ARMOURED DEFENCES. 
339 
This fort occupies a site at the end of the Breakwater at Portland. 
Its foundations rest on a clay bottom about 10 fathoms below low 
water mark. The battery is circular (radius about 58 ft.), and its floor 
is about 23 ft. above high water mark. It is to mount fourteen 38-ton 
guns. The gun ports are 23 ft. 4 ins. from centre to centre. 
With regard first to the inner structure and roof of the battery, this 
consists, generally speaking, of two strong rings of box-girder construc¬ 
tion going all round the battery, one at the level of the floor, and the 
other at the level of the roof, against which the armoured wall rests. 
The remainder of the inner or supporting structure consists of strong 
iron pillars, in couples, between the ports, which carry a ring of solid 
armour bars round the entire battery to form the front support of a 
bomb-proof iron roof. The rear of this roof is supported on a ring 
of box-girders resting on masonry piers. 
The armoured wall consists of three thicknesses of 6i-in. plates, with 
port frames, 2Jins, thick, round the ports. 
Spitbank Fort, which is the innermost of the Spithead Forts, is of 
similar construction to Portland Breakwater Fort, except as to form 
and size. 
The iron battery mounts nine 38-ton guns, and occupies the outer 
or seaward side of a fort of about 150 ft. in diameter, the rest of the 
fort being of masonry. The battery floor is about 16 ft. above high- 
water, and in all respects the construction of the Portland Fort applies 
to this, except that the armoured wall here consists of only three 
thicknesses of 5-in. plate, which are prepared to receive a fourth when 
necessary. The iron work of this battery was completed in 1875. 
The next works to be described are the two great forts at Spithead, 
standing on either side of the main channel, about 2000 yds. apart. 
(See Diagrams XL and XII.) They are named from the shoals on 
which they stand. 
Their foundations were laid some two or three fathoms below low 
water, and occupy circles of about 230 ft. diameter. The masonry 
work is carried up to a height of about 16 ft. above high water, and at 
that level commences the two-tier circular iron battery for 24 guns 
on the lower floor, and 25 guns on the upper. As hitherto intended 
these were to be all 38-ton (12J-in.) guns below, and 18-ton (10-in.) 
guns above, but it is more than probable that in each tier some of 
these will be superseded by the new type of long, more powerful, and 
more suitable, breech-loading guns. 
The two forts are almost identically the same in dimensions and 
construction. They are circular, to a radius of 100 ft., and the gun 
ports are either 24 or 26 ft. apart. 
Treating each as composed of an inner structure, and an armoured 
wall, as in the other forts, the former—-or skeleton, as we got to call 
it in the course of erection—consists of the following parts- 
First there is a circular base plate 2 ins. thick, and about 3 ft. wide, 
sunk into the masonry, and going completely round the fort. In this 
base are slotted large holes to take the feet of upright armour bars 
which back the armour plates in front of the guns. 
Next come the lower pier casings, 11 ft. 9 ins. and 12 ft. 9 ins. by 
Spitbank 
Fort, 
Horse Sand 
andNoMan’a 
Land Fort. 
