Dominating a small rocky island with a strategic position near the entrance to Milford Haven, Thorn Island Fort was built in the mid-nineteenth century to protect against attacks by wooden sailing ships. Within a decade the first Iron-clad vessels were being built and Thorn Island was overshadowed by newer and better armed fortifications constructed specifically to deal with the new threat.



Thorn Island is located on the eastern side of Milford Haven overlooking a large anchorage. A fort was originally conceived for the site as early as 1817 but, with the end of the Napoleonic wars, no action was taken. In the subsequent decades peace with France meant coastal defence was neglected but this strategy was thrown into turmoil with the accession of Napoleon III in 1852. Fears of French re-armament led to the initiation of some coastal defence works with Milford Haven warranting protection due to the existence of the Royal Navy dockyard at Pembroke (which had been established in 1815). Along with Dale Point Fort and West Blockhouse, Thorn Island Fort was one of the fortifications raised at this time to control the entrance to the Haven.  Work started in 1852 although regrettably construction records have been lost. A date above the entrance is marked 1854 suggesting much of the fort had been constructed by this time although it is likely the structure wasn’t fully complete until around 1857-9.


Thorn Island Fort was constructed with a seaward facing battery equipped with nine gun positions which was initially fitted with 68-pounder smooth bore, muzzle loading weapons intended for engaging wooden warships. The landward side was protected by a wall equipped with loopholes for firing small arms. Internally barracks for 55 men and two Officers surrounded a small courtyard. A small magazine provided the single gunpowder store for the facility.


The relatively recent construction of Thorn Island Fort meant it wasn't immediately reviewed for upgrades by the 1859/60 Royal Commission that had been hastily assembled to review coastal defence following the launch, by France, of the first Ironclad warship ('La Gloire'; the Glory). This armoured vessel outclassed anything in the Royal Navy threatening British maritime superiority upon which the nation's prosperity and links with empire depended. At Milford Haven large scale building works commenced as Thorn Island fort was augmented by other installations deeper in the Sound to ensure any vessel that penetrated the outer defences could be stopped. Hubberston Fort, Popton Fort and South Hook Fort were all added at this time. Scoveston Fort was also added to secure overland approaches to Pembroke. Chapel Bay Battery, although part of the 1860 scheme, was not built until 1890. All these forts mounted heavier weapons than at Thorn Island and proposals to upgrade the weaponry during the 1860s seemingly came to northing, presumably due to the difficulty of getting heavy weapons onto the island.


A review of the defences in 1871 initially led to a proposal that Thorn Island Fort, along with Dale Point Fort and West Blockhouse, should be decommissioned due to obsolete weaponry. This was overruled and in 1872 the fort was equipped with five 7-inch Rifled Breach Loading guns whilst retaining four of the existing 68-pounder smooth bore guns. In 1886 though a decision was made to remove the heavy weaponry from the site and in the subsequent years all but two of the 7-inch guns had been removed. The fort was completely disarmed by 1895 and in 1932 it was sold into private ownership. It was used as a hotel during much of mid twentieth century but today is abandoned.




Dyer, N (2014). British Fortification in the late 19th and early 20th centuries. Inky Little Fingers Ltd.

HM Stationery Office (1860). Reports from Commissioners: Sixteen Volumes: Coal Mines, Inland Revenue, Post Office, Ordnance Survey, Defences of the United Kingdom. London.

Lloyd, J.E (1912). A History of Wales. Cardiff.

Moore, D (2011). Arming the Forts. Speedyprint, Gosport.

Moore, D (2010). Thorn Island Fort.

Reid, A (1973). Castles of Wales. Philip, London.

Phillips, A (2011). Castles and Fortifications of Wales. Amberley, Stroud.

Swales-Barker, P (2013). Milford Haven Through Time. Amberley.

Unknown Author (2015). Milford Haven as a Commercial Port and Harbor of Refuge: Its National Importance, Its Claims as a Dépôt for the Western Mails and Terminal Port to the Railways of Great Britain. Forgotten Books.


What's There?

Thorn Island Fort is not open to the public and there is no access to the island. However, the fort can be seen at a distance from the Pembrokeshire Coastal Path which is easily accessible from a nearby car park. Visitors may wish to combine a visit to see Thorn Island with the nearby Church Bay Battery (which is open to the public) whilst the remains of the Tudor Blockhouse, built by Henry VIII, and the 1901 East Blockhouse Battery are also nearby.

Thorn Island Fort Layout. The fort had a seaward facing battery for nine guns whilst a barracks equipped with rifle loops was to the rear. A searchlight emplacement beneath the fort is still visible.

Access. The fort used to be a hotel but is now abandoned with no public access but  it can be seen from the Pembrokeshire Coastal Path. West Blockhouse can be seen in the distance.

Milford Haven. At the time the fort was built (1852), the entrance to the haven was controlled by West Blockhouse, Thorn Island and Dale Point Fort.  The defences of Thorn Island covered the sheltered water which was regularly used as an anchorage and also prevented access further inland towards the dockyard at Pembroke.

Milford Haven Forts. The Royal Navy established a dockyard at Pembroke in 1815 and thereafter Milford Haven was heavily fortified.

Thorn Island Fort. There are also good views of the fort if the Pembrokeshire Coastal Path is followed to the south towards the remains of East Blockhouse.

Getting There

Thorn Island Fort can be seen from the Pembrokeshire Coastal Path. The nearest car parks are at Wavecrest Cafe or Chapel Bay Battery both of which are found to the west of Angle.

Coastal Path Car Park

SA71 5BE

51.686341N 5.106155W

Thorn Island Fort

No Postcode

51.691932N 5.117757W

Church Bay Battery Car Park

SA71 5BE

51.689831N 5.098250W