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Fortifications of the Isle of Wight - Horse Sand Fort

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Fortifications of the Isle of Wight

West Wight Fortifications
Freshwater Redoubt | The Needles Old Battery | New Needles Battery | Hatherwood Battery | Warden Point Battery
Fort Albert | Cliff End Battery | Fort Victoria | Golden Hill Fort | Bouldnor Battery
East Wight Fortifications
Puckpool Battery | Nodes Point Battery | Steynewood Battery | Culver Battery | Bembridge Fort
Redcliff Battery | Yaverland Battery | Sandown Granite Fort | Sandown Barrack Battery
Solent Sea Forts
St Helen's Fort | No Man's Land Fort | Horse Sand Fort | Spitbank Fort

Horse Sand Fort was one of the two largest Solent sea forts, and was built to be virtually identical to its twin, No Man's Land Fort. It was one of the first sea forts proposed, and the Royal Commission on the Defences of the United Kingdom approved construction in 1860. Work began on constructing Horse Sand Fort in July 1861 but work was suspended between 1862-1865 due to political indecision. The fort was finally finished in 1880.

Horse Sand Fort's Position

Horse Sand Fort was built on Horse Sand Shoal and guarded the mainland side of the deep-water channel that large vessels such as warships would use to enter the Solent to reach Southampton Water and Portsmouth Harbour. The Isle of Wight side was guarded by No Man's Land Fort, 2,139 yards south-east of Horse Sand Fort. The forts were positioned so that any enemy vessels wishing to attack the Royal Navy's Naval Base at Portsmouth would be forced to sail between, and be bombarded by, the heavily armed forts. As the front line of defence for Portsmouth from any sea attack, Horse Sand Fort was heavily armed and heavily armoured, equipped to stop an enemy fleet if necessary from attacking the Royal Navy, Britain's first line of defence against invasion.

The original design was for 27 guns on the lower gun floor, 28 guns on the upper with up to 12 guns in turrets on the roof, a total of up to 67. Horse Sand Fort would also be the control station for the network of submarine mines in the Spithead entrance.

Submarine Mines

The submarine mines laid between the forts were known as electro-contact mines. A mine was moored to float beneath the water's surface, and if a ship struck the mine, the mine would send an alarm to the submarine mine control station at Horse Sand Fort. Here the operator could fire or prevent the explosion of the mines depending on whether the vessel was friend or foe. The electro-contact mines were considered to be a reliable weapon that could be used no matter the weather, even on foggy nights when observation of enemy ships through dense fog patches could render searchlights useless.


Horse Sand Fort was built with two gun floors and a basement. The whole of the fort's circumference at gun-floor level was armoured with iron, supported by iron framework. The armour is 25-inches thick, made of five alternating layers of 5-inch thick wrought iron and iron concrete plates. The fort had originally been designed to be built entirely of granite, but in the 1860s the power of guns had increased so much that only iron armour would be able to withstand bombardment.

At the seabed the fort's walls are 59 feet thick and its diameter is 240 feet. The fort's base is 210 feet in diameter with the fort narrowing to 204 feet 9 inches above1. The foundations on the seabed were built with rings of prepared Roach Portland stone on the outside – 8-ton concrete blocks were laid in a ring and filled in the centre with shingle from the sea bed. The floors and roof were made of bomb-proof concrete and the fort was designed to be able to mount further guns in turrets on the roof. Brick piers direct from the seabed foundations were constructed to take the weight of five turrets so the fort's superstructure would not be affected.


The basement level was used primarily as the fort's magazine and stored the shells and cartridges for the guns. Four circular passageways circumnavigated the fort, with the pump for the well and the spiral staircase in the centre. Part of the central passage was the lamp lobby and off the central passage were the kitchen, provision store, penstock chamber where waste could be flushed away from the fort, ablution room and the laundry and drying rooms. The middle passage was accessed by a separate spiral staircase and accessed fourteen cartridge stores, cartridge lifts to the floors and the general stores lift on the north side, as well as access to the light passage's stairs. The light passage provided protected light to the cartridge and shell stores below.

24 shell stores and lifts opened off the outer passage, as well as a chamber that allowed access to the narrowest passage next to the outer shell of the fort, the bolt passage. This was designed to allow extra iron armour to be bolted onto the outside of the fort should weapon design improved, making the fort's armour insufficient. The chamber also provided access to the electric cables that controlled the minefield placed between Horse Sand and No Man's Land forts.

The basement level was later modified in 1882. The bolt passage was filled with sand and the outer shell stores filled with concrete to provide the magazine with extra protection and to cope with the increased gun weight above. Steam boilers, an accumulator and a hydraulic pump were also installed in the centre.

Lower Gun Floor

The lower gun floor had gun positions around the outside for 24 heavy guns, with ammunition hoists and lifts nearby to deliver the shells and cartridges from the basement. The gun emplacements were originally intended to house 10-inch guns; however when the fort was armed it was instead fitted initially with 12.5-inch 38-ton RMLs and later the more powerful 12-inch breech-loading guns.

On the north of the floor was the entrance to the fort via a staircase from the two-floor landing stage. As well as the outer door, a thick armoured door protected entry into the fort and led to a corridor leading to the outer passage. This armoured door was made of iron and was designed to be re-enforced by a 34-ton sand-filled armoured box that ran on rails and could be wheeled into place to effectively seal the only entrance.

Between the outer passage and the gun emplacements to the north were the latrine and the NCO's quarters. In the centre of the fort off the Central Passage, which was accessed by a corridor on the North side, were five officer's quarters, the officer's mess, the officer's kitchen, the officer's servant's quarters and the officer's latrine. Also from the central passage were the stairs to the upper floor, with stairs to the basement off the corridor leading north.

Between the outer gun casemates and the central core was a fourteen feet wide, open circular passage, known as 'The Street', around the central building.

Upper Gun Floor

The outside ring of the upper gun floor had positions for 25 guns. One gun position was above the casemates on the lower gun floor, with an additional one above the entrance. It was on this floor that seventy-two soldiers lived in peacetime, in five rooms behind the gun emplacements that each housed 18 men. These rooms were separated from the gun casemates by shutters on rollers only, allowing the rooms to be opened in the event of attack. On the north side were stairs leading to the lower floor as well as a trapdoor to allow guns to be lowered to the floor below.

In the central core building on this level were the lighthouse keeper's quarters and officer's servant's quarters, as well as the water cisterns.


Although the fort had been designed to have five turrets each armed with two guns, these were never built in order to save money. The roof originally was constructed with only a lighthouse on top, as well as ventilation vents and chimneys. At the end of the century position-finding cells had been emplaced, although these were removed in 1909. The roof was later adapted to hold three 6-inch breech-loading quick firing guns and the required expense magazine. New position-finding equipment in a building on the central core that was later extended to house the Battery Commander's Post, a fire control position and a Naval Signal Station, which required a flag mast, yard and flag locker. This was one of the major differences with No Man's Land Fort, which was not used as a Naval Signal Station. Both forts housed searchlights on the roof, for aircraft as well as ship spotting duties, and during the Second World Horse Sand Fort was armed with an anti-aircraft gun.


After the political indecision that delayed construction for much of the 1860s, Horse Sand's Fort's design was finally approved by the Defence Committee on 28 April, 1866. Seventy workers and a steam-powered crane worked to construct the fort, which eventually cost £424,000 rather than the estimated £260,000. The forts were constructed out of stone and concrete blocks that were checked to ensure they would fit, taken to the site of construction by barge and then lowered into position by crane under the direction of divers on the seabed. This work was contracted out to Mr Leather, who was also responsible for building the Plymouth Breakwater Fort.

As weapons designs kept improving while the forts were being constructed, one of the principle difficulties was keeping the forts compatible with the most modern weapons available. The earliest proposals had included plans for a battery of mortars2 on the roof. Mortars were considered to be obsolete by the time the fort was completed in 1880.

In 1871 it was envisioned Horse Sand Fort had would house 15 12-inch 35-ton RML guns and 34 10-inch 18-ton guns. The 35-ton guns would provide greater armour penetration at long range than the 18-ton guns and would be positioned to face the main approach to the fort.

By 1874, however, this plan had changed. Instead the fort would carry 24 12.5-inch 38-ton RMLs on the lower gun floor, 25 10-inch 18-ton RMLs on the upper gun floor with an additional 10 12-inch 35-ton RML guns on the roof in five turrets. This would make it impossible for any enemy vessel under any circumstances to enter Spithead without having been subject to heavy fire. After the forts were constructed, the delay and the higher than expected costs meant that the turrets were never built for financial reasons.

The 12.5-inch RMLs would have needed 20 men to man each gun, plus seven more for ammunition duties. To fully man each of the fort's 49 guns 1,300 men would have been required, so it is unlikely that it was intended for the forts to need every gun fully manned. Horse Sand Fort only routinely provided accommodation for 200, although hammock hooks were installed so additional men could be housed if necessary.

Armament of the 1880s

In July 1880 the Inspector General of Fortifications reported that Horse Sand Fort was completed and a satisfactory work.

When the 12.5-inch guns were fitted by the end of 1880 it was found that the casemates were too cramped for the guns to be able to use a full charge of powder. It had been necessary for the guns to be fitted on short 6-foot recoil platforms rather than the 7-foot the guns had been designed for in order to fit in the casemates. This was unable to cope with the gun's full recoil with a full charge of powder. Consequently this affected the guns' performance and ability to penetrate the armour of attacking warships.

An alternative was quickly sought and in 1882 new 12-inch 43-ton breech-loading guns were available, and were fitted in alternate casemates on the lower gun floor's seaward side, the side most likely to face an attack. As the weight for each gun was increased the outer magazines in the basement below were filled in with concrete to help support this weight, and the bolt passage was filled with sand. This also gave the fort added protection from incoming fire. In order to deal with the dreaded problem of recoil the guns were mounted in special 'yoke' mountings. This was two vertical iron beams that attached from floor to ceiling either side of the gun, spreading the shock of recoil to both the floor and the roof. This took up even more space in the casemates and affected the ability of the gun to traverse.

The fort retained the 10 12.5-inch 38-ton RMLs on each gun floor in a secondary role. 15 machine guns were added as part of the fort's small arms.

The basement level was later modified in 1882. The bolt passage was filled with sand and the outer shell stores filled with concrete to provide the magazine with extra protection and to cope with the increased gun weight above. Steam boilers, an accumulator and a hydraulic pump were also installed in the centre.

In 1883 it was also decided that it was unnecessary to mount heavy guns on the fort's north-west side, as large enemy vessels would only be able to get to that position after passing the minefield between the two forts. Only weapons suitable for attacking light draught vessels especially light, fast craft armed with torpedoes were required. Reducing the armament of the fort allowed some vacant casemates to be filled with concrete whilst in others could be mounted quick firing guns. In 1884 Horse Sand Fort was armed with ten 12-inch 47-ton breech-loading guns, seven 12.5-inch 35-ton RMLs, eight 10-inch 18-ton RMLs and 24 6-pounder Nordenfelt quick firing guns. These quick firing guns were mounted on special casemate saddle mountings in some emplacements to allow the gun to fire through the embrasure and be swung inside the fort, out of the way, when not in use.3

The 12-inch guns were found to be too big to manoeuvre effectively by hand and were slow to traverse, and so hydraulic machinery was requested to assist in the traversing and elevating of the guns. Colonel Maguire-Bate, Inspector of Iron Structures, supervised the installation of the hydraulic machinery and the associated boiler, pumps and accumulator and introduced a revolutionary hydraulic system in 1884. This not only traversed and elevated the guns but was also extended to open and close the breech and load and ram home the shells and charges, as well as raise the cartridges and shells from the magazines and move the armoured door. There were some teething difficulties with this revolutionary system: in a trial one of the guns was fired at too high an angle, causing internal damage to the fort.

When the position-finding cells were placed on the roof, the guns could be controlled from there. Horse Sand and No Man's Land were the first forts in Europe thus capable of having their guns controlled and powered from a central point. Electric lights were also introduced at this time.

There were even plans to emplace even larger 12.1-inch 50-ton breech-loading guns, but as the casemates were too small to fit these, this proposal was quickly abandoned. There was a plan to construct a new sea fort tower 400 yards east of Horse Sand Fort to fit these guns, and even plans to construct turrets armed with 17-inch 100-ton guns, but these were abandoned due to the phenomenal costs involved.

In 1886 the Stanhope Committee on the Sea Defences of Portsmouth reported that the Horse Sand and No Man's Land Sea Forts were:

'So essential to the security of the [Portsmouth] dockyard that it is of primary importance that they should be armed with heavy guns and their magazines made secure'.

1890 to 1914

In 1898 the Montgommery Committee on the substitution of breech loading and quick firing guns for existing RML guns recommended that:

'At... Horse Sand Fort the RML guns should be reduced with the exception of two 12.5-inch in each fort, the left hand pair, which should be retained as fixed point guns. Three 6-inch QF should be added to each fort in sponsons with arrangements to give them a wide arc of fire over interior waters.'

The 10-inch RMLs were removed to be sold as scrap in 1904. The only use the 12.5-inch RMLs had were two 'running past' guns. In 1902 three embrasures were modified to allow for an added traverse of 88 degrees and had 6-inch mark VII breech-loaders installed. Two were fitted on experimental electrical mountings, but the test was not a success and the electric mountings were replaced with standard centre pivot mountings in 1908. The 6-inch Mark VII gun was the standard coast-artillery weapon of the early 20th Century, designed by Vickers Son & Maxim4 and could fire a 100 pound shell through 15 inches of armoured plate at 1,000 yards, making it particularly effective against unarmoured ships. Three more were installed on the roof in 1912.

In 1905 the Owen Committee on the Armament of Home Ports report declared that the 12-inch guns were redundant. The 9.2-inch guns on the Isle of Wight and on the Mainland were able to repel large warships, with the sea forts' role changing to stop smaller vessels entering Spithead and Portsmouth Harbour. To aid with this a line of concrete blocks was sunk in 1909 from Horse Sand Fort to Southsea Beach, near Southsea Castle, to prevent an enemy from sinking a blockship across Portsmouth Harbour and preventing the Royal Navy from leaving port. The Owen Committee however stated that the three six-inch guns were:

'Sufficient as anti-torpedo-craft guns on his line... The 12-pdr and 6-pdr QF and the 12.5-inch RML on Horse Sand Fort should be removed.'

Electric lights were installed on the fort at this time, but all but two of the 12.5-inch guns were removed and sold as scrap iron.

In 1906 Major-General Chas Cecil Dalton, Inspector Royal Garrison Artillery, inspected Horse Sand Fort and reported:

'I prefer to have the two 9.2-inch guns removed from Puckpool and placed on top of Horse Sand Fort where they would get extensive range to seaward and all round.'

However, this proposal was not acted upon.

In 1907 six additional 6-pounder quick firing guns from No Man's Land Fort were installed in Horse Sand Fort. By 1909 the fort was armed with thirty 6-pounder quick firing guns and nine 12-inch guns, which had only 50 rounds each, and two 12.5-inch RMLs had only case shot for use against light craft. These older guns were intended only as 'fixed point' or 'running past' guns, to be fired when an enemy vessel reached a fixed point in the gun's sights, and so the hydraulic machinery was removed in 1907.

In 1908 the 6-pounders were removed from Horse Sand Fort and in 1912 Horse Sand Fort was armed with three 6-inch breech-loading guns on the roof, which stayed until 1950. Horse Sand Fort still had nine 12-inch breech-loading guns in reserve and the two 12.5-inch RMLs, although the ammunition for these weapons would not be replaced.

The World Wars

During the Great War the English Channel was considered comparatively safe from surface vessel attacks compared to the vulnerable North Sea. The straights of Dover were heavily patrolled and mined, preventing any enemy surface vessels from approaching the English Channel. Although Horse Sand Fort was fully manned, it played no role in the conflict.

The gun floors were modified to provide officers and soldiers quarters for the men manning the roof's guns, and dining rooms, washroom, generator room, a NAAFI canteen and even a small theatre. Life on the forts during the war was monotonous. Although in fair weather a steam vessel delivering supplies and stores would call twice a day, in rough weather the forts had to survive on emergency rations. Searchlights were installed in the fort and Royal Navy vessels leaving or entering Portsmouth Harbour had to sail in accordance with carefully prepared plans so that they would not be illuminated by the searchlights and give their positions away to enemy observers. An anti-submarine boom was constructed and positioned off from Horse Sand Fort.

In 1916 one 6-inch gun was removed from Horse Sand Fort and sent to the vulnerable East Coast of Scotland to aid in the defence there. As the English Channel remained safe it was decided in 1916 to save fuel by only exposing the searchlights when an alarm sounded.

In 1919 the troops were withdrawn from Horse Sand Fort, with only a caretaking team remaining. In 1921 the fort was placed in care and maintenance. In 1925 all the 12-inch guns and both 12.5-inch guns were removed and sold for scrap, leaving only two 6-inch guns and a 3-inch anti-aircraft gun. This was removed in 1941 and fitted to a merchant vessel, as there was a severe shortage of anti-aircraft guns in the Battle of Britain and the early part of the Second World War. A boom defence had been laid between the two main Solent forts and an indicator loop was placed on the seabed to detect enemy vessels.

Post War

In 1951 the 6-inch guns were removed and in 1957, after Coast Defence had ended, the searchlights were removed and sold off. Horse Sand Fort was scheduled as an Ancient Monument in 1967. Although the fort was unarmed and deactivated it was retained by the Ministry of Defence until 1993 when it was sold to the Portsmouth Naval Base Property Trust for £80,000. Although they had initially promised to restore the fort and open it to the public, they placed it in on the market in 2002, when it was bought by Optima Cambridge Property Development to be converted into luxury apartments, although this project seems to have stalled.

1Both measurements include the outer walls.2Mortars were short gun designed to fire shells high in the air and then send them vertically down, often used to attack ships. They were inaccurate weapons, especially at long range, but for the short range between the two forts a large number of mortars had the potential to cause a lot of damage to the decks of enemy ships, traditionally the least armoured parts of a warship.3The British Nordenfelt quick firing gun was similar to, but not as successful as the French Hotchkiss 6-inch quick firing gun. In 1888 the Nordenfelt Guns and Ammunition Company was taken over by the Maxim Gun Company to form The Maxim Nordenfelt Guns and Ammunition Company.4Vickers was an engineering company founded in 1828. In 1897 they took over The Maxim Nordenfelt Guns and Ammunition Company, becoming Vickers, Sons & Maxim. They later in 1927 merged with Armstrong Whitworth, the company behind the Armstrong breech-loading gun to become, Vickers-Armstrong Ltd and in 1928 purchased Supermarine aircraft, famous for the Schneider Cup aircraft and the Spitfire. Vickers was nationalised in 1960 to become British Aerospace and is now part of BAE Systems.

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