take the fuse socket. The closing up is performed by heating the nose to a dull red heat and forcing a coned die over it by means of a press. After this the body, and especially the nose, are finished either by turning in a lathe or by grinding, the latter being the newer method. The copper driving band is then slipped over the base of the shell, forced by some form of press into the groove already prepared for it, and turned to its final shape.

This completes the machining operations on the case itself, but a number of accessory parts remain to be added before the shell is ready for delivery. In the first place, the tin box which holds the charge of powder has to be placed in the powder chamber below the diaphragm. As the diaphragm was put into the shell at an earlier stage, before the closing-up process, because its diameter is too large to permit it to

The

pass the nose after the closing in of the latter, the tin box has to be jerked into position below it, and the operation requires some little dexterity. After it has been carried out and the two pieces have been driven home, the brass tube that is to convey the flash from the fuse in the head to the powder is screwed into a hole in the diaphragm, through which it protrudes into a hole in the upper part of the powder box. The next step is to fill the shell with bullets, which, by the turning of a tap, are run in from a receptacle like water. shell is meanwhile shaken by a mechanical device so that they may settle down properly, or sometimes they are rammed into place. To prevent them from moving and to fill up the interstices between them, molten rosin is poured in, and immediately afterwards the shell is weighed. The margin of error allowed from the standard weight is very small, but a slight deficiency may be made up by adding buckshot. The top of the powder tube is next soldered to the fuse socket, which must be screwed in before the rosin has set, the superfluous solder cleared away, and the tube cleaned out if necessary. A protecting plug, which will be removed when the fuse body is inserted, having been screwed into the fuse socket, the shell undergoes its final inspection, and if it passes muster is painted and packed with others into boxes for transport. The duty of putting the charge of powder in place does not fall on the manufacturer of the shells.

The two

As regards the manufacture of the accessory parts of the shrapnel, the powder chamber is formed of heavy tin plate in two pieces. The lower cup is cut out and formed to shape by means of a punch and die at a single operation, the rim being afterwards trimmed in a lathe. For the top part a blank is cut out from the sheet, its edges turned down, a hole pierced in the centre, and a small flang drawn round the hole, four operations being required. parts are then assembled and soldered together. The diaphragm, which in the finished shell is placed between the powder cup and the bullets, is made from a long strip of steel nearly half an inch thick. A circular disc is first punched out, and in subsequent operations, for which, as for the first, the metal is heated, is squeezed in dies to the required shape. The hole in the centre, into which the powder tube screws, is then drilled out, tapped and finished on lathes. Finally inspection follows, the requirements as to dimensions being fairly severe. At the other