Submarine Mine Observation Station and Observation Post

Summary

A submarine mine observation station of 1896, with an observation post of c.1910 to the immediate north, historically associated with a Defence Electric Light emplacement (qv.) and Fort Bovisand (qv.)

Reasons for Designation

The Bovisand Submarine Mine Observation Station and Observation Post are listed at Grade II, for the following principal reasons:
* Historic interest: they have strong cultural and historical significance, within both a local and national context, marking the late-C19/ early-C20 use of mines to defend against submarine attack;
* Date: the observation station dates from the relatively short construction period of such structures in the late C19;
* Rarity: few submarine mine observation stations and search light assemblages survive well.
* Intactness: despite some decay to the fabric, it remains largely intact and legible.
* Group value: the structures form an historic group with a Defence Electric Light (DEL) emplacement, Fort Bovisand and related structures, and with the Staddon Heights military landscape as a whole.

History

The fortifications around the port of Plymouth and the naval base at Devonport have expanded and been modified steadily as weapons technology has advanced, and as military threats have changed. In the late C15 and early C16, small blockhouses were built along the cliffs of Plymouth Hoe. By 1600, Plymouth Fort had been built where the Royal Citadel now stands, and Drake's Island was better fortified. The earliest known fortifications at Staddon Heights are shown on a map of c.1587, where a barricade and cannon are depicted. During the C18, the almost continual wars with France saw the expansion of Plymouth's defences, including on Staddon Heights in the east, and Maker Heights in Cornwall. Staddon Battery was built in 1779 to protect the approach to Plymouth Sound from the east, and had a clear view over the approach to Plymouth Sound by sea. A breakwater was built at the entrance to the Sound, to the designs of the renowned engineer and bridge builder John Rennie (1761-1821), with construction beginning in 1811. The mile-long protective breakwater, his grandest executed work for the Admiralty, was not completed until 1848, although its scale was admired by Napoleon when he arrived as a prisoner at Plymouth in 1815, to Rennie's gratification. The breakwater was completed by his son, Sir John Rennie (1794-1874), who also built Bovisand Pier and Harbour (1816-24), which watered ships via a nearby reservoir, thereby easing the increasing traffic congestion in the port of Plymouth. Staddon Battery was disarmed in 1853 following the completion of Staddon Point Battery (qv.) to the south in 1847, although it may have continued to be used by the military after this time.

The mid-C19 was marked by a period of growing political and military concerns over French foreign policy and the development of an arms race between the two nations. The Royal Commission of 1859 considered the need for modern defences to protect Royal Dockyards, ports and arsenals; their recommendations for Plymouth resulted in the completion of six new coastal batteries and a ring of eighteen land forts and batteries. These were based on three principal forts which are located at Tregantle on the Cornish side of Plymouth harbour, and Crownhill and Staddon on the Devon side. The land forts and batteries were linked by a system of military roads protected from the likely direction of attack by earth traverses and cuttings. Fort Staddon was built between 1861- 69 as the main work of the Staddon Heights defences. It occupies the highest point between valleys leading to Hooe Lake and Bovisand, and lies between Fort Stamford and Brownhill Battery. Further defence works included Breakwater Fort (qv.) from 1861, which was built 100 yards behind the centre of the breakwater, and Fort Bovisand (qv.), built below Staddon Point Battery between 1861 and 1871. Probably during the 1860s, a covered way was created to link Staddon Point Battery with Staddon Battery and Watch House Brake Battery (1869), both to the north. It would also eventually connect with Staddon Heights Battery (1893).

Searchlights were used for military purposes from the 1880s and by the turn of the century their usefulness as part of coastal defences was firmly established. They were primarily used to spot and track approaching enemy vessels. Their deployment was of particular use when tackling the threat of submarine attack, a form of marine vessel that developed rapidly in the later C19. By 1880 the key English strategic target of Plymouth was defended by anti-submarine mines laid between the Breakwater and Bovisand Pier (qv.) to the east, and Fort Picklecombe (qv.) to the west. In 1885 three pairs of Hotchkiss 6-pounder QF guns were proposed for Fort Bovisand in order to defend the minefield between Bovisand and the Breakwater. In 1896 the original guns on the upper level of Staddon Heights Battery (also called the 'old fort' or 'top fort') came back into use as the 9-inch guns in the fort casemates were removed. However, by 1898 the War Office had ordered the construction of new emplacements on the lower level of the battery to accommodate four new, quick-firing,12-pounder, 12cwt. guns. The order also included the construction of a number of searchlight stations, or Defence Electric Light emplacements (DELs). In the meantime, a submarine mine observation station had been built, in 1896, to the north of the fort on the edge of a former quarry. Between 1898 and 1900, four DELs were built to light the minefield: two on the end of Bovisand Pier, and two on the coast below the observation station. Three vaulted chambers in the fort, under the road to the rear of the casemates, were adapted at this time, for use in conjunction with the observation station and DELs. Two further DELs were built in c.1910 to the south-east of the fort. By 1910, an observation post was present to the immediate north of the observation station, and it is marked as a Directing Post on a plan of 1911. This post and the observation station were accessed from a covered trackway above, which since the1860s had linked Staddon Battery with the other batteries on the ridge. A path and flight of steps linked the observation station to the DELs on the shore below. All the DELs were probably powered by diesel engines in casemate No.1 and No.2 in the fort. In 1905, the First Sea Lord, Admiral Fisher, ordered the cessation of the submarine mining of harbour entrances, and so presumably the observation station became redundant at this time. The construction of the DELs to the east of Fort Bovisand in c.1910 shows that searchlights remained in use to protect against surface vessels. They were utilised in World War One when Plymouth Sound was infiltrated by German U-boats. Booms were spread across the Sound entrances, one of which had its shore end at Bovisand. The south DEL on the shore was still in use in 1915, and the searchlights at the seaward end of the pier were relocated to a blockhouse at its landward end in that year.

During the Second World War, the defences were upgraded when a number of batteries were reconfigured, improved artillery was installed, and new ancillary structures such as Coastal Artillery Search Lights (CASLs) were built. The guns and searchlights at Bovisand were removed in 1957 when the fort closed as a military establishment. While some of the buildings on the site have found new uses, many of the smaller structures have remained out of use since their original function has become obsolete. One of the DELs at the end of the pier was demolished in the 1970s and the remaining structures have been adapted for other uses. Part of Fort Bovisand, and the pier and harbour, have served as commercial diving schools for periods from 1970 to the early C21.

In 2013, the north DEL on the shore is partially collapsed, and the steps behind the south DEL are collapsing due to the unstable cliff face. A bridge between the DELs was demolished by the 1990s, and the roof of the observation post above was partially collapsed by this time. The observation station itself is covered by undergrowth. The two DELs to the east of the fort are no longer extant. Four of the CASLs remain intact.

Details

A submarine mine observation station of 1896, with an observation post of c.1910 to the immediate north, historically associated with a Defence Electric Light emplacement (qv.) and Fort Bovisand (qv.)

MATERIALS: both structures are of shuttered concrete. The observation station is built around an earlier limestone building, and has iron fittings and armour plating.

DESCRIPTION: the observation station is a semi-sunken concrete structure consisting of a pair of observation cells, each approached by steps at the rear end. Each contains a slab containing a recess or instrument socket. The roofs are protected by armour plating and the viewing slits have sliding iron shutters.

The observation post is a small rectangular concrete structure with a door at the rear and a broad opening to the front. The concrete roof is partially collapsed at the front.

Sources

Books and journals
Clamp, A L, Bovisand - Once a Fort Now an Underwater Centre, (c.1990)
Clamp, A L, Bovisand - Once a Fort Now an Underwater Centre, (c.1990), 19
Pye, A, Woodward, F, The Historic Defences of Plymouth, (1996)

End of official list entry

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