The Solent Sea Forts are four forts built to defend the area of the eastern Solent known as Spithead, an anchorage south of the Spit Sand shoal outside Portsmouth Harbour. Spithead was used as an area where ships could safely anchor, protected from the winds, between Portsmouth and the Isle of Wight. Although the eastern entrance to the Solent appears wide, there are in fact hazards to shipping just below the water level in the form of sandbanks and shoals. Ships, such as warships, entering the Solent and approaching Portsmouth Harbour have to keep to narrow deep-water channels between these sandbanks. In the 1860s it was decided that the best way to defend Portsmouth Harbour, home of the Royal Navy, from a French attack would be to build sea forts on some of these sandbanks and shoals.

In 1858 William Armstrong produced a rifled breech-loading gun that significantly increased the range and penetrative power of heavy guns, although frequent use reduced the power, range and accuracy of these weapons. While Britain had a monopoly on these weapons, it was assumed that France would soon catch up with weapon design – this would equate to a French fleet being able to anchor at Spithead and bombard Portsmouth while outside of the range of existing British fortifications. Portsmouth was defended from the sea by Fort Cumberland (which only effectively protected Langstone Harbour¹), Southsea Castle, Point Battery, Fort Blockhouse and on the west side Fort Monckton and Fort Gilkicker. These forts were considered to be insufficient to guard Portsmouth harbour, the most important military site in Britain throughout the Victorian era.

Why It's The Fort That Counts

There were various proposals made other than the construction of sea forts for the defence of the Solent. However, the Crimean War (1854-6) had focused attention on sea forts and sea defences like never before². The Russian naval base in the Baltic at Kronstadt³ was protected by sea forts and a sea barrier, and was considered the strongest fortress in the world and impenetrable. As a consequence it had not been attacked by the allied French and British forces during the Crimean War, and was considered a model for the Portsmouth defences. Although a barrier such as at Krondstadt across the Solent was dismissed on the grounds of the cost of construction and for fear that it would result in the silting up of the deep water channels, sea forts were theoretically cheaper and a stronger deterrent.

The other main option discussed was the construction of floating batteries. These were essentially armoured warships designed not for manoeuvrability or seamanship but instead to float in a fixed location. They would be heavily armoured and mount heavy weapons, and would be cheaper to construct than sea forts. Indeed, proposals were to convert old obsolete warships into floating batteries simply through adding armour plates to their sides. During the Crimean War the French had used floating ironclad batteries to great effect at the Bombardment of Kilburn in October 1855, where they destroyed the Russian forts protecting the Dnieper river. Floating batteries proved an evolutionary dead-end and were replaced by mastless turret-ships, such as HMS Devastation, in the 1870s.

In the end the construction of sea forts was considered the best option. Although more expensive than floating batteries, sea forts would be a permanent defence rather than the temporary measure. A fort would not need to take into account the thickness of its armour and the weight and recoil of its guns in order to maintain its position. For a floating battery to be a real threat to an enemy armoured ironclad fleet it would need to be protected by the thickest armour available and carry the heaviest guns⁴, which would have the most powerful recoil. All of this would seriously affect the stability of the battery, if not its ability to remain afloat, especially as it would be required to stay in the Solent in all weather.

The official Naval position at the time was that it was considered unwise to fetter any ships or crews to harbour defence and thereby reduce our offensive power at sea, and that the range and power of guns would increase and consequently the area guarded by the forts would increase.

Forts are also more accurate than ships and floating batteries. Each gun mounted in a fort was considered to be equivalent to three in a ship. A fort provides the defender with a stable firing platform and the advantage of being able to pre-sight their weapons to where a ship would approach. The roll and yaw of the sea, even in calm waters, affects floating batteries' and ships' guns, greatly reducing accuracy. Forts would also be less cramped than their floating counterparts. These arguments were persuasive enough to result in the building of the Solent sea forts, despite immense opposition.

Two Committees, A Royal Commission and Parliament

In 1857 a committee was set up to investigate 'the probable influence of the new rifled cannon on existing fortifications and future plans for new works of defence'. It concluded in 1859 that the eastern Solent required batteries to be built on the shoals between the Isle of Wight and Hayling Island, supplemented with floating defences at either end. The Royal Commission on the Defences of the United Kingdom took these findings, called several experts including four admirals, four naval captains, three artillery officers, two engineers, Sir James Scarlett⁵, and Sir William Armstrong. When the Royal Commission made its report in February 1860 it agreed with the Committee on the Probable Influence of Rifled Cannon and went into more details. It concluded there were five objects to consider in defending Portsmouth.

• The protection of the harbour entrance.
• The prevention of an enemy from landing between Browndown and Fort Cumberland, the area either side of Portsmouth.
• The protection of the Spithead anchorage, and of the dockyard against bombardment from there.
• The defence of the Needles Passage. The West Wight forts addressed this.
• The prevention of a hostile landing on the Isle of Wight. Principally the Sandown Bay forts addressed this.

The Royal Commission agreed with the existing proposals that identical forts should be built on the shoals at No Mans Land and Horse Sand, where the main channel into Portsmouth and the Solent narrowed to just over 2,000 feet. They also recommended that supporting forts should also be built on Spit Sand (just outside Portsmouth Harbour) and the Sturbridge Shoal (a shoal located halfway between the Isle of Wight and Gosport), as well as a fifth fort located halfway between Horse Sand and Portsea Island⁶. They also wished for two supporting batteries to be built on the Isle of Wight to help support these forts⁷ as well as moveable floating batteries to help give support wherever and whenever needed.

The Royal Commission's findings were put before a Defence Committee. This consisted of eight military officers, two of whom had been in the Royal Commission. Of the others, one was Vice Admiral Sir Richard Dundas, the First Sea Lord, who had commanded the allied fleet in the Baltic during the Crimean War, and the Duke of Cambridge, who was Commander-In-Chief of the Army and Queen Victoria's cousin. The Defence Committee approved all these proposals, calling the arguments for them 'convincing and conclusive'. The next stage was getting Parliamentary approval.

As soon as the proposals reached Parliament there was an outcry about the expense involved, especially from Mr Gladstone who wished to reduce the budget and abolish income tax. The Solent Sea Forts were one of the most controversial parts of the entire Royal Commission's proposals, with only the forts proposed for Portsdown Hill encountering more opposition. To save money, the Spitbank Fort and the fort proposed between Horse Sand and Portsea Island were dropped from the proposals.

By this time it was 1861, three years after the proposals were first made. Admiral Sir Richard Dundas had a slight change of heart and wished that ironclad floating batteries should be substituted for the Spitbank Fort and perhaps elsewhere, at least until the forts were completed.

Cowper Coles' Opposition

A more prolonged opponent of the forts was Captain Cowper Coles. He was the son of a Hampshire parson and had joined the Royal Navy when only eleven. In the Crimean War he had fought with distinction during an abortive naval attack on Sebastopol's sea defences⁸. He then designed an armoured gun-raft that he intended to use in the Crimean War to attack Kronstadt, bypassing the existing defences by navigating the shallow waters undefended by the sea forts; however the war ended before this vessel was completed. Since the Crimean War he had designed and called for the introduction of low draught armoured vessels carrying one gun in a revolving turret based on this idea. He was convinced that only these vessels could defend a harbour effectively, which he stated in a pamphlet written on the Defence of Spithead.

His other arguments were that gunnery tests carried out at Shoeburyness⁹ showed that ironclads were impervious to current weapons at ranges of over 1,000 yards and the Spithead forts were positioned just over 2,000 yards apart, which would allow ships to pass between them without coming into range. Furthermore, as gunners in a fort would, after a few shots, would be blinded by the guns' smoke, the forts would then be firing blind. An enemy fleet could easily manoeuvre between the forts and position themselves where they could attack Portsmouth dockyards from up to 7,000 yards away.

As a result of this in 1861 the Defences Commission was recalled to consider Admiral Dundas' suggestion, Cowper Coles' pamphlet and the gunnery tests being carried out at Shoeburyness. The Defence Commission deliberated and then came to the same conclusion as before. Their reply to Coles' conclusion that ships could pass between the sea forts and shell Portsmouth with impunity was that 'even if the enemy fleet reached such positions, they would be obliged by the tide to anchor if they were to have any hope of maintaining an accurate bombardment, and would then be exposed to a concentrated fire from forts and batteries, while the defending ships would seize the opportunity of attacking any weak spot in their formation.'

In 1862 opposition to the sea forts grew with the events of the American Civil War. On 9 March, 1862 at Hampton Roads the Confederate super-weapon, the ironclad Merrimac, was fought to a standstill by the turret-ship Monitor. The Monitor was designed by the Swedish engineer Ericsson and resembled the low-draught armoured turret-ship that Coles had been proposing. Coles accused Ericsson of stealing his idea, however there is no evidence of this and it is likely that Ericsson came to the same conclusions for an effective warship design independently, although his turret design was less effective. Subsequent warships of this design were known as Monitors. Coles used the interest in the Monitor v Merrimac battle as an opportunity to launch a publicity campaign calling to replace all existing naval vessels with ships to his design. As a result of this the House of Commons passed a resolution that it was 'expedient to suspend the construction of the proposed forts at Spithead until the value of iron-roofed gunboats for the defence of our ports and roadsteads shall have been fully considered.'

The Defences Committee was again convened and asked whether it wished to reconsider its recommendation of constructing forts in the Solent. When Captain Coles was brought forward as a witness to give his report, he ignored all questions put to him and instead distributed copies of his pamphlets and praised his turret-ship designs. The Defence Committee, encouraged also by the Shoeburyness armour plating gunnery trials, stuck to its guns, and indeed forts, and concluded that the forts should be proceeded with. Government, however, chose to delay work on constructing the forts for another year while it deliberated.

By 1863, events in the American Civil War had swayed opinion in favour of the forts. The Confederate forts defending Charleston harbour had, on 7 April, 1863, repulsed an attacking Union flotilla consisting of seven Monitors and two other ironclads, including the USS Keokuk which sank as a result of damage caused. Parallels were drawn between Charleston and Portsmouth and finally, in the spring of 1864, work on constructing the Solent Sea Forts began in earnest.

Captain Cowper Coles, his role in opposing the Spithead forts complete, incorporated his turret design in the HMS Royal Sovereign. He then campaigned vigorously that he should be allowed to design the future of British warships. He launched a full-force publicity campaign, wooed newspapers and public opinion and engaged in a battle with the Admiralty, and in particular Chief Constructor Sir Edward Reed, forcing the Admiralty to build the ship he designed. This, the world's second ocean going turret-ship after Edward Reed's HMS Monarch (which also incorporated his turret designs), was launched, in 1870 and named HMS Captain. It sank, killing Coles and almost everyone on board in one of the greatest naval disasters of the 19th Century. The following year the Reed's HMS Devastation was launched, a revolutionary warship that was for fifteen years the most powerful warship afloat. HMS Devastation was the first mastless battleship and the predecessor of HMS Dreadnought. She was designed for use in the defence and attack of naval bases against enemy fleets and spent much of her career based in Portsmouth.

Constructing The Forts

The forts were designed by Captain EH Steward, RE and approved by Colonel WFD Jervois, Assistant Inspector General of Fortifications, with the iron armour and iron superstructure designed by Captain Inglis RE and Lieutenant English RE. The chief problem to overcome with the forts' construction would be building the foundations. Colonel Jervois appointed Sir John Hawkshaw, the Civil Engineer behind the Severn Tunnel and London's Hungerford and Cannon Street railway bridges, to be the consultant for the foundations' construction. He proposed three alternatives:

• The creation of an artificial island by dumping rough stone or concrete blocks on a shoal – cost £93,000.
• Laying down a circular iron caisson on the sea bed and surrounding it with stone and concrete blocks – cost £156,000.
• Laying a prepared stone and concrete ring foundation on the sea bed – cost £163,000.

The third approach was adopted for No Man's Land, Horse Sand and Spitbank Forts with the second method later used for St Helen's Fort. Work had begun in July 1861 on forts at No Man's Land, Horse Sand and Sturbridge Shoal, but was suspended between 1862 and 1864 while the political debate took place.

It was in 1864 that it was discovered that a good foundation could not be built on Sturbridge Shoal. This was after £12,000 had been spent on trying to construct the foundations. Senior Naval authorities also expressed concern that any shots fired from a fort located at Sturbridge could potentially hit either the Isle of Wight town of Ryde or Fort Monckton. There was a suggestion of building a fort on the Warner Rock but this was not adopted. A Special Committee was appointed to consider what to do next, which unanimously recommended an additional, but smaller sea fort built on the Spit Bank, 600 yards south-west of the original Spit Bank fort proposal made by the Defences Commission report in 1860. From this position it would tie in the Horse Sand and No Man's Land sea forts with Fort Monckton, Fort Blockhouse and Southsea Castle. The commission also expressed concern that an enemy might attempt to sneak past the forts by keeping close to the Isle of Wight shore. To prevent this they recommended the construction of a fort on the Ryde Sand, 1,200 yards south of the Sturbridge fort. By 1867 it was discovered that Ryde Sand was also unsuitable and a firm foundation could not be made, causing the fort built on the site to be abandoned. Instead, a small fort was built at the edge of the shoals outside St Helens.

Testing in 1865 showed that a 300 pounder Armstrong gun could shatter the granite to be used in the forts within three shots. As a result the forts used a combination of granite and iron, with iron alone being used for key areas.

The foundations 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.

In 1868 the Report of the Committee Appointed to Enquire into the Construction, Condition and Cost of the Fortifications, when investigating Horse Sand and No Man's Land Forts stated:

'Here, then, where the waters of Spithead formerly flowed over shifting sand are steadily growing up the two grandest war structures ever designed, destined to carry many thousands tons of iron, and to have the heaviest projectiles in the world. The best and worst of this too is that is not the slightest probability of their ever firing a shot in anger, provided they are not suffered to fall into decay, because they will answer the highest functions of fortification – the prevention rather than the cure of attack, until the day comes when a mine shaft can be driven from the Continent to the Spithead Forts, or the art of war has arrived at dropping infernal machines or firing huge shells from balloons, Portsmouth may rest content and secure.'

Although in 1862 the estimates to build the larger forts were between £260,000 – £290,000 each, the actual cost of construction was £424,000 for Horse Sand Fort and £462,000 for No Man's Land Fort. The total construction and armament of all four forts came to £1,763,864 at a time when the annual UK Government expenditure was £75,000,000, £15 million of which was spent on the military. Spitbank Fort was completed in 1878, St Helen's Fort in 1879 and the larger Horse Sand and No Man's Land Forts were finished in 1880.

After The Forts' Construction

In 1905 the Owen Committee on the Armaments of Home Ports proposed that a line of concrete blocks should be sunk between South Parade Pier at Southsea and Horse Sand Fort, and from Seaview to No Man's Land Fort. In 1909 this was carried out, and these lie below the water level and prevented enemy ships from entering the Solent from the east without passing between these two forts. Due to the expense concerned of their removal, these still remain today.

By the Great War the forts were expected to deal with the threats of fast torpedo boats and submarines rather than enemy warships. As gun range had increased, the batteries on the Isle of Wight, especially Culver Battery, could deal with approaching enemy vessels. During the Second World War again the threat was seen to be from submarines and light craft. A boom weas rigged between the two main forts with an ASDIC indicator loop laid to detect enemy submarines.

In 1940, when France surrendered, many French naval vessels fled to Spithead, including the Courbet¹⁰. The British Government on 3 July 1940, fearing that the puppet French government would give the French navy to Germany, ordered that all French warships should be seized, demilitarised or destroyed as part of Operation Catapult. For the first, and only, time the sea forts trained their guns on a French vessel, the enemy they had been constructed for. The French ships wisely surrendered, and the forts were not required to open fire.¹¹

The forts throughout the war had anti-aircraft weapons and searchlights during the Battle of Britain. Sadly Portsmouth, as the home of the Royal Navy, was one of the most bombed targets of the Second World War. The forts played a vital harbour defence role throughout the war.

With the end of Coastal Defence in 1956, the forts were no longer needed, and were put up for sale in 1963. Despite rumours that eccentric reclusive rock star millionaires would buy one, Michael Jackson being frequently mentioned, this has not as yet happened, although two of the forts did manage to star in Doctor Who. All four forts have been Scheduled Ancient Monuments since 1967 and since 2008 have been part of a proposal to gain World Heritage Site status, a notoriously long and difficult process.

Last Word

At the time of the sea forts' construction Sidney Herbert, Secretary for War, said in Parliament:

'Years hence, if these works are executed, there will be found gentlemen who will say: "We always predicted that nobody would ever land – that nobody would ever attack these places; See how your money has been wasted." To such remarks, I would retort: "The security which you have enjoyed, the immunity from danger of attack for all these years – has been owing to these very works."'