Former Gatehouse Datestone, Fort Blockhouse


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


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Statutory Address:
Fort Blockhouse, Haslar Road, Gosport, 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:


Gatehouse datestone, originally built as part of the gatehouse to Fort Blockhouse in about 1709. Altered with an additional inscription in around 1813. Moved and placed on a concrete plinth as a freestanding monument following the demolition of the gatehouse in 1960.

Reasons for Designation

The gatehouse datestone, originally built as part of Fort Blockhouse in about 1709, altered with an additional inscription in around 1813 and relocated on a concrete plinth as a freestanding monument following the demolition of the gatehouse in 1960, is listed at Grade II for the following principal reasons:

Architectural interest:

*     as a substantial architectural component from the C18 fort gatehouse, complete with Queen Anne cypher and regimental inscriptions, relocated to the adjacent grass bank as a free-standing monument.

Historic interest:

*     for its historic association with Fort Blockhouse, a bastioned artillery fort that was central to the defence of Portsmouth Harbour in the C18 and C19, subsequently becoming a Royal Engineers establishment 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, adjacent submariners’ memorial, the former guardhouse, Arrogant Block, Thames Block, the Submarine Memorial Chapel, the boundary stone and a cannon bollard along with Submarine Escape Training Tower, all of which are listed at Grade II. 


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 gatehouse datestone is located next to the entrance and curtain wall on the south-west side of Fort Blockhouse, alongside other commemorative structures including a submariners' memorial. The gatehouse was originally erected in about 1709 when a redan, moat and outerwork were built on this side of the fort. In about 1813 the fort was strengthened, including work to the west demi-bastion. The datestone carries the dates 1709 and 1813 in respect of these events. It is also marked with the royal cypher and crown of Queen Anne. In about the 1920s the moat on this side of the fort was infilled and in 1960 the gatehouse was demolished to ease the movement of motor vehicles. The datestone was retained and subsequently moved to this position adjacent to the fort entrance.


Gatehouse datestone, originally built as part of the gatehouse to Fort Blockhouse in about 1709. Altered with an additional inscription in around 1813. Moved and placed on a concrete plinth as a freestanding monument following the demolition of the gatehouse in 1960.

MATERIALS: Portland stone ashlar on a concrete plinth.

DESCRIPTION: datestone to the former gatehouse at the entrance to Fort Blockhouse, now a freestanding monument. It is around 4m high and 2m wide and rests on a two-tiered stepped concrete plinth. The lower part of the datestone comprises the tooled Portland stone voussoirs which originally formed the entrance arch to the gatehouse. The keystone is carved with a shield bearing three cannons set on wheeled gun carriages beneath three cannon balls. Above the shield is the inscription ANNO and beneath it the date 1709, each set within a cartouche. The next stage is formed by a stone course and then a frieze surmounted by a cyma-reversa moulding. The frieze carries the inscription: REFORMED/ MDCCCXIII. Surmounting the frieze is a stone panel carved with the royal cypher and crown of Queen Anne flanked by two shoulder-scrolls; one enriched with rose decoration and the other a thistle. It is topped by a cornice with a cavetto and cyma-recta moulding. The back and side of the monument are plain, having been made-good with render.


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. Number 30, (1979), Unknown
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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