thumb|right|The west portal

Box Tunnel passes through Box Hill on the Great Western Main Line (GWML) between Bath and Chippenham. The tunnel was the world's longest railway tunnel when it was completed in 1841.

Built between December 1838 and June 1841 for the Great Western Railway (GWR) under the direction of Isambard Kingdom Brunel, the straight tunnel descends on a 1 in 100 gradient from its eastern end. At the time the tunnel's construction was considered dangerous due to its length and the composition of the underlying strata. The west portal is Grade II* listed and the east portal is Grade II listed.

Ammunition was stored near the tunnel during World War II, reusing mine workings. During the 2010s, the tunnel was modified and the track lowered to prepare it for electrification, although in 2016, this plan was suspended.

History

Background

During the 1830s, Isambard Kingdom Brunel developed a plan for a railway running east–west between London and Bristol.

To assess the geology more accurately, between 1836 and 1837, Brunel sank eight shafts at intervals along the tunnel's projected alignment.

Construction

The GWR selected George Burge of Herne Bay as the major contractor, Locally based Lewis and Brewer were responsible for the remainder, starting from the eastern side. One of Brunel's personal assistants, William Glennie, was in overall charge until completion.

Opening

On 30 June 1841, the tunnel was opened to traffic with little in the way of ceremony. A special train departed London Paddington and traversed the whole of the GWR to complete the first rail journey to Temple Meads Station in Bristol in about four hours. The eastern portal at Corsham has a more modest brick face, with rusticated stone dressings. The Society of Genealogists in 2016 suggested the sun shone through the tunnel on 6 April, the birthday of Brunel's sister, Emma Joan Brunel, three years out of four during the 1830s.

Defence use

Starting in 1844, the hill surrounding the tunnel was subject to extensive quarrying to extract Bath stone for buildings. In the run-up towards the Second World War, the need to provide secure storage for munitions at distributed locations across the UK was recognised. During the 1930s, a proposal to create three Central Ammunition Depots (CADs) was submitted. One was to be located in the north at Longtown, Cumbria; one in the Midlands (Nesscliffe, Shropshire); and one in the South of England at Tunnel quarry, Monkton Farleigh and Eastlays Ridge.

thumb|right|250px|The east portal with the quarry entrance to Tunnel Quarry clearly visible on the right

During the 1930s, Tunnel Quarry was renovated by the Royal Engineers as one of the three major stockpiles. During November 1937, the GWR was contracted to build a raised twin-loading platform at Shockerwick for Monkton Farleigh and two sidings branching from the Bristol–London mainline just outside the tunnel's eastern entrance at . below and at right angles to this point, the War Office had built a narrow-gauge wagon-sorting yard which accessed a tunnel, built by the Cementation Company, descending at a rate of 1 in 8.5 to the Central Ammunition Depot in the former quarry workings. The logistics operation was designed to cope with a maximum of tons of ammunition per day.

The CAD was closed at the end of the war but was maintained in operational condition until the 1950s. The sidings were cleared, and saw no further use until the mid-1980s when a museum was opened on the site for a short period. During the post-war years, portions of the ammunition depot were redeveloped for other facilities, including the Central Government War Headquarters, RAF No.1 Signal Unit, Controller Defence Communication Network and the Corsham Computer Centre.

Electrification

The tunnel was planned to be electrified by 2017 as part of the Great Western Electrification Programme. During the summer of 2015, the tunnel was closed for six weeks for preparatory work including lowering the track by roughly and replacing of cabling in advance of the catenary infrastructure being installed. However a November 2016 announcement stated that the plan to electrify the mainline from Thingley Junction (near Chippenham) to was delayed indefinitely.

Geographical location

  • East portal:
  • Ventilation shaft:
  • Ventilation shaft:
  • Ventilation shaft:
  • Centre of tunnel:
  • Ventilation shaft:
  • Ventilation shaft:
  • West portal:

See also

  • List of tunnels in the United Kingdom
  • Stapleford Miniature Railway 1/5 railway featuring stone replica of Box tunnel

References

Citations

Bibliography

  • Network Rail Virtual Archive: Box Tunnel, engineering drawings of tunnel
  • Subterranea Britannica entry on the Corsham bunkers
  • Brunel portal
  • Tunnel does align, but 3 days before Brunel's birthday; however the sky is not visible through it, detailed analysis of the alignment
  • Wiltshire's Secret Underground City: Burlington Articles, interactive map and video tour from BBC Wiltshire
  • The light at the end of the tunnel. How Brunel designed his memorial into the Box Tunnel, which is aligned with the sun on his birthday, 9 April.