Isambard Kingdom Brunel’s Box Tunnel is celebrated for its engineering significance – and for its entertaining legends.
Driven through the unfriendly Cotswold geology, at the time of construction it was, at 3,212 yards, the longest railway tunnel in the world, though several earlier canal tunnels were longer.
Furthermore, Brunel designed it on a gradient of 1 in 100, descending from east to west. Contemporary critics warned against “the concussion of the atmosphere and the vibration” arising from trains labouring up the grade, and predicted a downhill runaway would leave the tunnel at a speed of 120mph, a calculation which failed to account for friction and air-resistance: Brunel’s more realistic computation arrived at a speed of 56mph.
The tunnel was ready for the first train to run from London to Bristol on June 30th 1841. The west portal, visible from the main road through the village of Box, is an elaborate classical composition. Its arch is far taller than necessary, and the rock-hewn bore funnels to the conventional loading-gauge within. The plainer east portal at Corsham lies in a cutting.
One of the enduring stories about Box Tunnel is that Brunel aligned it so that the sunrise would shine through the dead-straight bore on the morning of his birthday, April 9th. This is within the range of practical possibility, apparently, but difficult in the circumstances to check.
The underground Bath stone quarries which lie under Box Hill to the north of Brunel’s railway tunnel have excited considerable speculation.
Ridge Quarry was used as an ammunition store in the First World War until 1922, and became Central Ammunition Depot Corsham in 1934-6. It was used by the RAF until 1955 and then by the Army until 1964.
A much larger complex comprising some 2¼ million square feet of storage space, based on the former Eastlays, Monkton Farleigh and Tunnel Quarries, was adapted in the 1930s as a huge subterranean ammunition store, Central Ammunition Depot Monkton Farleigh.
This wartime facility was supplied by a narrow-gauge railway and inclines connected to a GWR siding at Shockerwick, just outside the east portal of the main-line tunnel.
In 1940 the Bristol Aircraft Company’s experimental section moved into Spring Quarry, and the Ministry of Aircraft Production built an underground aircraft-engine production plant to avoid disruption from bomb-attacks on Bristol. Despite a reputed final cost of £20 million, the facility allegedly took four years to build, operated for eighteen months up to the end of the War and produced 523 out of a wartime total of 100,932 Bristol aircraft engines.
RAF Box, later known as RAF Rudloe Manor, was established above ground and within a subterranean area known as Brown’s Quarry to act as an important regional headquarters during and after the Second World War.
In the Cold War era part of Spring Quarry was used to build the Central Government War Headquarters, a 240-acre alternative seat for national government in the event of nuclear attack or civil disruption. Capable of accommodating four thousand staff for up to three months, it drew its water-supply from an underground lake and was equipped with generators and temperature-control, the second largest telephone-exchange in Britain and a BBC broadcasting studio.
Peter Laurie’s early study of covert government infrastructure, Beneath the City Streets: A Private Inquiry into the Nuclear Preoccupations of Government (Allen Lane 1970; revised Panther 1979), pointed out that trains running through Box Tunnel audibly traversed a junction, which – he speculated – would allow trains, including the Royal Train from Slough, to disappear into the safety of an underground citadel.
The actual evacuation procedure apparently involved concentrating staff at Kensington (Olympia) station and transporting them by rail via North Pole Junction and Westbury to Warminster, from where they would be conveyed by road to Corsham.
The Prime Minister and his immediate entourage would be the last to arrive, by helicopter directly to Corsham.
The headquarters was apparently abandoned in 2004.
A further facility, the Corsham Computer Centre was established in the former Hudswell Quarry in the 1980s, and remains part of the Bristol Bath Total Facilities Management Project: http://www.indymedia.org.uk/en/2003/11/280247.html.
According to internet sources which may not be up to date, Eastlays Quarry is now a bonded warehouse: http://www.nettleden.com/venues/eastlays-quarry. Monkton Farleigh Quarry was sold in 1976 and briefly opened as a museum in 1984: http://www.theurbanexplorer.co.uk/farleigh-down-tunnel-wiltshire. Ridge Quarry was resold to the original owners in 1975.
In fact, the most accessible information on this former state secret is to be found on the Government website: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/324883/Corsham_Tunnel_version1.pdf.