Summary
The upstanding remains, earthworks and buried remains of an early C18 bastioned artillery fort.
Reasons for Designation
Fort Blockhouse, a bastioned artillery fort built in the early C18 to defend the entrance to Portsmouth Harbour, is scheduled for the following principal reasons:
* Rarity: as a relatively rare example in England of a true bastioned artillery fort;
* Historic interest: as the site of an early C15 blockhouse defending the entrance to Portsmouth Harbour, an additional bulwark in 1538, refortified with a gun battery following the Second Dutch War (1672-1678) in the late C17, before a bastioned artillery fort was constructed in the early C18. Fort Blockhouse was an important Royal Engineers establishment for mining purposes in the late C19 before it became one of the Royal Navy’s principal submarine bases in the C20;
* Architectural interest: as a well-constructed early C18 artillery fort with bastions, curtain walls and casemates erected in high quality tooled ashlar masonry;
* Survival: most of the enceinte and curtain walls survive, as well as bastions, dry ditches, a former guardhouse, casemates including gun emplacements and magazines, officers’ quarters and other accommodation;
* Documentation: the site is well documented in historical terms, including written accounts, historic plans, maps and photographs;
* Potential: for archaeological deposits associated with the construction and use of the fort, which with the built fabric will significantly enhance our understanding of C18 bastioned forts. In addition, buried remains or artefactual evidence relating to the early C15 blockhouse, Lymden’s Bulwark of 1538, and the late C17 artillery fort may also survive;
* Group value: with the designated artillery fortifications associated with Portsmouth Harbour, such as the Round Tower, Fort Monckton, Fort Gilkicker, Fort Grange, Fort Cumberland, Southsea Castle, Portsmouth town defences and Eastney Fort, among many others; together serving as an impressive ensemble that well illustrates the defence of this strategic harbour over a long period of time.
History
Fort Blockhouse is sited on the western side of the entrance to Portsmouth Harbour at the end of a peninsula joined to Haslar by a narrow neck of land. A timber blockhouse was recorded on the site in the early C15. It stood opposite The Round Tower (NHLE 1386901) on the eastern side of the harbour entrance; a chain between the two securing the entrance against enemy ships. In about 1538, the west side was refortified with the addition of Lymden’s Bulwark but by the late C16 the fortifications were derelict. In the late C17, during the Second Dutch War (1672-1678), concerns over the vulnerability of naval dockyards to attack led to new schemes by the great fortress engineer Sir Bernard de Gomme to strengthen Portsmouth’s defences. An L-shaped battery with at least 14 guns was built on the site. Drawings indicate the parapet was of stone with a rear masonry terreplein on which the guns were mounted. At the centre was a small single-storey building, apparently timber-framed with brick infill and a tiled roof. A plan of 1668 shows a fort with defences facing the land and sea and capable of mounting 21 guns.
In about 1709, there was major reconstruction work. The fort’s south-west defences were considerably strengthened by the addition of an angled earthwork outer work with a track through them leading to an angled inner defensive wall, or redan, probably in stone. This in turn protected a bridge that gave access over a moat to the main gatehouse between the originally symmetrical west and south demi-bastions. The south-east side of the fort, Sea Battery, was formed by embrasures that held thirteen 32 pounder guns. Unusually, the remaining north-west and north-east sides of the fort were enclosed by oak palisades with an angled bastion to the north; strong enough to resist an initial attack, but if Blockhouse was overrun its interior would still remain vulnerable to guns on the Portsmouth side. A moat extended in front of the Sea Battery on the south-east side of the fort and around the demi-bastions to the south-west. At the north-west end of the moat a wall projecting westwards from the west demi-bastion closed the end of the moat and within it a sluice controlled the level of water within the moat. This wall extended westwards to protect the northern side of the outworks. The moat remained open to at least 1925 but by about 1931 it had been infilled and built over. In the 1750s, it was reported that Fort Blockhouse mounted twenty-one 18 pounder guns and three 6 pounders.
In the early C19, further work was initially prompted by the French Revolutionary Wars. This included the northwards extension of the west face of the west demi-bastion with a return to the east finally completed between 1817 and 1820. The Sea Battery was also extensively remodelled. Within the courtyard a building is shown on the site of the former guardhouse (now called the Post Office) from the 1750s, although the present building may date to around 1813 when the gate was being remodelled. Also in the courtyard were the Master Gunner’s House and a magazine capable of holding 100 barrels of powder (both since demolished).
Between 1845 and 1848, Fort Blockhouse underwent further alteration. The Sea Battery was strengthened by thickening its stone parapet and the terreplein was widened. This allowed 13 extra gun positions to be placed on an upper deck providing a total of 26 guns. The casemates were probably closed by brick walls at this date and by the end of the century they were used mainly as stores. The north-west and north-east sides of the fort were also considerably strengthened. To the north the timber bastion was replaced by the limestone-faced North Bastion with upper and lower batteries, originally designed to house smoothbore muzzle-loading cannon. Along the north-west side new quarters were provided for officers in eight bombproof brick casemates, now incorporated into Thames Block. These quarters were glazed on the courtyard side and entered up steps through a single door protected by a wooden porch. At the centre of the range a passageway gave access to the exterior. The quarters were defensible with a raised loop-holed parapet commanding the courtyard with presumably a similar outward-looking arrangement. A staircase at the west end gave access to the walkway of the north loop-holed curtain wall that joined to the west demi-bastion. To the rear of this wall were the officers’ water closets. Bombproof accommodation with loop-holed parapets was also provided for soldiers along the north-east wall, now incorporated into Arrogant Block. Originally, the north-east elevation was blank with lower narrow horizontal embrasures and an upper loop-holed parapet, both probably for musketry. Later, windows were inserted into this elevation.
By 1864, the western landward approaches to the fort were covered by nine guns. Also by this date the east demi-bastion had been constructed at the entrance to the harbour. However, the advent of larger rifled cannon greatly increased the ranges at which engagements might take place and the defences at Fort Blockhouse became increasingly obsolescent. In 1885, the fort was armed with ten 64 pounder rifle muzzle-loaders and two smoothbore guns. By 1888, these had been reduced to three 64 pounders and three machine guns to protect the inner minefield. In the late C19, a new threat emerged from small, fast motor torpedo boats and to counter this menace five 12 pounder quick-firing guns were installed at Fort Blockhouse.
In 1873, Fort Blockhouse was taken over by the Royal Engineers who were engaged in the use of fixed minefields as a means of harbour defence. The casemates of the North Bastion were used for storing new mine casings. In the courtyard a loading shed and mess room were built. North of the North Bastion workshops, boat and cable sheds and a jetty on Haslar Creek were built. Subsequently the regular mining engineers moved to Fort Monckton and the Southern Submarine Mining Militia occupied Blockhouse. By 1905, a large loaded mine store had been added at the centre of the courtyard.
In 1900, the Royal Navy ordered its first submarines, initially for harbour defence. In late 1904, anticipating the obsolescence of defensive mining, the First Sea Lord Admiral Fisher started making arrangements for the submariners to move into Fort Blockhouse. Haslar Creek was dredged and two new jetties were constructed for the submarines in about 1909. To accommodate the submariners, the officers’ quarters in Thames Block were extended and in 1913 Hazard Block was added for the more senior officers. It was probably at this time that a pedestrian access was also made through the north curtain wall. The hulk HMS Dolphin was also brought to the site to provide additional accommodation and on 31 August 1912 gave its name to the newly-established independent command.
During the First World War, HMS Dolphin was the Royal Navy’s principal submarine depot. In 1917, a small memorial chapel was built on top of the North Bastion. A mock submarine control room, known as the Attack Teacher, was also built along the north wall of the west demi-bastion and north curtain wall at around this time. It was designed to train submariners in the use of the periscope, utilising a horizontal opening in one of the elevations linked to scale targets sighted along the adjacent curtain wall. This was incorporated into Dolphin House in the 1930s and it was possibly at this date that the three 12 pane sash windows were inserted in its north wall. It is believed that Dolphin House was used to brief submarine captains before missions. A new Attack Teacher was subsequently installed in a purpose-built building elsewhere on the base.
A number of other works were also carried out to Fort Blockhouse following the First World War; the outer C18 defence works were reduced, the moat partly infilled, and several buildings constructed immediately to the west of the fort. On the approach road a new guardroom was added, Mercury Block constructed and the Bonaventure Block built on the site of the Master Gunner’s House. Thames Block was progressively extended to create an Officers’ Mess. In around 1928, several buildings were added within the fort courtyard or parade ground: No.1 Sub-station; Rapid Block; Chief Engine Room Artificers Bath House and Locker Flat; Ships Company Washing and Drying Room; the Fort Offices; a large canteen (demolished); Pactolus Block; and the Bath House and Stores. Outside of the north-east defences, overlooking the harbour entrance, an accommodation block for warrant officers, Maidstone Block (now called Clyde Block), was constructed. It was linked to Thames Block by a first floor bridge giving access to a covered way around the upper level of North Bastion. To the north, further officers’ quarters; Forth Block, were soon added. In 1931 a Seamen’s Block, Vulcan, was built outside the main gate. Overlooking the main jetty and Haslar Lake a headquarters building was built for Rear Admiral Submarines with an operations room and communications facilities in 1935 to 1937.
At the outbreak of the Second World War, HMS Dolphin was home to 5th Submarine Flotilla. Operations were conducted in the Channel and the Bay of Biscay, and in June 1944 X-craft from HMS Dolphin were used to mark the D-Day landing beaches. Due to its vulnerable position at the head of Portsmouth Harbour, most submarine training was transferred elsewhere and the Admiral’s headquarters moved. Mine-watchers’ posts were built on the west and east demi-bastions. An additional storey was added to the latter in the late 1950s and it is now occupied by the National Coastwatch Institution.
After the war, HMS Dolphin resumed its role as the main base for the submarine service preparing boats for operational service, maintenance work and crew training. In 1960, the original gatehouse to the fort was demolished to ease vehicular access. The submarine service rose in significance in the mid-1960s when it took over responsibility for providing the country’s nuclear deterrent. This expansion was reflected in further new buildings at the base outside the boundary of the original artillery fort, particularly to the south-west of the peninsula.
The end of the Cold War led to a major reappraisal of defence requirements, and subsequently the formal closure of HMS Dolphin on 30 September 1998 and transfer of the Submarine School to HMS Raleigh at Torpoint, Cornwall, on 23 December 1999. The Defence Medical College was established on the site and the base occupied by 33 Field Hospital, in addition to providing accommodation to smaller units and personnel in the Portsmouth area. In 2016, the government confirmed that Fort Blockhouse was to close; the estimated date for disposal is 2022.
Details
The standing remains, earthworks and buried remains of an early C18 bastioned artillery fort.
PRINCIPAL FEATURES
Fort Blockhouse is situated on a shingle peninsula on the western side of the entrance to Portsmouth Harbour. A blockhouse stood on the site in the early 1400s and in 1538 Lymden’s Bulwark was added. In the late C17 a gun battery was built before being reconstructed in the early C18 as a bastioned artillery fort with further alterations in the C19. Buried remains of the earlier fortifications may survive on the site. The ramparts and fort curtain wall that now form the main enclosure or enceinte of the bastioned artillery fort are built to a broadly square plan, orientated north-east to south-west, with a bastion at the north angle, large demi-bastions at the south and west flanking the main entrance, and a small demi-bastion at the east. At the south-east is a seaward-facing casemated battery. Further casemated accommodation blocks were later added at the north-east and north-west (now Thames Block and Arrogant Block) but these buildings are Grade II-listed and excluded from the scheduling although the ground beneath them is included. There is an extant dry ditch or moat flanking the North Bastion (partly-infilled) and fronting the Sea Battery but on the south-west side of the fort it now survives entirely as a buried feature. An angled outerwork with a track leading to an angled inner defensive wall, or redan, was also built in front of the entrance in the early C18 but has largely been levelled although there is likely to be surviving buried archaeological remains.
DESCRIPTION
The main approach to the fort is at the south-west where the peninsula is attached to Haslar by a narrow neck of land. It was protected by an angled outerwork with a track leading to an angled inner defensive wall, or redan, in the early C18. This was largely levelled in about the 1920s but part of the earthworks of the outerworks are defined in later hardstanding next to the sea wall (at SZ 62509 99144) and there is likely to be further buried archaeological remains. The track led to a bridge across a moat on the south-west side of the fort; this was infilled between 1925 and 1930 but the stone-lined moat, together with a sluice and remains of the bridge, will survive as buried remains. The early C18 ashlar masonry wall that extended from the west demi-bastion to enclose the north-west side of the moat and protect the northern side of the outerworks survives and is visible beneath the north side of Pandora Block (Building 43 on the MOD site layout plan (dated 18 July 2007)) and to the north of the Latrine Block (40). The gatehouse on the south-west side of the fort was demolished in 1960 with only the datestone retained as a freestanding monument nearby, which, alongside the mid-C20 submariners’ memorial stone next to it, is Grade II-listed and excluded from the scheduling although the ground beneath it is included. The early C18 curtain wall on this side of the fort is formed of finely-tooled ashlar blocks topped by a cordon; above this the parapet has been replaced and the wall heightened in red brick at a later date with stone quoins and a red brick or stone coping. Next to the sea wall are the remains of a Second World War gun emplacement for two 6 pounder guns added in about 1940 (at SZ 62558 99161).
The early C18 WEST DEMI-BASTION has an earth backing forming a terreplein approached by earth ramps from the courtyard or parade ground. Built into the terreplein are two brick barrel-vaulted expense magazines with segmental-headed openings flanked by buttresses. The west face of the west demi-bastion was extended to the north with a return to the east in 1817 to 1820. The west face is built in the same style as the earlier wall but the east return is of red brick except for a lower ramped section in stone at the north angle. The east return has low square loopholes, now blocked, at the east end. On the inside of the wall is a parapet walk supported by a brick round-arched blind arcade. There are narrow loopholes to the parapet and a metal railing to the parapet walk. A large vehicle entrance was inserted into the east end of this wall, replacing a smaller pedestrian entrance close to where it adjoins Thames Block (88), in about 1960 and some of the brickwork was renewed at this date.
A mock submarine control room, known as an Attack Teacher, was built along the north wall of the west demi-bastion and north curtain wall during the First World War. Trace evidence of the structure is apparent from the light orange brickwork to the curtain wall. It was incorporated into DOLPHIN HOUSE (92), which was built onto the west wall of the demi-bastion in the 1930s and is considered to have functioned as a briefing house for submarine captains before missions. It is a two-storey red brick building, nine bays long and two bays wide, with a hipped slate-covered roof; however at the north it reduces to a single-storey and there is an adjoining single-storey extension with three sash windows in the position of the former Attack Teacher. The windows to the main range are metal casements and top-hung windows divided into subsidiary lights to the ground floor, although several bays are blind (without openings) and the fourth bay of the west elevation has an oriel window. The building was heightened in about the late 1980s when the upper storey was added in dark red brick with PVC windows matching the glazing pattern of those below. There are two partially-glazed wooden doorways with transom lights in the east elevation. Internally, there is a mess room, kitchen and bathroom to the ground floor and bedrooms and a bathroom to the first floor; all largely with late 1980s or later fixtures and fittings which are excluded from the scheduling.
Immediately to the south of Dolphin House is a square, concrete, brick-faced MINE-WATCHERS’ POST built on top of the curtain wall. This was added during the Second World War and served as a post to spot and plot the position of parachute mines. The structure has two large openings faced in concrete overlooking the jetties and Haslar Lake. It is accessed from the rear by a steel ladder through a pair of outward opening steel doors. Internally, there are sliding steel shutters with a wooden shelf beneath. Outside of the former main gate and next to the west demi-bastion are low concrete walls with wooden covers, which may mark the entrances to Second World War air raid shelters.
The early C18 SOUTH DEMI-BASTION has a curtain wall of finely-tooled ashlar blocks topped by a cordon and red brick parapet. The interior of the bastion was hollowed out and largely levelled in around 1918 when several buildings were inserted into this space, including the accommodation and stores block Pactolus.
At the south-east of the fort is the SEA BATTERY (55), originally constructed in the early C18 and fronted by a stone-lined moat, but extensively remodelled in the early C19 with 13 covered casemates. It is constructed of finely-tooled ashlar and has round-arched openings with large stone voussoirs facing the sea beneath a cordon and stone parapet. The moat in front of the battery is about 115m long by 8m wide and enclosed by stone walls built into or abutting the sea wall. The part of the sea wall contiguous with the moat and east demi-bastion dates from about the early C18 and is included in the scheduling. In 1845 to 1848, the Sea Battery was strengthened; the stone parapet thickened and the terreplein widened by 5ft (1.52m) to provide 13 extra gun positions on an upper deck with the guns firing en barbette, directly over the parapet. The rear extension is carried on brick arches supported by projecting angle piers that also mark the position of the expense magazines; a total of 13 separate magazines where powder charges and filled shells were originally stored. The barrel-vaulted casemates and magazines were subsequently closed by brick walls. Most of the casemates now have a central door with a transom light flanked by sash windows with a continuous stone lintel. The window sills incorporate a stone ‘wedge’ to either side (also seen on Arrogant Block) possibly associated with armoured shutters. Most of the doorways to the casemates and magazines now (2020) contain C20 flush timber doors but there are also original armoured metal doors with strap hinges, one of which is marked as ‘No1 Gunners’ Store’. The casemates are currently used as stores but in a number of them pivots survive beneath the embrasures on which cannon carriages were mounted. They also incorporate several probably later C19 personal equipment racks and hooks (probably for hammocks). The gun embrasures are now sealed by casement windows. The upper deck of the Sea Battery is approached by steps at the east and west end. The deck retains the gun positions, holding down rings and pivots on which the carriages were mounted. Later additions include two raised concrete emplacements for 1890s 12 pounder quick-firing guns with built in cartridge stores but now featuring four 3 pounder Hotchkiss saluting guns. At the west end of the upper deck is another former quick-firing gun position that was given a brick and concrete cover for a Bofors 40mm gun during the Second World War. Nearby is a stone setting for a wireless mast added in about 1915. At the east end of the upper deck is a single-storey brick store with a sash window, C20 timber-boarded door, flat felt-covered roof, and two adjoining cartridge stores.
The EAST DEMI-BASTION (56) adjoining the Sea Battery is constructed of red brick and has a parapet walk supported by a blind round-arched arcade. There are loopholes to the brick parapet, an iron railing to the parapet walk and pedestrian openings inserted in the north and south-east walls. In addition there is an earlier phase (or phases) of stone masonry at the foot of the bastion. At the angle of the bastion is a former flank tower, probably added in the mid-C19 but used as a signal station by 1938 before being converted into a mine watcher’s post during the Second World War. An additional storey was added in the late 1950s when it became a Sea Safety and Hailing Signal Station. It was refitted in 2001 as Port Entry Control on behalf of HM Queen’s Harbourmaster and since 2008 it has been occupied by the National Coastwatch Institution. The modern fixtures and fittings, communications and surveillance equipment and antennae are excluded from the scheduling. In front of the former flank tower is a low concrete emplacement with built in cartridge stores for a 1890s 12 pounder quick-firing gun set within a brick and ashlar wall (the gun is no longer in place).
The north-west and north-east sides of the artillery fort were originally enclosed by stout oak palisades with an angled bastion to the north but these defences were replaced in 1845 to 1848. Officers’ quarters were provided in eight bombproof brick casemates on the north-west side of the fort, now incorporated into Thames Block (88) which is Grade II-listed and excluded from the scheduling, although the ground beneath it is included. Similar bombproof accommodation with loop-holed parapets was provided for soldiers on the north-east side of the fort and is now incorporated into Arrogant Block (57) which is Grade II-listed and excluded from the scheduling, although the ground beneath it is included. Arrogant Block is attached to the North Bastion via a red brick curtain wall with a parapet walk.
The NORTH BASTION (83) was built in 1845 to 1848 and is of similar construction to the Sea Battery. It is built of finely-tooled limestone ashlar forming a rounded bastion adjoined to the fort by two straight walls incorporating upper and lower casemated batteries. This was originally designed to house smoothbore muzzle-loading cannon, although in 1865 it was modified to accommodate rifled muzzle-loading artillery. The lower battery has round-headed openings beneath a cordon and stone parapet into which are cut the embrasures of the upper battery. The bases of the two straight walls were protected by stone-lined dry moats. The one to the west remains open and is about 21m long by 5m wide but the other moat was probably filled during the interwar period and now survives as a buried feature. The barrel-vaulted casemates and interior wall of the bastion are built of red brick with a stone staircase providing access to the upper deck from the south. The casemates were used for storing new mine casings after the base became a Royal Engineers submarine mining establishment in 1873. Mines were moved on an 18-inch gauge railway and between 1885 and 1890 an opening was cut through the North Bastion to link the fort’s courtyard with the jetty area. The upper deck of the bastion includes a raised concrete gun emplacement for a 1890s 12-pounder quick-firing gun (the gun is no longer in place) and its associated cartridge stores, as well as two former machine gun positions. A large bollard used for hauling in and out the harbour defence boom was later inserted into the quick-firing gun position. A small memorial chapel (84) was built on top of the North Bastion in 1917; this is currently (2020) in ecclesiastical use and is Grade II-listed and excluded from the scheduling. Clyde Block (formerly Maidstone Block (85)) was built to the east during the 1930s and is linked to Thames Block by a bridge and covered way around the upper level of the North Bastion. Clyde Block is excluded from the scheduling but the ground beneath part of it, which includes the in-filled moat of the North Bastion, is included. The casemates of the North Bastion are currently used as stores and closed off by partially-glazed timber panels with timber doors. However, a number of them retain gun races and pivots on which cannon carriages were mounted.
EXTENT OF SCHEDULING
The scheduled area includes the main enceinte of the bastioned artillery fort demarcated by the fort ramparts and curtain walls, the North Bastion, demi-bastions at the south, west and east, the Sea Battery, and the ground beneath the former casemated accommodation blocks. It also includes the moats (buried or otherwise) flanking the North Bastion and in front of the Sea Battery, as well as the part of the sea wall contiguous with the latter and with the east demi-bastion. In addition, it includes the area covered by the former moat, outwork and redan with associated earthworks, upstanding and below-ground remains at the south-west of the fort. See the Description above for more detail.
EXCLUSIONS
The admiralty boundary stone (at SZ 62497 99116) and the former guardhouse (now called the Post Office (50)), as well as the gatehouse datestone (at SZ 62541 99252), the mid-C20 submariners’ memorial stone, Arrogant Block (54), memorial chapel (84) and Thames Block (88), are Grade II-listed and therefore excluded from the scheduling but the ground beneath them is included. The following buildings are also excluded from the scheduling but the ground beneath them is included: Mercury Block (45), St Ambrose Church (46), Onyx Block (47), Pactolus accommodation and stores block (49), Automat (51), No 1 Sub Station (58), Rapid Block (60), Alecto Block (61), Bonaventure Block (89), Hazard Block (90), Officers’ Mess (unnumbered, NGR: SZ 62628 99326) within the fort, as well as the store buildings next to the squash court (31, 34), the squash court itself (32), the sick bay block (33), ASA Centre (37), Sewage Pumping Chamber (38), Latrine Block (40), Vulcan Block (41), Fire House (42), Pandora Block (43), ASA Store (44), and No 3 Substation (102) near the entrance to the artillery fort. Clyde Block (63) is excluded from the scheduling but the ground beneath part of it, which includes the buried moat of the North Bastion, is included.
The late C20 or later internal fixtures and fittings to Dolphin House are excluded from the scheduling. The modern internal fixtures and fittings, communications and surveillance equipment and antennae of the National Coastwatch Institution Signal Tower, are also excluded from the scheduling.
In addition to any exclusions detailed above, the monument also excludes: the paved, tarmacadam or concrete surfaces of all modern roadways, pathways or car parks; all modern signs and sign posts, lamps and lamp posts; security cameras; drains and drain covers, cycle racks, bins, electricity junction boxes and cables, flags and flag poles, loud speakers, benches, modern bollards, modern fences and fence posts, later C20 and C21 railings. However, the ground beneath all these features is included.
