Admiralty boundary stone, 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:


Boundary stone, erected in 1774 for the Admiralty near the entrance to Fort Blockhouse.

Reasons for Designation

The admiralty boundary stone, erected in 1774 at the entrance to the artillery fort of Fort Blockhouse, is listed at Grade II for the following principal reasons:

Architectural interest:

* as a particularly early surviving example of a military boundary marker that delineated the boundary of the early C18 artillery fort; * as a well-crafted boundary stone marked with the date 1774, the royal cypher of King George III and the fouled anchor of the Admiralty.

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 Grade II-listed cannon, probably of early C19 date, that has been upended to form a bollard close by, and with the scheduled artillery fort, as well as the other Grade II-listed fort buildings, including the former guardhouse, Arrogant Block, Thames Block, the Submarine Memorial Chapel, Submarine Escape Training Tower (SETT), the submariners’ memorial, and the former gatehouse datestone.


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 admiralty boundary stone at Fort Blockhouse was erected in 1774. Military boundary stones served as markers to delineate the boundaries of military sites. Generally, their use appears to extend from the late C18, through the C19 and into the C20, and there are examples that post-date the Second World War. However, most surviving stones will date to the C19 and C20. The boundary stones were typically marked with the broad arrow or crow’s foot of the Board of Ordnance (incorporated into the War Department after 1855) or the fouled anchor motif of the Admiralty. For the latter the direction of the fouling varies and the anchor can be displayed at different angles; vertical, inclined to the left or right, or horizontal. Many boundary stones are marked with the initials of the above departments and may be numbered. The closure of military establishments and new development has often resulted in the loss of boundary stones.

The admiralty boundary stone at Fort Bockhouse is located on the seafront at the neck of the peninsula which leads to the fort. It is situated beyond the location of the redan and outer works which originally stood in front of the entrance and appears to have marked the boundary to the fort. The stone is marked with the royal cypher of King George III and the fouled anchor of the Admiralty. In close proximity to the boundary stone is a cannon, probably of early C19 date, that has been upended to form a bollard.


Boundary stone, erected in 1774 for the Admiralty near the entrance to Fort Blockhouse.

MATERIALS: carved from Portland stone.

DESCRIPTION: the admiralty boundary stone is located next to the sea wall at the neck of the peninsula which leads to Fort Blockhouse. It is situated beyond the location of the redan and outer works which originally stood in front of the entrance. The boundary stone is rectangular in shape with a pointed top. Although heavily weathered, on the front (north-east) face is the faint outline of several incised inscriptions: the royal cypher GR (George Rex) with the date 1774 beneath it and then the Admiralty anchor motif below.


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)
Moore, D, Solent Papers No.13 - Fort Blockhouse and Fort Monckton, (2014)
Williams, G, The Portsmouth Papers No.30: The Western Defences of Portsmouth Harbour 1400-1800, (1979)
Historic Gosport: Military Boundary Stones, accessed 6 April 2020 from
Information on military boundary stones, accessed 6 April 2020 from
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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