Looking for further information on the Northern Lines? Try Crownhill Fort or Eastern Flank defences.

The Northern Lines were constructed in the 1860s to provide landward defence for Devonport Naval Base. The north-west flank consisted of four installations – Ernesettle Battery, Agaton Fort, Knowles Battery and Woodlands Fort. Collectively these occupied the high ground to the north of the dockyard between the River Tamar and Crownhill.





By the mid-nineteenth century British defence policy was based upon having a vast navy that outnumbered any opponent. This fleet was comprised of wooden hulled sailing ships that had served the country so well during the Napoleonic wars earlier in the century. However, in 1858 France launched the world's first seagoing Ironclad warship ('La Gloire'; the Glory) instantly outclassing anything in the Royal Navy. In response a Royal Commission was established to assess the new situation and their conclusions, published in February 1860, were that Britain's military forces were insufficient to guarantee an invasion attempt would fail. To mitigate, they proposed that vital facilities across the coastal regions, including the Royal Navy dockyard at Devonport, should be protected by a series of new forts. The proposals were accepted and commenced by the Government of Lord Palmerston. At the time it represented the biggest peacetime military infrastructure project in British history.


The Northern Lines


In order to protect Devonport dockyard, it was necessary to keep any enemy force out of artillery range. Accordingly the defensive perimeter around the dockyard was pushed out to encompass the entirety of Plymouth Sound. Sea defences were constructed at the mouth of the sound but, to prevent an enemy force simply coming ashore nearby and advancing from inland, landward defences were also required. These were divided into three distinct schemes consisting of the Northern Lines, the Western Lines and the Staddon Lines. The former occupied an expanse of high ground to the north of Plymouth stretching from the River Plym in the east to the River Tamar in the west. The primary fortification in this defensive line was Crownhill Fort but it was flanked by a series of secondary forts, batteries and earthworks that acted as a single unified scheme.


The Western Flank


Extending west from Crownhill Fort was Woodlands Fort, Knowles Battery, Agaton Fort and Ernesettle Battery. These outposts provided unbroken coverage of just under three miles between Crownhill and the River Tamar preventing an enemy force from advancing from the north to seize the high ground. Work started on all four structures in 1863 initially under a private contractor. However, the scale of the building project overwhelmed them and the work was ultimately finished by the Royal Engineers. In addition to the forts and batteries, a military road linked all the sites of the northern lines. Where necessary, an earth bank was built to the immediate north of the road to prevent its traffic being visible or vulnerable to enemy fire.


Woodlands Fort

Woodlands Fort occupies a ridge of high ground over the Budcreek Valley. Construction commenced in 1863 and continued through to 1870. It was designed to take eighteen guns most of which were on open batteries although those on the flanks were encased with Haxo casemates. The fort was surrounded by a ditch covered by a caponier and counter-scarp gallery - both of which had gun emplacements and musket slits. A two storey casemated barrack block occupied the northern end of the fort offering accommodation for 100 men. By 1885 the fort had received eight 7-inch Rifled Breach Loading guns but by 1893 half of these had been removed and replaced with three 64-pounder Rifled Muzzle Loading guns. The fort was disarmed by 1900 but it was retained by the military and used as a barracks during World War I. It was sold into private ownership in 1920 but, upon the outbreak of World War II, was requisitioned by the military once more. After the war it was used by the local council as a community centre.


Knowles Battery

Although the ground in front of Knowles Battery was covered by Woodlands and Agaton Forts, the installation was constructed to augment the firepower of those facilities to prevent them from being overwhelmed. Work started on the battery in 1863 and was complete by 1869. The design included thirteen gun positions and, aside from one installed within a Haxo casemate, all were in open batteries. A ditch fronted the battery but, unusually for a fort of this era, there were no counterscarp galleries or caponiers to enable firing into the ditch. To the rear of the four sided battery was a wall equipped with a musket gallery and a two storey guardhouse. The main magazine was under the guardhouse. In 1893 its recorded armament was two 7-inch guns and three 64-pounder guns but it was disarmed by 1900. It served as a barrage balloon site during World War II but after the war the site was converted into a school.


Agaton Fort

Agaton Fort is sited on a salient point offering clear views over Tamerton Lake and the ground to the north, east and west. It was built between 1863 and 1870 and was configured in a polygonal layout. The fort was intended to be fitted with an offensive armament of twenty guns, one within a Haxo casemate and the others in open batteries. Six mortar positions were also added. The defensive arrangements consisted of a ditch surrounding the fort covered by three caponiers and a counterscarp gallery. The fort was never fully armed and in 1893 just three 7-inch Rifled Breach Loading guns and five 64-pounder guns had been installed. Internally the fort had facilities for Officer accommodation and a barrack block for Other Ranks (enlisted personnel). The fort was disarmed by 1900 but served as a military depot through both World Wars. The Ministry of Defence disposed of the site in 1958 and it now serves as a Heavy Goods Vehicle test centre.


Ernesettle Battery

Ernesettle Battery was the western anchor of the Northern Lines and covered the Tamar valley. Work started on the facility in 1863. It built with facilities for fifteen guns situated in open batteries and augmented by six mortar positions. Casemated barracks were provided for sixty men. The fort was never fully armed and in 1885 had just eight 7-inch Rifled Breach Loading guns and two 8-inch Howitzers. The armament outfit was modified soon after and in 1893 just two 5-inch Breach Loading guns and three 64-pounder Rifled Muzzle Loading guns were fitted. The fort was disarmed before 1900 although it remained in military ownership and was used as an anti-aircraft observation post during World War II. Today the site remains part of the Ministry of Defence estate and lies derelict within the Ernesettle Royal Navy armament depot.





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

Historic England (1972). Agaton Fort, List entry 1002613. Historic England, London.

Historic England (2008). Ernesettle Battery, List entry 1003193. Historic England, London.

Historic England (2003). Woodlands Fort, List entry 1002615. Historic England, London.

Hogg, V (1974). Coastal Defences of England and Wales. Newton Abbot.

Kinross, J (1999). The Palmerston Forts of the South West: Why were they built? BBNO Battery Books.

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

Marriott, L (2015). West Country Forts and Castles. Air Sea Media.

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

Moore, D (2010). Agaton Fort.

Moore, D (2010). Ernesettle Battery.

Moore, D (2010). Knowles Battery.

Moore, D (2010). Woodlands Fort.

Pye, A (1996). The Historic Defences of Plymouth. Cornwall County Council.

Wass, S (2010). The Fortifications of Plymouth. Polyobion.

Woodward, F.W (1997). Forts or Follies? Palmerston Forts. Halsgrove.

What's There?

Only Woodlands Fort is accessible to the public. The other three sites that form the western flank of the Northern Lines are not open to the public but the exteriors can be viewed from public rights of way.

The Northern Lines and the Victorian Defences of Plymouth Sound. The Victorian defences were intended to ensure any enemy force was unable to close within artillery range of the important Royal Navy dockyard in Devonport. Crownhill was the lynch-pin of the Northern Lines and further fortifications extended either side with those to the west covering the low ground occupied by Budshead Creek and the Tamar valley. The forts were linked by a military road which, where necessary, was camouflaged by an earth rampart intended to conceal movement along its length. In the wider area there were two other landward defensive schemes - the Staddon Lines (centred on Fort Staddon) and the Western Lines (centred on Tregantle Fort). A significant number of forts also protected the sea approaches. Details of all the forts of Plymouth Sound can be found here.

Woodlands Fort. Woodlands Fort currently serves as a community centre. The site is open access allowing the fort’s ramparts and external defences to be viewed at any reasonable time. However, the exterior is heavily wooded concealing the ramparts. The interior of the fort buildings are not accessible.

Woodlands Fort Haxo Casemate. These arched casemates were frequently installed in forts of the period to provide protection to gun crews. They were normally installed on the flanks where the crews were particularly vulnerable to enemy fire.

Knowles Battery. This battery enhanced the fire-power of both Woodlands and Agaton forts. A swimming pool was installed on the roof after the battery had been converted into a school.

Agaton Fort. The fort dominated Tamerton Lake and the ground to the north. The site is now in use as a Heavy Goods Vehicle training centre.

Ernesettle Battery. This site, often described as Ernesettle Fort, covered the approaches along the Tamar valley. The site is derelict with no public access.

Getting There

The four installations are spaced over a three mile stretch. Visitors can either park at Crownhill Fort and walk between the sites or drive to each location individually.


Crownhill Fort. This fort is well sign-posted from the A38. When open to the public (normally one day per month, Summer only) there is dedicated car park within the fort. Otherwise on-road parking is possible.


Woodlands Fort. Found off Butt Park Road and currently in use as a community centre. There is no car parking in the immediate vicinity but on-road parking is possible on the adjacent streets and there is also a shopping centre nearby (Transit Way, PL5 3TW).


Knowles Battery. This site is now part of Knowles Primary School. The battery guardhouse can be seen from a public park off Ringmore Way. On-road car parking is possible.


Agaton Fort. Found off Budshead Road. The exterior can be viewed but the interior is in use as an HGV test centre. On-road car parking is possible.


Ernesettle Fort. Currently within the perimeter of Ernesettle Royal Navy armament depot and therefore not accessible. The fort's entrance can be seen from a public road off Ernesettle Close.

Crownhill Fort


50.412483N 4.13026W

Woodlands Fort

Butt Park Road, PL5 3SQ

50.413348N 4.154141W

Knowles Battery


50.415704N 4.164617W

Agaton Fort

Ernesettle Lane, PL5 2EY

50.415755N 4.175244W

Ernesettle Battery


50.412482N 4.185066W