perfect workmanship was required in the formation of the barrel and the
shots, the expense attending their manufacture and use was much greater
than that incurred in the case of the Armstrong guns. Sir W. Armstrong’s
estimate for a 35–ton gun was £3,500, and Sir J. Whitworth’s, £6,000.
The gun, as constructed at Woolwich on Mr. Fraser’s plan, was estimated
to cost £2,500. The first cost of a gun is a matter for consideration,
since each piece, even the strongest, is able only to fire a limited
number of rounds before it becomes unsafe or useless. It appears that no
cannon has yet been constructed capable of withstanding without
alteration the tremendous shocks given by the explosion of the
gunpowder, and these alterations, however small at any one discharge,
are summed up and ultimately bring to an end what may be termed the
“life of the piece.”
[Illustration:
FIG. 92.—_600–pounder Muzzle-loading Armstrong Gun._
]
About the year 1858 Sir William Armstrong (afterwards Lord Armstrong)
established at Elswick, Newcastle-on-Tyne, a manufactory of ordnance,
which has since developed into the great arsenal now so well known all
over the world. Here all the resources of science have been applied to
the problems of artillery, and experiments carried on with a prodigality
of cost and promptness of execution impossible at a government
establishment trammelled with official regulations. Here, and also at
Woolwich, our national ordnance factory, guns have since always been
constructed on the building-up plan advocated by Sir W. Armstrong, whose
principle consists in disposing of the fibre of the iron so as best to
resist the strains in the several parts of the gun. Wrought iron being
fibrous in its texture has, like wood, much more strength in the
direction of the grain than across it. The direction of the fibre in a
bar of wrought iron is parallel to its length, and in that direction the
iron is nearly twice as strong as it is transversely. A gun may give way
either by the bursting of the barrel or by the blowing out of the
breech. The force which tends to produce the first effect acts
transversely to the axis of the gun; hence the best way to resist it is
to wrap the iron round the barrel, so that the fibres of the metal
encircle it like the hoops of a cask. The force which tends to blow out
the breech is best resisted by disposing the fibres of the iron so as to
be parallel to the axis of the gun; hence Sir W. Armstrong makes the
breech-piece from a solid forging with the fibre in the required
direction. But the Elswick building-up principle involves much more than
the direction of the fibres of the iron, for each coil or jacket, after
having its spires welded together, was bored out on a lathe, and the
exterior of the part of the gun on which it was to be placed was also
turned with the utmost exactness, so that when the enveloping piece was
heated to a certain temperature and in this state brought into position,
it would in cooling compress the parts it encircled just to that degree
which careful calculations showed would best strengthen the gun without
unduly straining the metal at any part. The Elswick guns being built up
of several superimposed jackets of calculated lengths and thicknesses,
the means was afforded of distributing the tensions throughout the whole
mass of metal to the best advantage. In the simpler form, arranged by
Mr. Fraser, and for the sake of economy adopted by the authorities at
Woolwich in 1867, the greater part of the benefit derivable from
adjustment of tension was no doubt sacrificed to cheapness of
manufacture. These, and also the forms of Armstrong guns that have not
yet been described, ceased to be made after 1880, by which time steel
had replaced iron in every part of the construction and fittings of
guns, and muzzle-loading had been definitely abandoned in favour of
breech-loading.
[Illustration:
FIG. 93.—_35–ton Fraser Gun._
]
Now, in 1874, when the first edition of the present work was in
preparation, the Fraser-Woolwich guns were in full vogue, being spoken
of by the public press as the _ne plus ultra_ of artillery construction
in size, efficiency, and economy. When, accordingly, the author had been
privileged to visit the arsenal and witness the production of these guns
in every stage of their manufacture, he wrote a description of it which
is here retained as printed at the time, seeing that it may not be
without historical interest, particularly since great numbers of these
guns must still be extant, mounted on our forts in various parts of the
world, and seeing also that the description of the simpler formations
may render more easily to be understood future references to similar
operations in gun-making as have been retained in the later
developments. Of course, the following description was written in the
_present tense_, and therefore in perusing it the reader must constantly
bear in mind that the guns with which our ships of war have since been
equipped are in _every respect entirely different_ from
_The Fraser-Woolwich Guns, 1867–1880._
[Illustration:
FIG. 94.—_Section of 9 in. Fraser Gun._
]
Until the year 1867 the guns made at Woolwich were constructed according
to the original plan proposed by Sir W. Armstrong, and on this system
one of the large guns consisted of as many as thirteen separate pieces.
These guns, though unexceptionable as to strength and efficiency, were
necessarily so very costly that it became a question whether anything
could be done to lessen the expense by a simpler mode of construction or
by greater economy in the material. The problem was solved in the most
satisfactory manner by Mr. Fraser, of the Royal Gun Factory, who
proposed an important modification of the original plan, and the
adoption of a kind of iron cheaper than had been previously employed,
yet perfectly suited for the purpose. Mr. Fraser’s modification
consisted in building up the guns from only a few coils, instead of
several, the coils being longer than Sir W. Armstrong’s, and the iron
coiled upon itself two or even three times: a plan which enabled him to
supersede the breech-piece, formerly made in one large forging, by a
piece formed of coils. In order to perceive the increased simplicity of
construction introduced by Mr. Fraser, we need but glance at the section
of a 9 in. gun constructed according to his system, Fig. 94, and
remember that a piece of the same size made after the original plan had
ten distinct parts, whereas the Fraser is seen to have but four. Compare
also Figs. 92 and 93. We shall now describe the process of making the
Fraser 9 in. gun. The parts of the gun as shown in the section, Fig. 94,
are: 1, the steel barrel; 2, the B tube; 3, the breech-coil; 4, the
cascable screw. The inner steel barrel is made from a solid cylinder of
steel, which is supplied by Messrs. Firth, of Sheffield. This steel is
forged from a cast block, the casting being necessary in order to obtain
a uniform mass, while the subsequent forging imparts to it greater
solidity and elasticity. After the cylinder has been examined, and the
suitable character of the steel tested by trials with portions cut from
it, the block is roughly turned and bored, and is then ready for the
toughening process. This consists in heating the tube several hours to a
certain temperature in an upright furnace, and then suddenly plunging it
into oil, in which it is allowed to remain for a day. By this treatment
the tenacity of the metal is marvellously increased. A bar of the steel
1 in. square previous to this process, if subjected to a pull equal to
the weight of 13 tons, begins to stretch and will not again recover its
original form when the tension is removed, and when a force of 31 tons
is applied it breaks. But the forces required to affect the toughened
steel in a similar manner are 31 tons and 50 tons respectively. The
process, unfortunately, is not without some disadvantages, for the
barrel is liable to become slightly distorted and even superficially
cracked. Such cracks are removed by again turning and boring; the
hardness the steel acquires by the toughening process being shown by the
fact that in the first boring 8¼ in. diameter of _solid_ steel is cut
out in 56 hours, yet for this slight boring, in which merely a thin
layer is peeled off, 25 hours are required; and lest there should be any
fissures in the metal, which, though not visible to the eye, might make
the barrel unsound, it is filled with water, which is subjected to a
pressure of 8,000 lbs. per square inch. If under this enormous pressure
no water is forced outwards, the barrel is considered safe. It is now
ready to have the B tube shrunk on it.
The B tube, like certain other portions of these guns, is constructed
from coiled iron bars, and this constitutes one great peculiarity of Sir
W. Armstrong’s system. It has the immense advantage of disposing the
metal so that its fibres encircle the piece, thus applying the strength
of the iron in the most effective way. The bars from which the coils are
prepared are made from “scrap” iron, such as old nails, horse-shoes, &c.
A pile of such fragments, built up on a wooden framework, is placed in a
furnace and intensely heated. When withdrawn the scraps have by
semi-fusion become coherent, and under the steam hammer are soon welded
into a compact mass of wrought iron, roughly shaped as a square prism.
The glowing mass is now introduced into the rolling-mill, and in a few
minutes it is rolled out, as if it were so much dough, into a long bar
of iron. In order to form this into a coil it is placed in a very long
furnace, where it can be heated its entire length. When sufficiently
heated, one end of the bar is seized and attached to an iron core of the
required diameter, and the core being made to revolve by a steam engine,
the bar is drawn out of the furnace, winding round the core in a close
spiral, so that the turns are in contact. The coil is again intensely
heated, and in this condition a few strokes of the steam hammer in the
direction of its axis suffice to combine the spires of the coil into one
mass, thus forming a hollow cylinder.
The B tube for the 9 in. gun is formed of two double coils. When the two
portions have been completely welded together under the steam hammer,
the tube, after cooling, is roughly turned and bored. It is again fine
bored to the required diameter, and a register of the diameter every few
inches down the bore is made. These measurements are taken for the
purpose of adapting most accurately the dimensions of the steel barrel
to the bore of the B tube, as it is found that perfect exactness is more
easily obtained in turning than in boring. The steel barrel is therefore
again turned to a size slightly _larger_ than the bore of the B tube,
and is then placed muzzle end upwards, and so arranged that a stream of
water, to keep it cool, shall pass into it and out again at the muzzle,
by means of a syphon, while the B tube, which has been heated until it
is sufficiently expanded, is passed over it and gradually cooled.
If now the B tube were allowed to cool spontaneously, its ends would, by
cooling more rapidly than the central part, contract upon the steel
barrel and grip it firmly at points which the subsequent cooling would
tend to draw nearer together longitudinally, and thus the barrel would
be subjected to injurious strains. In order to prevent this, the B tube
is made to cool progressively from the breech end, by means of jets of
water made to fall upon it, and gradually raised towards the muzzle end,
which has in the meanwhile been prevented from shrinking by having
circles of gas-flames playing upon it.
The breech-coil, or jacket, is formed of three pieces welded together.
First, there is a triple coil made of bars 4 in. square, the middle one
being coiled in the reverse direction to the other two. After having
been intensely heated in a furnace for ten hours, a few blows on its end
from a powerful steam hammer welds its coils perpendicularly, and when a
solid core has been introduced, and the mass has been well hammered on
the sides, it becomes a compact cylinder of wrought iron, with the
fibres all running round it. When cold it is placed in the lathe, and
the muzzle end is turned down, leaving a shoulder to receive the
trunnion-ring. The C coil is double, welded in a similar manner to the B
coil, and it has a portion turned off, so that it may be enclosed by the
trunnion-ring.
The trunnion-ring is made by punching a hole in a slab of heated iron
first by a small conical mandrel, and then enlarging by repeating the
process with larger and larger mandrels. The iron is heated for each
operation, and the trunnions are at the same time hammered on and
roughly shaped—or, rather, only one has to be hammered on—for a portion
of the bar which serves to hold the mass forms the other. The
trunnion-ring is then bored out, and after having been heated to
redness, is dropped on to the triple breech-coil which is placed muzzle
end up, and the turned end of the C coil (of course, not heated) is then
immediately placed within the upper part of the trunnion-ring. The
latter in cooling contracts so forcibly as to bind the ends of the coils
together, and the whole can thus be placed in a furnace and heated to a
high temperature, so that when removed and put under the steam hammer,
its parts are readily wielded into one mass. The breech-coil in this
state weighs about 16 tons; but so much metal is removed by the
subsequent turnings and borings, that it is reduced to nearly half that
weight in the gun. It is then turned in a lathe of the most massive
construction, which weighs more than 100 tons. Fig. 34, page 95, is from
a drawing taken at Woolwich, and shows one of the large guns in the
lathe. No one who witnesses this operation can fail to be struck with
the apparent ease with which this powerful tool removes thick flakes of
metal as if it were so much cheese. The projections of the trunnions
prevent the part in which they are situated from being finished in this
lathe, and the gun has to be placed in another machine, where the
superfluous metal of the trunnion-ring is pared off by a tool moving
parallel to the axis of the piece. Another machine accomplishes the
turning of the trunnions, the “jacket” being made to revolve about their
axis. The jacket is then accurately bored out with an enlargement or
socket to receive the end of the B tube, and a hollow screw is cut at
the breech end for the cascable.
The portion of the gun, consisting of the steel barrel with the B tube
shrunk on it, having been placed upright with the muzzle downwards, the
breech-piece, strongly heated, is brought over it by a travelling crane,
and slips over the steel barrel, while the recess in it receives the end
of the B tube. Cold water is forced up into the inside of the barrel in
order to keep it cool. As the breech cools, which it is allowed to do
spontaneously, it contracts and grips the barrel and B tube with great
force. The cascable requires to be very carefully fitted. It is this
piece which plays so important a part in resisting the force tending to
blow out the end of the barrel. The cascable is a solid screw formed of
the very best iron, and its inner end is wrought by scraping and filing,
so that when screwed in there may be perfect contact between its face
and the end of the steel barrel. A small annular space is left at the
circumference of the inner end, communicating through a small opening
with the outside. The object of this is, that in case of rupture of the
steel barrel, the gases escaping through it may give timely warning of
the state of the piece.
Besides minor operations, there remain the important processes of
finishing the boring, and of rifling. The boring is effected in two
operations, and after that the interior is gauged in every part, and
“lapping” is resorted to where required, in order to obtain the perfect
form. Lapping consists in wearing down the steel by friction against
fine emery powder and oil, spread on a leaden surface. The piece is then
ready for rifling. The machinery by which the rifling is performed
cannot be surpassed for its admirable ingenuity and simplicity.
In this operation the gun is fixed horizontally, its axis coinciding
with that of the bar, which carries the grooving tools. This bar is
capable of two independent movements, one backwards and forwards in a
straight line in the direction of the length of the bar, and the other a
rotation round its axis. The former is communicated by a screw parallel
to the bar, and working in a nut attached to the end of it. For the
rotatory movement the bar carries a pinion, which is engaged by a rack
placed horizontally and perpendicularly to the bar, and partaking of its
backward and forward movement, but arranged so that its end must move
along another bar placed at an angle with the former. It is this angle
which determines the pitch of the rifling, and by substituting a curved
guide-bar for the straight one, an increasing twist may be obtained in
the grooves.
The projectile used with these guns is of a cylindrical form, but
pointed at the head, and the moulds in which these shots are cast are so
arranged that the head of the shot is moulded in iron, while the body is
surrounded with sand. The rapid cooling induced by the contact of the
cold metal causes the head of the shot to solidify very quickly, so that
the carbon in the iron is not separated as in ordinary casting. In
consequence of this treatment, the head of the shot possesses the
hardness of steel, and is therefore well adapted for penetrating iron
plates or other structures. The projectiles are turned in a lathe to the
exact size, and then shallow circular cavities are bored in them, and
into these cavities brass studs, which are simply short cylinders of a
diameter slightly larger than the cavities, are forced by pressure. The
projecting studs are then turned so as accurately to fit the spiral
grooves of the guns. Thus the projectile in traversing the bore of the
piece is forced to make a revolution, or part of a revolution, about its
axis, and the rapid rotation thus imparted has the effect of keeping the
axis of the missile always parallel to its original direction. Thus
vastly increased accuracy of firing is obtained.
[Illustration:
FIG. 95.—_Millwall Shield after being battered with Heavy Shot.—Front
View._
]
[Illustration:
FIG. 96.—_Rear View of the Millwall Shield._
]
Shells are also used with the Woolwich rifled guns. The shells are of
the same shape as the solid shots, from which they differ in being cast
hollow, and having their interior filled with gunpowder. Such shells
when used against iron structures require no fuse; they explode in
coming into collision with their object. In other cases, however, the
shells are provided with fuses, which cause the explosion when the shot
strikes. Fig. 93, page 195, represents one of the 35–ton guns, made on
the plan introduced by Mr. Fraser. This piece of ordnance is 16 ft.
long, 4 ft. 3 in. in diameter at the breech, and 1 ft. 9 in. at the
muzzle. The bore is about 1 ft. Each gun can throw a shot or bolt 700
lbs. in weight, with a charge of 120 lbs. of powder. It is stated that
the shot, if fired at a short range, would penetrate a plate of iron 14
in. thick, and that at a distance of 2,000 yards it would retain
sufficient energy to go through a plate 12 in. thick. The effect of
these ponderous missiles upon thick iron plates is very remarkable.
Targets or shields have been constructed with plates and timber backing,
girders, &c., put together in the strongest possible manner, in order to
test the resisting power of the armour plating and other constructions
of our ironclad ships. The above two cuts, Figs. 95 and 96, are
representations of the appearance of the front and back of a very strong
shield of this description, after having been struck with a few 600 lb.
shots fired from the 25–ton gun. The shots with chilled heads, already
referred to, sometimes were found to penetrate completely through the 8
in. front plate, and the 6 in. of solid teak, and the 6 in. of plating
at the back. The shield, though strongly constructed with massive plates
of iron, only served to prove the relative superiority of the artillery
of that day, which was at the time when our century had yet about thirty
years to run. Up to 1876 no confidence was placed in steel as a
resisting material, a circumstance perhaps not much to be wondered at,
as its capabilities had not then been developed by the newer processes
of manufacture, described in our article on Iron; nor had mechanicians
acquired the power of operating with large masses of the metal. Since
then it has come about that only steel is relied upon for efficiently
resisting the penetration of projectiles, iron being held of no account
except as a backing. There has always been a rivalry between the
artillerist and the naval constructor, and this contest between the
attacking and the defending agencies is well illustrated in the table on
page 166, where the parallel advance in the destructive power of guns
and in the resisting power of our war-ships is exhibited in a numerical
form.
[Illustration:
FIG. 97.—_Comparative Sizes of 35 and 81 ton Guns._
A, 35–ton; B, 81–ton.
]
The 35–ton Fraser guns were at the time of their production humorously
called in the newspapers “Woolwich infants”; but it was not long before
they might in another sense be called infants in comparison with a still
larger gun of 81 tons weight constructed at Woolwich shortly before
iron-coiling and muzzle-loading were set aside. Fig. 97 shows the
relative dimensions of the 35–ton and 81–ton guns: the latter was built
up in the same way as the 9–inch gun described above, but the coils were
necessarily longer and the chase was formed in three parts instead of
two. The total length of this gun was 27 feet, and the bore was about 24
feet long and 14 in. in diameter, and the weight of the shot about 1000
lbs., with sufficient energy to penetrate at a considerable distance an
iron plate 20 in. in thickness. It was for the manufacture of these very
large guns that the great steam hammer, represented in Plate III., was
erected at Woolwich.
* * * * *
The 81–ton gun was the largest muzzle-loader ever made in the national
gun factory at the time when such huge weapons were in request; but in
1876 its dimensions were surpassed by those of a few 100–ton guns built
at Elswick to the order of the Italian Government for mounting on their
most formidable ironclads. These guns have a calibre of 17·72 inches,
and are provided with a chamber of somewhat larger bore to receive the
charge of powder. They are built up on the Armstrong shrinkage
principle, and comprise as many as twenty different tubes, jackets,
hoops, screws, etc., and are undoubtedly the most powerful
muzzle-loading weapons ever constructed. It happened, just as these guns
were completed, that the British Government, apprehensive at the time of
a war with Russia, exercised its rights of purchasing two of them, one
to be mounted at Gibraltar, the other at Malta.