Fort Blockhouse

Not to be confused with West Blockhouse Fort.

Fort Blockhouse
Gosport, England
Fort Blockhouse (centre) and the marina
Fort Blockhouse
Type	Fort, later submarine base
Site information
Condition	Complete
Site history
Built	1431, various additions until 1960s
In use	1431–1539 (as blockhouse) 1539–1956 (as battery) 1905–1998 (as submarine base) 1996–2020 (as training site) 2002- present (as RAMC barracks)
Battles/wars	Siege of Portsmouth (1642)

Fort Blockhouse is a former military establishment in Gosport, Hampshire, England, and the final version of a complicated site. At its greatest extent in the 19th century, the structure was part of a set of fortifications which encircled much of Gosport. It is surrounded on three sides by water and provides the best view of the entrance to Portsmouth Harbour. It is unique in that it was built over five centuries from its original construction as a blockhouse in 1431 to the final addition of submarine base structures in the mid-1960s. Coastal fortification was abolished nationally in 1956, and the fort has not been used in a military capacity since 2021.

The MoD plans to dispose of the site in 2025.

History

View of Fort Blockhouse (bottom left) facing Old Portsmouth across the entrance to the harbour.

Early fortifications (1431–1667)

Following the burning of Portsmouth during the Hundred Years' War, money was set aside in 1417 to provide protection for Portsmouth Harbour. A timber blockhouse was first built on the Gosport side of the harbour in 1431, after authorisation by Henry VI. A chain was strung from Blockhouse point to a similar tower in Portsmouth, which could be raised to prevent entry to the harbour by enemy ships. It was subsequently rebuilt and strengthened, and in 1542 John Leland described it as a round stone tower with ordnance.

Around the year 1539 a 'bulwark' was built by Thomas Spert to the south-west of the blockhouse (where Haslar Hospital now stands); it was subsequently known as Lymden's Bulwark. Further to the south another fort was built in 1545-46 named Haselworth Castle, though this was abandoned only eleven years after construction. The Cowdray engraving of The Encampment of the English forces near Portsmouth in 1545 depicts all three structures, with Haselworth still under construction; two years later the 1547 Inventory of Henry VIII lists 'Lymden's Bulwark by the West Haven, under Captain John Lymden' and also 'Hasillworth Castle', but the blockhouse is omitted (implying it was no longer armed at this time). By the end of the century all these fortifications were in a derelict state, and a few decades later only a mound remained to indicate the site of the former bulwark.

Modernised fort (1667–1877)

Map of Portsmouth c.1668, showing the chain defence across the harbour entrance; Gosport Point, with de Gomme's battery, is to the right.

In 1665, during the Second Dutch War, Sir Bernard de Gomme was commissioned by Charles II to improve the Portsmouth defences. Two years later he installed a new L-shaped battery on Gosport Point (where the blockhouse had formerly stood): it consisted of a row of eighteen guns facing south-east, to protect the seaward approach to the harbour, and two more guns pointing south-west, so as to protect the landward approach to the battery (which was along a narrow spit of land). The following decade an eighteen-gun battery was constructed by de Gomme alongside the Round Tower on the Portsmouth side of the harbour entrance, matching the battery on the Gosport side. To the north, on the west side of the harbour, de Gomme built two square defensive towers, Charles Fort (at Gosport) and James Fort (on Burrow Island), which were completed by 1679; while on the landward side he began constructing a bastioned trace around the town of Gosport in 1678.

Detail of a 1750 map by J. P. Desmaretz, showing Fort Blockhouse (left) in relation to the Round Tower and battery on the other side of the entrance to the harbour.

An inspection in the early 18th century, however, found that the defences had fallen into poor condition; Captain Talbot Edwards (who, as Second Engineer, had been made responsible for surveying the Portsmouth fortifications) said of the battery that 'this work like the rest is all gone to ruine'. Between 1708 and 1714 the battery was completely rebuilt to create a bastioned fort, with a renewed seaward-facing open-air battery to the south-east and significant defensive earthworks to the south-west. The shape of the 18th-century fort can still be discerned and surviving elements of the 1708 works are the oldest still present on the site. The entrance to the fort on the south-west side consisted of a gateway flanked by two demi-bastions; the gatehouse was demolished in the 1960s, but its keystone survives on site, decorated with the arms of the Board of Ordnance and inscribed Anno 1708. The fort was surrounded by a moat on the south-west and south-east sides, the former crossed by a bridge which was protected at its far end by a stone redan and angled outer earthworks. To the north the fort was enclosed by wooden palisades which formed a bastion at the northernmost point. In the 1750s the fort was described as being armed with twenty-one 18 pounder guns and three 6 pounders.

An 18th-century view of Portsmouth from Fort Blockhouse

Beyond Fort Blockhouse the Gosport fortifications were extended northwards in 1757 in order to enclose the Weevil brewery (which had been acquired by the Victualling Commissioners a few years earlier). New defences were constructed for Gosport in 1778, with the bastioned Fort Monckton situated on the ground that had been occupied by Haselworth Castle in the Tudor era. Further renovations took place from 1797 to 1803, amid fears of French invasion. This created a line of bastions defending Gosport all the way from Blockhouse Point up to Forton Lake on the far side of the town, with French prisoners of war making up a part of the construction workforce. These developments rendered some of the older works redundant: both James Fort and Charles Fort were allowed to fall into ruin in the early 19th century.

South Casemates of 1845–48 (being the third reconfiguration of de Gomme's 21-gun battery).

By 1805 Fort Blockhouse was armed with fifteen 36-pounder and fifteen 18-pounder guns. In 1813, as noted on the preserved datestone, the fort began to be remodelled: the west demi-bastion was extended to the north in 1817-20 and not long afterwards the sea battery was rebuilt with thirteen covered casemates housing 32-pounder guns. The upper part of the battery was strengthened and widened in 1845-48, providing space on the terreplein for a further thirteen guns to be mounted en barbette. This work was part of a substantial rebuilding, which saw the creation of the north bastion: a rounded structure built of red brick and fronted in limestone, with upper and lower casemated batteries which provided a field of fire over the harbour. It was linked, to the west bastion on the one hand and to the sea battery on the other, by a pair of long brick-built casemated buildings: the former providing accommodation for officers, the latter for other ranks.

The 18th-century fortifications of Gosport were considered obsolete by the 1859 Royal Commission on the Defence of the United Kingdom. While the commissioners did not recommend any changes to Fort Blockhouse, nor were its armaments updated: in 1867 it was still armed with 32-pounder smooth-bore cannons.

Royal Engineer Submarine Mining Establishment (1873–1907)

Modern buildings can be seen within and beyond the Fort, including the prominent Submarine Escape Training Tower.

In 1873 Fort Blockhouse began to be used by the Royal Engineers as a base for the deployment of remote-controlled submarine mines as a line of defence for the harbour. At the edge of the headland, to the north of the fort, they built a short pier and several buildings over time, including a set of boathouses and cable sheds (which are still in situ as of 2024, alongside an associated slipway). The casemates of the north bastion were converted into stores for mine casings and other new buildings were erected around the site, along with a light rail system to move the mines and explosives. Additional administrative buildings were added in 1884, when the site also became home to the School of Submarine Miners. The pier was extended in 1888, and additional rooms continued to be added for storage and tests until 1891.

In 1892 a new School of Submarine Mining was established on a site at Stokes Bay (close by Fort Gilkicker), which head previously been used for testing and experimental work. That same year the Royal Engineer companies moved from Fort Blockhouse to Fort Monckton; in their place the Portsmouth Militia Division (Submarine Miners) Royal Engineers, previously based at Fort Monckton, moved to Fort Blockhouse, where they remained until 1907. The two forts were linked with a narrow gauge railway, which also extended to the facilities in Stokes Bay; the railway survived into the early 20th century.

Royal Navy Submarine Base (1905-1998)

Main article: HMS Dolphin (shore establishment)

The Royal Navy was not persuaded of the benefits of submarine mining and by 1903 the Admiralty was lobbying the War Office to take over submarine mining bases and replace the fixed minefields with mobile submarines, in order to provide a more effective line of defence. Fort Blockhouse was duly turned over to the Royal Navy in 1905 and, as HMS Dolphin, it became the home of the Royal Navy Submarine Service. The Napoleonic era defences that had extended out to loop around the west side of the town were removed, in order to facilitate transportation. Between the two world wars, the establishment expanded beyond the lines of the original fort on Blockhouse point however, and the prominent submarine escape tower was built in 1953, and opened in 1954. The need for such a training facility had been made apparent by the loss of HMS Truculent in 1950. The battery of the fort was disarmed in 1956, and additional buildings were added to support submarine operations in the mid-1960s. The end of the Cold War brought with it a reduction in defence requirements, with the threat of Soviet submarines having passed- and so in 1992 it was announced that the smaller submarine fleet would be leaving HMS Dolphin and moving west to HMNB Devonport. The last submarine left Dolphin in 1994. HMS Dolphin was declared surplus to requirements in 1996 and Dolphin was formally decommissioned in 1998.

33 Field hospital and Defence Medical Training facilities (1996–2018)

Aerial view of Fort Blockhouse from the north-west (2024).

The Defence Medical Training Organisation (DMTO) was established at Fort Blockhouse in 1996 (close by what was then the tri-service military hospital at Haslar). At the same time, part of the Blockhouse site became the Royal Defence Medical College (RDMC), which provided initial and advanced training for all military Medical Officers and nurses and the majority of medical technicians. Following the decommissioning of HMS Dolphin in 1998, RDMC became responsible for the whole Fort Blockhouse estate. In 2002, however, after Haslar's closure had been announced, the college relocated from Gosport to Birmingham (where the Royal Centre for Defence Medicine had been established the previous year); it now forms part of the University of Birmingham Medical School.

After the closure of the college, the Defence Medical Education and Training Agency (successor to the DMTO) remained, with its headquarters in the Mackenzie Building at Fort Blockhouse; the DMETA maintained a 'small residual training facility' on the site, which was connected with the local Ministry of Defence Hospital Unit. The DMETA was wound up in 2008, and its functions relocated to DMS Whittington as part of Joint Medical Command.

In 1996, 33 Field Hospital relocated to Fort Blockhouse following the closure of Cambridge Military Hospital, Aldershot, where it had been established in 1985. Over the next twenty years the hospital was regularly deployed, to Kosovo, Iraq and Afghanistan, the last deployment being to South Sudan in 2017. 33 Field Hospital was disbanded on 1 December 2018, after 33 years’ existence.

SETT training facility (1998-2020)

The SETT viewed from above (2004).

Although the submarine base was closed in 1998, the Royal Navy Submarine School (RNSMS) remained at the fort until 23 December 1999, and some training continued at Blockhouse for a further twenty years: the submarine school was relocated to HMS Raleigh in Cornwall, with pressurised training remaining at the Blockhouse facility until 2008. The Submarine Escape Training Tank (SETT) remained in service until it was finally closed in January 2020.

Other units

Since 2008 the National Coastwatch Institution has maintained a daily lookout from the fort's signal tower; it was visited by the Princess Royal in 2023.

As of 2022, a number of 'non-military agencies, cadet forces and civilian associations' were based at Force Blockhouse, in addition to the NCI, including: the Royal Naval Sailing Association, Hornet Services Sailing Association, the Royal Navy Submarine Museum and local Sea Cadets and Air Training Corps units.

Saluting station

Up until 2017 Fort Blockhouse was the Royal Navy's main saluting station in Portsmouth. Four QF 3-pounder Hotchkiss guns mounted on the south casemates, the earliest dating from 1886, were regularly used for ceremonial gun salutes (latterly HMS Collingwood provided the gun crews). The use of Fort Blockhouse for gun salutes was of long standing; at the Portsmouth Naval Review of 1773 King George III was greeted by 21-gun salutes from Fort Blockhouse, the saluting platform and Southsea Castle. On an earlier occasion, when Charles II was sailing into Portsmouth to inspect the newly-finished fortifications in 1683, a gunner at Fort Blockhouse was killed when one of the guns burst as the salute was being fired.

Future

Planned disposal

In 2016, it was announced that Fort Blockhouse would be disposed of by the Ministry of Defence in 2020, as part of a wider package of reductions in defence estate. Surveys were undertaken from January to March 2020 to determine which structures at the site would become listed buildings, and major job cuts took place at the end of the year. The disposal date was later extended to at least 2023, and once more to 2025.

External links

• Victorian Forts data sheet
• Fort Blockhouse and Submarine Mining on the Fort Gilkicker website