Slough Fort and wing batteries
Heritage Category: Scheduled Monument
List Entry Number: 1021405
Date first listed: 12-Nov-2009
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The building or site itself may lie within the boundary of more than one authority.
District: Medway (Unitary Authority)
National Grid Reference: TQ 83764 78492
Legacy Record - This information may be included in the List Entry Details.
Reasons for Designation
The Royal Commission fortifications are a group of related sites established
in response to the 1859 Royal Commission report on the defence of the United
Kingdom. This had been set up following an invasion scare caused by the
strengthening of the French Navy.
These fortifications represented the largest maritime defence programme since
the initiative of Henry VIII in 1539-40. The programme built upon the
defensive works already begun at Plymouth and elsewhere and recommended the
improvement of existing fortifications as well as the construction of new
There were eventually some 70 forts and batteries in England which were due
wholly or in part to the Royal Commission. These constitute a well defined
group with common design characteristics, armament and defensive provisions.
Whether reused or not during the 20th century, they are the most visible core
of Britain's coastal defence systems and are known colloquially as
`Palmerston's follies'. All examples are considered of national importance.
Slough Fort is an essential component of the Royal Commission fortifications for north Kent, linking the Thames Estuary and Medway forts and protecting part of the Hoo peninsula. The monument survives in good condition and its significance is enhanced by the 1889-91 addition of two wing batteries for 'disappearing' guns. These gun emplacements are an unusual and nationally rare survival because of the very short time span in which their technology was deployed (less than twenty years). The monument is a physical manifestation of the very rapid changes in artillery and naval technologies in the late-C19 and early C20. SOURCES: Gulvin KR, Medway Forts, pp16-17 (2000) Saunders, A & Smith, V, Kent's Defence Heritage, Kent CC & English Heritage (2001) Palmerston Forts Society website: http://palmerstonforts.org.uk (accessed 2009)
Legacy Record - This information may be included in the List Entry Details.
The monument comprises parts of Slough Fort and its wing batteries. The core
of the fort is protected by its listed building status and is therefore not
included in the scheduling but is briefly described below to allow an
understanding of the historical development of the site in its entirety.
HISTORY: Slough was constructed in 1867, as a direct consequence of the 1859
Royal Commission on the Defences of the United Kingdom, to link the Medway
defences, including Grain Fort, with other new forts in the Thames Estuary
such as those at Cliffe and Shornemead on the north Kent coast. It was an
integral part of a defensive system comprising a ring of coastal
fortifications on both sides of the Thames that provided artillery fire
against hostile shipping in the estuary. Slough Fort also provided protection
at a local level against enemy landings on the neighbouring beaches as well
as the approach to Yantlet Creek to its east. The fort was subsequently
modified in the late-C19 and early-C20, most significantly by the addition of
a wing battery to both the east and west of the original fort core and a
quick-firing battery on the fort roof. The fort continued to be used during
World War I and was finally abandoned by the army and then sold in the 1920s.
In 1861, a year after the Royal Commission Report, land to the value of
£1,639 was purchased to enable the construction of Slough Fort. It was
completed by 1867 and provided a casemated battery housing seven 7 inch
Armstrong rifled breech-loading guns, manned by a garrison of three officers,
one NCO and 75 other ranks. In 1885 the Secretary of State described the work
here as unfinished, but this probably only referred to the lack of gun
shields for the embrasures (the opening through which a gun fires) of the
casemates (or gun chambers) as these were never installed.
Major redevelopment took place at Slough between October 1889 and December
1891 when two wing batteries were constructed. Each wing battery had two
breech-loading 'pop-up' or 'disappearing' guns of a 6 inch and 9.2 inch
calibre. Positioned in deep concrete emplacements these were on
hydro-pneumatic mountings made by the Elswick Ordnance Company.
Hydro-pneumatic power enabled the gun to 'pop up' over the top of the
emplacement for firing and the recoil caused it to retract or 'disappear'
into the safety of the emplacement for reloading hence the alternative names
for this type of gun and gun mounting. An underground magazine was also
located between each pair of emplacements. As a consequence of this
redevelopment the seven casemates in the main body of the fort became
obsolete. At this time the front (north) of the fort was enclosed by a
substantial earth bank, rising almost to roof level. This covered the former
casemate embrasures and offered protection against incoming enemy fire. The
guns were removed and the casemates were converted into permanent barrack
accommodation: three became married quarters, one was converted to officers'
quarters and accommodation in the remaining three casemates housed 17 men.
New detached quarters for a Warrant Officer, a small detachment of Royal
Engineers and barrack stores were also constructed to the south-east of the
fort. The fort roof space was modified to accommodate a depression
range-finding instrument which calculated the distance and bearing of a
target and relayed this information to the guns. The defensive ditch across
the gorge (rear) to the south of the original fort is also believed to have
been back-filled at this time with new and more extensive defences being
constructed to protect the rear of the fort and the wing batteries. Provision
was also made for the storage of moveable guns and their ammunition which
would have been employed in the vicinity of the fort when needed. These
comprised four 16-pounder rifled muzzle-loaders, three 3-pounder quick-firing
guns and six 0.45 inch machine guns.
It is clear that at some point light quick-firing guns were mounted on the
roof of the fort as there is physical evidence for at least two emplacements
with ready-use ammunition lockers and structures to the rear that may have
been gun-floor shelters for the crews. These are clearly later than 1892 as
detailed plans of that date do not show these features. One 3-pounder
quick-firing gun was certainly in place by 1898 and two more followed by
1900. They were very short-lived as they had been removed by 1903. It is
possible the quick-firing guns recorded as both moveable and fixed armaments
are one and the same and were moved dependent upon need. Whereas the 6 inch
and 9.2 inch guns in the wing batteries served against larger warships, these
quick-firing guns were designed to counter the threat from fast and light
vessels such as torpedo boats.
Armaments tables and other contemporary reports provide useful information
regarding the armaments at Slough between 1898 and World War One. It is clear
that by the late 1890s, in common with all coast artillery batteries,
recommendations had been made to convert the disappearing guns to fixed
mountings. These employed a much simpler principle whereby the barrel
recoiled along its axis, enabling a much quicker rate of fire. By 1906 two
new 9.2 inch fixed guns had been installed in the eastern wing battery while
one 9.2 inch and one 6 inch pop-up gun remained in place in the western wing.
By 1907 the latter two had been removed.
Slough Fort continued to play a key strategic role and was manned during
World War I. A Battery Command post appears to have been added to the fort
roof at this time, possibly occupying the site of one of the quick-firing gun
emplacements. This provided facilities for observation, command and control
of the guns as well as telephone communications. A Thames Port War Signal
Station was also located to the east of the fort in the early-C20 (in a
surviving building known locally as the Coastguard Cottage). This was
operated by the coastguard to communicate with all shipping entering and
leaving the Thames. Through liaison with the Slough Fort battery commander,
the Port War Signal Station ensured that no hostile shipping could pass the
The army abandoned the fort in 1920, finally selling it in 1929 when it was
used to house a small zoo. There is currently no evidence to suggest that
Slough was re-requisitioned and re-armed during World War II although beach
defences were erected to the north. In the post-war period the fort belonged
to the Allhallows Estate Company and then Strood Rural District Council. The
latter intended demolition but the costs were prohibitive. Planning
permission for conversion to riding stables was therefore granted in the
DESCRIPTION: Slough Fort is a D-shaped, two-storey casemated work of Kentish
ragstone and brick with high quality granite dressings. It is probably one of
the smallest of the 70 or so forts built as a result of the Royal Commission.
As originally conceived the ground floor comprised seven granite-faced gun
casemates in a curved battery to the north and defensible barracks to the
south enclosing a small parade ground. The roof level, accessed by two
enclosed spiral staircases, provided an observation post with banquette (an
infantry firing step for close defence from ground assault).
The fort was entered from the south, protected by a now in-filled ditch
crossed by a drawbridge. Evidence for this survives in the form of drawbridge
pulleys either side of the original metal-plated gates. Infantry rifle
loopholes on either side of the entrance protected the landward approach.
The eastern wing battery contains two gun emplacements for Nos. 1 and 2 guns
and their underground magazine. Gun Emplacement No. 1 was the most easterly
of the four emplacements on the wing batteries (The east-west numbering
employed follows that on contemporary military plans). It is roughly
semi-circular in shape and originally a concrete emplacement for a 6 inch
breech-loading gun on a hydro-pneumatic mounting. First constructed in
1889-91 it was modified in 1906 to accommodate a 9.2 inch breech-loading gun
on a fixed 'barbette' mounting. (The barbette is a reinforced parapet over
which a gun fires). This gun required a shallower emplacement, a problem
solved by the insertion of a raised steel gantry in an arc around the rear of
the emplacement to form a walkway and loading platform for the gun crew. This
was supported on vertical steel columns and anchored into the barbette by
horizontal girders. Although the gantry has been removed, four roughly-cut
parallel grooves on each side survive to demonstrate the girder positions.
No. 1 emplacement is largely in-filled with horse manure (2009) which
presumably preserves the gun floor and magazine relatively intact. The gun
floor would have had a holdfast plate (for securing the gun mountings to the
floor), ready-use ammunition lockers and a dials recess for the receipt of
information from the range-finders. Several steel ring-bolts are visible,
however, which would have secured the ropes and lifting equipment (in the
form of temporary A-frames) for manoeuvring guns and heavy equipment.
The large semi-circular concrete 'apron' on the seaward side of the
emplacement is intact. This would have served to protect the gun and deflect
incoming fire. An earthwork defence to protect the back of the gun would be
expected to the east and south of No. 1 and this is shown on a plan of 1892.
However, the level of infill is now (2009) such that this element is not
currently visible. The emplacement appears to have gone out of use and the
gun was removed in 1918.
A subterranean magazine with a number of internal chambers lay between No. 1
and No. 2 emplacements, beneath the straight wall joining the two. This was
shared by both guns although the two gun crews would have worked
independently. Inside were stores for cartridges, shells and side arms.
Ammunition would have been raised to the guns by mechanical lifts (comprising
a steel tray and chain), the vertical shafts for which are visible in each
barbette. Concrete steps rise onto the 'apron' between the two emplacements.
Gun Emplacement No. 2 lies to the immediate east of the main fort and is
connected to it by a flanking wall. This is a further concrete emplacement
but this time for a 9.2 inch breech-loading gun on a hydro-pneumatic
mounting. Built in 1889-91 it was modified in 1906 for a 9.2 inch gun on a
barbette or fixed mounting. No. 2 emplacement is also largely in-filled with
horse manure (2009) which conceals much of the emplacement. However,
ring-bolts of the same form and function as for No. 1 emplacement and
modifications for the fixed gun are visible. This emplacement also appears to
have gone out of use at the end of World War I.
The western wing battery also contains two gun emplacements for Nos. 3 and 4
guns as well as their underground magazine. Gun Emplacement No. 3 lies to the
immediate west of the main fort and is connected to it by a flanking wall
(part of which is visible). This is an emplacement for a 9.2 inch
breech-loading gun on a hydro-pneumatic mounting, built in 1889-91. Of
concrete construction, it survives in very good condition and is of
particular interest as it was not subsequently modified. It is roughly
semi-circular in shape with an indented flanking wall extending to the east
from the south-east corner of the gun pit. All of the original rectangular
recesses in the barbette are visible, although all have lost their original
locker doors. The six largest comprise three pairs of ready-ammunition
lockers. The western and central pair are each served by a small recess
above, presumably for storing fuses for the shells and tubes for igniting the
cartridges. A smaller cupboard on the east flank would have housed the dials
linked to the range finders. Iron lamp brackets also survive as do the
ring-bolts noted in the east wing battery. The concrete gun floor is visible
and the position of the gun racer (the curved iron track which enable the gun
to move in an arc to its target) can be seen. The height from the gun floor
to the top of the parapet is approximately 4.5m.
The apron and glacis (the external slope of a defensive work carefully
profiled to absorb and deflect incoming fire and to provide a clear field of
fire against attack) for No. 3 lie to the north, beyond a fence which
separates the riding school from the holiday park. However, the fall of the
land here indicates that these features survive buried and intact. A
subterranean magazine of the same form as in the east wing battery would have
existed to serve this and the adjacent No. 4 gun. It is likely that this also
survives in situ to the west of the emplacement. To the south of No. 3 the
ground has been remodelled to form a ménage for the schooling of horses. The
emplacement appears to have gone out of use and the gun removed in 1907.
Gun Emplacement No. 4, also built in 1889-91, lay to the west of No. 3 in an
area now used by Allhallows Holiday Park. It was originally the most westerly
emplacement and was designed to house a 6 inch breech-loading gun on a
hydro-pneumatic mounting. No. 4 emplacement appears to have gone out of use
and the gun removed in 1907. Although no longer visible the topography would
suggest that it survives as a back-filled feature. Aerial photographic
evidence indicates that this infill occurred sometime between 1966 and 1973.
No. 4 is of particular interest as it is the only surviving unmodified 6 inch
hydro-pneumatic emplacement on the site.
To the west of the stables (to the south-west of the main fort) lies an
early-C20 building with a date stone of 1902. This is a single-storey brick
and concrete rectangular structure with a flat concrete roof and four windows
(which are a later insertion). It probably served as a gun detachment shelter
for the men in the wing batteries. Annotations on a plan of 1892 indicate
that this location had been approved for the construction of a casemated
To the east of the stables (to the south-east of the main fort) is a concrete
U-shaped protecting wall for the fort well. This is shown on a plan of 1892
as operated by a windmill pump with water piped into the main fort.
EXCLUSIONS: All modern (post-1945) buildings and structures, modern ground
surfaces, telegraph poles, fences and signs are excluded from the scheduling,
although the ground beneath them is included. All existing services and their
trenches are excluded from the scheduling although the ground around and
beneath them is included. The central D-shaped core of the fort comprising a
foundation, ground and roof level is not included in the scheduling and
instead is listed at Grade II*. However, for the avoidance of confusion, the
earth rampart to the north of the fort and flanking walls to either side are
included in the scheduling.
MAP EXTRACT The site of the monument is shown on the attached map extract.
The contents of this record have been generated from a legacy data system.
Legacy System number: 36202
Legacy System: RSM
Books and journals
Gulvin, K, Medway Forts, (2000), 16-17
Saunders, A, Smith, V, Kent's Defence Heritage, (2001)
http://www.palmerstonforts.org.uk, accessed from
CAB18/19, CAB 16/1, Armament Returns 1898-9, 1900, 1902, 1904-10,
Film 82/713, frame V 0024, 6 Feb 1953, MOD, (1953)
Film OS/66133, frame 030, 4 Jun 1966, Ordnance Survey, (1966)
Film OS/78123, frame 017, 17 Aug 1978, Ordnance Survey, (1978)
Film OS/93340, frame 21, 20 June 1993, Ordnance Survey, (1993)
Title: Plan of Slough Fort Source Date: 1897 Author: Publisher: Surveyor: 160/97, 16 Jun 1897
Title: Plan of Slough Fort Source Date: 1919 Author: Publisher: Surveyor: WO/78/4431, 1919
TQ87NW14 - KE3201, SMR, SMR Record,
TQ87NW14, unique identifier 418721, NMR, NMR record,
WO32/6358, WO33/311, WO33/395, Various records 1898-9, 1904, 1906,
WO78/4531. 24 Aug 1892, Plans and elevations of Slough Fort, (1892)
This monument is scheduled under the Ancient Monuments and Archaeological Areas Act 1979 as amended as it appears to the Secretary of State to be of national importance. This entry is a copy, the original is held by the Department for Digital, Culture, Media and Sport.
End of official listing