Summary

A late C19 mobilisation centre which was modified from the late 1930s for rocketry research, and in the late 1940s for the top-secret development of Britain’s first atomic bomb.

Source: Historic England

Details

Fort Halstead is located on the crest of a steep chalk escarpment of the North Downs, to the north-west of the village of Dunton Green and overlooking the Darenth Valley. The fort is polygonal in plan and is surrounded by an earth rampart and a deep external ditch with a sloping earth counterscarp and concrete revetted scarp. The ditch is extant for much of the circuit except at the north-west and west of the fort where is has been infilled although survives as a buried feature. Within the base of the ditch to the south is a brick compound built against the concrete revetment and containing a domed structure of unknown function.

The original access to the interior parade is from the north-west where two of the eleven angles of the fort form a re-entrant. There is a later additional entrance to the south-west linking the fort interior with the wartime experimental rocket filling area to the south-west of the fort. This entrance is shown on an aerial photograph of 1952 but not on one of 1946. The original entrance is via a north-south causeway over the ditch which is flanked by low concrete walls topped with original metal fence posts and a modern wire mesh fence. Originally the whole fort would have been enclosed within a high steel fence with gates hung on steel girders at the entrance (traces of which survive). Where the roadway cuts through the rampart it is flanked by concrete retaining walls.

The rampart is a massively built earthwork, part revetted in concrete, with a parapet, banquette (infantry fire-step) and terreplein (a platform or level surface on which heavy guns are mounted). Along the crest of the rampart are surviving traces of the brick-revetted emplacements for machine-guns positions some with small expense magazines set into the rampart. (Nine appear to be shown on the Bradshaw plan of 1922). At the north-east corner of the fort is an additional structure of Second World War date, possibly a fire watchers post. This is of brick and concrete construction and has a protected entrance. A number of traverses project from the internal face of the rampart, the majority of which are mounded over magazines or casements. There is a linear central traverse which crosses the parade in a broadly north-south axis, centrally to the fort, curving to the north-east at its northern end.

There are three magazines cut into traverses to the north-east (Building F3), south-east (Building F5) and south (Building F6). These are concrete built and cellular providing chambers for the storage of ammunition (shells and cartridges). All are provided with safety lamp recesses with glazed and metal grill covers: these recesses ensured that the flame of the lamp was separated from, but lit, the ammunition storage areas. The earth-covered reinforced concrete roofs have an added layer of flint within the earth cover designed as a bursting layer to detonate any enemy shell before it reached the magazine.

There are also three sets of casemates, to the west, north and east. All the casemates are concrete built and cellular although with some discreet elements in brick. The northern (Building F2 which was not available for inspection) is cut into the northern end of the central traverse. In plan this has nine casemates running broadly north-south with a covered access corridor to the west. An associated ammo store is cut into the rampart to the north-west across the access passage. The eastern group (Building F4) is cut into the rampart. These casemates were available for inspection and have access steps leading down from the north parallel to an access ramp. To the east of the covered corridor are the four chambers. These have solid planked double doors with timber-framed overlights. The passage is now (2012) covered in a clear plastic corrugated roofing material and there is extensive pipework in the corridor above head height. The western and largest group of casemates (Building F8) comprises 17 chambers with a reinforced concrete roof, and also two ammunition stores for small arms (Buildings F7 and F9) set west of the concrete revetted access passage within the rampart. It was originally earth-covered but this has been removed. Two flights of steps lead from the passage up onto the rampart. Access was prohibited at the time of inspection but it is understood that these casemates have experienced some minor alterations for use from the mid C20 onwards but that their C19 form remains legible. Photographs from c1989 show that the corridor, its roof covering and chamber entrances are of the same form as Building F4. However, many of the entrance overlights had been bricked-up at that time. The same photographs suggest that the internal chamber divisions are at least partly brick built.

At least one C19 hydrant survives within the fort.

EXTENT OF SCHEDULING

The monument excludes all buildings and structures constructed post-1900 (although the ground beneath them is included), the one exception being the Second World War firewatcher’s post on the north ramparts which is included. For the avoidance of doubt Buildings F2, F3, F4, F5, F6, F7, F8 and F9, which are all part of the C19 fort, are included in the scheduling as are any post-1900 modifications to these structures.

Source: Historic England

Reasons for Scheduling

Fort Halstead, a late C19 mobilisation centre which was modified from the late 1930s for rocketry research, and post-war for the top-secret development of Britain’s atomic bomb, is scheduled for the following principal reasons:
* Rarity and form: one of 13 purpose-built mobilisation centres nationally erected in the late C19. Fort Halstead was the largest (and most expensive) built and is one of only four designed for artillery deployment. Also, a highly significant site in terms of mid-late C20 rocketry and atomic bomb research and development;
* Survival and diversity: a mobilisation centre which survives in largely intact form. Although a section of late C19 ditch has been infilled, this survives intact as a buried feature. The fort also includes evidence for the site’s later research and development role with limited alteration of some of the casements and magazines for this later use; this modification adds to the fort’s interest;
* Documentation: the site has the potential to significantly enhance our understanding of the development and operation of the late C19 mobilisation centres constructed to defend the capital, also to aid our understanding of the nationally significant atomic bomb research and development undertaken here;
* Group value: with listed buildings within and immediately outside the Fort representative of the site’s later role as a military research establishment.

Source: Historic England

Sources

Books and journals
Barker, L, Pattison, P, North Weald Redoubt, Essex , (2000)
Cathcart, B, Test of Greatness: Britain’s struggle for the atomic bomb , (1994)
Clive, R, Fort Halstead: A Celebration of the First 100 years, (1977)
Cocroft, W D, Dunton Green, Sevenoaks, Kent: A Brief Assessment of the Role of Fort Halstead in Britain's Early Rocket Programmes and the Atomic Bomb Project , (2010)
Saunders, A, Smith, V, Kent's Defence Heritage, (2001), 234-242 and gazetteer reference KE80
Hamilton-Baillie, J, 'Country Life' in London’s Victorian Forts, , Vol. Nov 13 1986, (1986 ), 1560-2
Smith, V, 'London Archaeologist' in The London Mobilisation Centres, , Vol. 2, No 12, (1975), 244-248
Smith, V, 'Post-Medieval Archaeology' in Chatham and London: The Changing Face of English Land Fortification 1870-1918, , Vol. 19, (1985), 105-149
Other
Brunton Boobyer Partnership, Notes on the History of Fort Halstead, 1984,
Cocroft, WD & Fiorato, V, Fort Halstead: a summary history, 2012,
English Heritage Archive select photographs:
Aerial Photograph (October 1946): RAF CPE UK 1789 11 Oct 1946, frame 4473
Aerial Photograph (April 1947): RAF CPE UK 1982 11 April 1947, frame 1110
Aerial Photograph (May 1952): RAF 540/731, 15 May 52, frame 4075
,
Griffiths, N, , R.A.R.D.E. Fort Halstead: a short history, 1984,

Source: Historic England