Former Guardhouse (now called the Post Office), Fort Blockhouse


Heritage Category:
Listed Building
List Entry Number:
Date first listed:
Statutory Address:
Haslar Road, Gosport, Hampshire, PO12 2AB


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Statutory Address:
Haslar Road, Gosport, Hampshire, PO12 2AB

The building or site itself may lie within the boundary of more than one authority.

Gosport (District Authority)
Non Civil Parish
National Grid Reference:


Former guardhouse. Built in the early C19 incorporating the remains of a late C18 forge, converted to a post office and canteen in the C20.

Reasons for Designation

The former guardhouse, built in the early C19 incorporating the remains of a late C18 forge, at the artillery fort known as Fort Blockhouse and converted to a post office and canteen in the C20, is listed at Grade II for the following principal reasons:   Architectural interest:   * as a well-designed and constructed guardhouse, built in the early C19 to form a key part of a bastioned artillery fort;

* for the fundamental survival of the plan which helps to illustrate the guardhouse operation;

* for the vestigial remains of the C18 forge which is thought to have been used for cannon ball manufacture.

Historic interest:   * as an important building in the daily operation of Fort Blockhouse, which was central to the defence of Portsmouth Harbour, subsequently becoming a Royal Engineers establishment for the use of fixed minefields for harbour defence in the late C19, before serving as a principal base and spiritual home of Britain’s submarine service during the C20.   Group value:   * with the scheduled artillery fort, and with other C19 developments such as Arrogant and Thames Block, the former gatehouse datestone and the cannon bollard. The group value extends to listed buildings and structures from other phases including, the Admiralty boundary stone (C18), the Submarine Memorial Chapel (built 1917), the submariners’ memorial (C20), and the Submarine Escape Training Tower (C20).


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 was built on the site. A plan of 1668 shows a fort with defences facing the land and sea. In about 1709, there was major reconstruction work. The fort’s south-west defences were considerably strengthened with a redan, moat and outer work, as well as a south-east sea battery. The remaining north-west and north-east sides of the fort were enclosed by oak palisades with an angled bastion to the north. In the early C19 further work was undertaken, including the northwards extension of the western face of the west demi-bastion and extensive remodelling of the sea battery. Between 1845 and 1848, the sea battery was further strengthened and new casemates were built on the north and the eastern sides of the fort, as well as a limestone-faced north bastion. However, the advent of larger rifled cannon meant the defences became increasingly obsolescent as the C19 wore on.

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. A loading shed, workshops, mess room, boat and cable sheds, and a jetty were built. In 1904, the fort became a submarine base with the addition of new jetties and submariners accommodation. The hulk HMS Dolphin was also brought to the site to provide further accommodation and in 1912 gave its name to the newly established independent command. During the First World War, the base was the Royal Navy’s principal submarine depot and a memorial chapel was erected in 1917. A mock submarine control room known as an ‘Attack Teacher', was also erected along the northern curtain wall; only traces in the brickwork now remain. After the war, the outer C18 defence works were reduced, the moat partly infilled, and several buildings constructed within the fort interior, outside the main gate and surrounding it. In 1935 to 1937, a new headquarters was built for Rear Admiral, Submarines (commander of the service) with an operations room and communications facilities. 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. After the conflict HMS Dolphin resumed its role as the main base for the submarine service, rising in prominence in the mid-1960s when the service provided the country’s nuclear deterrent. The base expanded with many new buildings on the land to the south-west of the peninsula. However, the end of the Cold War in 1991 led to a major reappraisal of defence requirements, and HMS Dolphin closed in 1998. The Submarine School was transferred to HMS Raleigh at Torpoint, Cornwall, and the Defence Medical College was established at Fort Blockhouse; the base being occupied by 33 Field Hospital. In 2016 the government confirmed that Fort Blockhouse was to close; the estimated date for disposal is 2022.

The former guardhouse stands within the courtyard of Fort Blockhouse and historic mapping indicates that there was a building on the site as early as 1750. The rear of the building is thought to have housed a forge for the manufacture of cannon balls by 1798. However, the majority of the present building probably dates from the early C19 and is perhaps contemporary with a remodelling of the main gate around 1813. The roof would have originally been clay-tiled but this has been replaced with slate. A photograph of around 1900 shows that the two windows to the left of the main entrance have been truncated to their existing form and the lintels to the two right hand windows were brick-arched sometime after 1900. The façade originally had two shallow pediments to either end, connected by a parapet wall, which have now been removed above eaves level. The brickwork was also laid in a diaper pattern but the lower portion of the brickwork has been painted dark red on the north-western, north-eastern and south-eastern elevations.

During the 1920s and 1930s development of the fort continued in support of submarine operations and a new guardhouse was built on the approach road. It is probable that the former guardhouse was converted to a post office around this time.


Former guardhouse. Built in the early C19 incorporating the remains of a late C18 forge, converted to a post office and canteen in the C20. MATERIALS: red stock brick and vitrified brick in Flemish bond under a slate roof. PLAN: a single-storey building with a storage attic accessed by taking-in doors in the roof. It is L-shaped in plan, comprising a rectangular main range with the former forge extending from the southern corner. The main entrance is in the centre of the north-west elevation and it opens into a central post room which also has a door to the canteen and strong room. A separate external entrance to the left-hand side of the main entrance opens into the strong room, behind which there is a passageway to the rear yard (door blocked up) and a doorway through to the former cells (originally two, now opened up to one). On the south-west elevation, there are two entrances; one into the canteen and a second into the former forge. At the rear of the former forge there is a back door to the rear yard. EXTERIOR: the principal elevation faces north-west and is formed of seven bays under a hipped roof. The three central bays are set back behind a round-arched, brick colonnade, which carries a post office sign. The central entrance has a four-panelled timber door beneath a transom light of three panes. It is flanked by sash windows of four-over-six panes in plain timber architraves on stone cills. Two further bays stand either side of the colonnade. Those to the right-hand side have a sash window with C20 segmental brick arches and stone cills; one example has four-over-six panes and is set into a timber architrave with a segmental head, the other is a later replacement, which has larger panes in a three-over-four configuration. The original sash windows to the left-hand side of the colonnade have been removed and replaced with high-set, segmentally-headed, hopper windows of six panes, standing on heavy stone cills. A four-panelled timber door stands under the first bay. A rendered plinth runs around the base of the building and the roof ridge has a tall chimney stack to the south-western end. The north-east elevation is largely blind apart from a single, high-set, segmentally-headed metal window of 21 panes. It is located under a brick segmental arch and stands on a heavy stone cill. There are two, rectangular ventilation grates, which have a decorative pattern. The hipped end to the roof has an inset, central chimney stack. The rear (south-east) elevation has evidence of a former doorway now infilled with brick. There are two windows of a similar design to the example on the north-east elevation. One is high-set and has horizontal louvres and the other is low-set and is surmounted by a louvered panel. At the northern end of the wall there is a rectangular, decorative ventilation grate. The south-west elevation is formed of six bays; the first three bays forming the return of the guardhouse and the next three bays formed from the rebuilt former forge to the south-east. The first bay at the north-western end has a timber door with six glazed panes and a blocked transom light above. To the eastern side, there are two sash windows with four-over-four panes. These three bays are unified by matching stone cills and lintels. Above the central bay, there is a lucarne for a sack hoist set into the hipped-roof. It has a hoist beam above a pair of taking-in doors. The next three bays are formed of a later or rebuilt building which holds the remains of the former forge. There is a central, planked entrance door with a three-over-two pane sash window to the left-hand side and a three-over-three example with reconstituted stone lintel to the right-hand side. The rebuilt chimney of the former forge rises through the ridge of the roof where it is attached to another building to the south-east. The north-east elevation of the former forge is similar in form, but most of the lintels have been replaced with reconstituted stone. INTERIOR: the principal rooms have high ceilings and the dividing walls are either of brick or timber-boarded. The timber internal doors mainly consist of four panels and some retain their iron handles and catches. The strong room has a small wall safe (possibly relocated from a submarine or ship), some functional shelving and a blocked-up fire place. The former cells have a bricked-up fire place and functional shelving. One of the two cell doors has been infilled with timber. The canteen area has a blocked-up fire place.

The post room retains its late C20 serving desk*, cupboards and shelves* and the former forge is fitted out with a late-C20 functional kitchen* and canteen room*. These late C20 fixtures and fittings are not of special interest and are excluded from the listing.

The roof structure of the former forge is partially exposed, with visible timber purlins and collars and four squared-timber beams that tie the eastern and western walls together. At the southern end there is a substantial chimney breast which curves to the south-west as it rises to the ceiling. The door through to the former guardhouse has four panels and is set into a simple architrave. Either side, there are two, over-painted, two-over-three pane internal windows.

* Pursuant to s1 (5A) of the Planning (Listed Buildings and Conservation Areas) Act 1990 (‘the Act’) it is declared that these aforementioned features are not of special architectural or historic interest. However, any works to these structures and/or features which have the potential to affect the character of the listed building as a building of special architectural or historic interest may still require Listed Building Consent (LBC) and this is a matter for the Local Planning Authority (LPA) to determine.


Books and journals
Evans, D, Arming the Fleet: The Development of the Royal Ordnance Yards, (1770-1945)
Hall, K, HMS Dolphin: Gosport's Submarine Base, (2001)
Williams, G H, 'The Western Defences of Portsmouth Harbour 1400-1800' in The Portsmouth Papers , , Vol. 30, (1979), .
Francis, P, and Crisp, G, Military Command and Control Organisation, report for English Heritage (2008)
Historic England, Screening for Potential Listing Report: Fort Blockhouse, Gosport, Hampshire (2020)


This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.

End of official listing

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