The Sun.
London, England, 1866-05-23 00:00:00

Naval and Military Intelligence.

The Ordnance vessel Helena, Mr. Moore com-
mander, on Monday conveyed to the main sheers of
Portsmouth dockyard a monster piece of ordnance
for experimental service on the works now erecting
around Southsea Castle, for the defence of the en-
trance to the channel leading into Portsmouth har-
bour from Spithead. The iron carriage and slide for
mounting the gun were forwarded with it in the
Helena, from Woolwich. The gun is coil, or Arm-
strong built, has a 13-inch diameter of bore, is rifled
on the Woolwich system, and weighs 23 tons. It is
15ft. 6in. in length, has a circumference of lift.
Bin. at the longest part of the breech, and a diame-
ter of 6ft. 6in. from one extreme of trunnion to the
other. The new lines of fortification, on part of
which this immense piece of ordnance is to be
mounted, will form, when completed, the key of
the sea defences of Portsmouth harbour, and having
been designed expressly to beat off the assault of any
hostile ironclad fleet, will necessarily be very for-
midable. The whole work, as designed; comprises
a central keep, with a battery to the right and left
of heavy earthworks carrying iron-shielded embra-
sures in granite frames. When completed the work
will supersede the stone fortifications of Southsea
Castle, erected during the reign of Henry
but rebuilt in 1814 under the supervision of Major-
Gen. Fisher, R.E.., and its auxiliary earthen batte-
ries. The glacis of the new work is washed by the
sea at high water. It stands on the southernmost
point of-Southsea-common beach line, the centre of
the work being at the apex of an obtuse angle, with
the coast line tending backward from it right and
left. It commands the entrance to Portsmouth
harbour channel from the sea and Spithead, the
channel being narrowed by the shoals so as only to
permit of the passing of one vessel at a time be-
tween them and the shore fortifications. The length
of the channel from the throat of the harbour at
Blockhouse fort to the Spit Shoal fort at the southern
end, or commencement of the entrance channel, is
20 cables in a line parallel with Southsea-common
beach, the distance from Blockhouse to the centre
of the new work of Southsea being about 13 cables,
and the breadth of water between the apex of the
work and the Spit fort, which all vessels, large or
small, must pass round to enter the harbour chan-
nel, being about six cables' length. These distances
will give some idea of the important part which the
new work must play in any future defence of the
harbour and dockyard of Portsmouth from attack
from seaward. The centre of the work is still oc-
cupied by the ancient stone tower of Henry VIII.'s
time. It is mounted with four 8-inch smooth-bore
guns, but is ordered to be dismantled as soon as the
exact form of the new keep has been decided upon.
At one period during the progress of the works it
-was-proposed to orvwn the uld stone Reep--wrth an
iron cupola on Captain Coles's plan, but this idea
has now been abandoned owing to the evident
weakness of the square tower and its incompetency
to support a cupola and its guns of sufficient weight
engage and defeat ironclad ships of war. Such a
structure is subject to the same conditions as are
attached to the design and construction of the
marine forts at Spithead—it should not be erected
for present necessities only, but as far as may be
possible as a work for all time. For these reasons
it is now contemplated to level the old stone work
to its foundation, and, with its granite material, to
build up a solid foundation for an iron cupola to
mount guns of not less calibre than the one brought
to Southsea and now about to be mounted experi-
mentally on the west earthen battery of the work.
The details of this cupola have not yet been fully
decided upon, but its design, it is understood, will
be sufficiently comprehensive to mount four of
these immense guns. The cupola will be revolv-
ing, like the turrets on board the Royal Sovereign,
and with a small steam engine to work it its move-
ment can always be continued in one direction,
its guns loaded when turned away from the enemy,
and each gun fired as it is brought to bear apon
the enemy by the cupola's revolutions. All this
yet remains to be accomplished. The earthern
batteries, however, which will form the right and
left flank of the cupola keep are all complete now,
with the exception of the iron shields to their em-
brasures and the laying down of the metal radial
ways for training the guns on their platforms. The
entire line of earthen rampart is in excess of 1,600
feet, 1,100 of which forms the battery west
of the keep and along the line of the harbour
channel, parallel with Southsea beach, and the re-
mainder east of the keep, and commanding the shoals
and the outer deep water at the channel entrance.
A mortar battery on each flank of the keep at the
junction of the earthworks has been prepared for
mounting each two of the heaviest of this class of
ordnance. The east battery will mount 11 guns and
the west battery 21, none of which will be less than
12 tons each in weight. All of these guns, which,
from their position, are exposed to a direct fire from
seaward, will be fought through iron shields fixed
between the granite piers of their embrasures, each
of these shields will be made of rolled iron armour-
plates 13in. in thickness, 12ft. in width by Bft. in
height, and will be strengthened further on the inner
side by siin. crossed iron frames, to which the ar-
mour-plates will be secured by bolts and nuts in the
usual way. The shields will have a slight incline
towards the interior of the work of 41in. from their
base, and will be held in position by side struts of
iron and cross tail pieces of enormous strength. The
gunport in each shield will measure 3ft. 6in. by 2ft.
The earthen ramparts to carry all this mass of super-
incumbent metal in shields, guns, carriages, and their
slides, have been built of unusual dimensions, and
strengthened in every way with granite, brick, and
concrete. The thickness of the earth at the narrowest
part of their base line is 108 ft. The middle of the
terre-plein is 27ft. 6in., and of the merlon 29ft. 6in.
—the total thickness of earth at the gun platformbeing
no less than 57ft. in the weakest parts. The distance
from centre to centre of the gun shields averages
55ft. The camp stands a good height above the terre
plein, and the garrison will be fully protected from
all seaward danger, excepting vertical fire. To every
two guns are provided expense and shell magazines
along the faces of the batteries, and on the flanks of
the batteries the magazine provision is still more
extensive. On the extreme of the west battery, where
it might become, under certain exceptional condi-
tions, exposed to a flanking fire from long, range
guns, the six guns mounted there are thoroughly
protected from the effects of such a contingency by
massive earthen traverses. The two main magazines
one in each battery at the bass of the rampart, are
each large and massively constructed buildings, but
standing on-the level of the parade ground. Their
powder bays have each a stowage capacity for 750
barrels of powder, and a wing passage entirel yround
the magazine walls gives uninterrupted means of
ingress and egress to the cartridge to and from the
batteries. The brickwork to the covering arches of
the magazines is 3ft. in thickness on the crowns, sue-