Box Tunnel

The tunnel is 2939m (1mi 1452yd) in length, straight, and descends a 1 in 100 gradient from the east. Construction started in 1836, and the tunnel opened in 1841. The lives of about 100 navvies (railway construction workers) were lost during construction. At the time of opening it was the longest railway tunnel in world, though Sapperton canal tunnel was longer. The dramatic western portal, near Box, is designed in the classical style, but the eastern portal, at Corsham, has a plain brick face. When the the two ends of the tunnel were joined underground there was found to be less than 5cm (2in) error in their alignment.

Brunel's Birthday

There is a story which states that Brunel deliberately aligned the tunnel such that the rising sun is visible through it on April 9 each year, his birthday. Opinions vary widely as to whether this is true. R. Angus Buchanan writes in Brunel: The Life and Times of Isambard Kingdom Brunel ISBN 1-85285-331-X (p.269, n.48):

The alignment of the Box Tunnel has been the subject of serious discussion in the New Civil Engineer and elsewhere. I am grateful to my friend James Richard for making calculations which convinced me that the alignment on 9 April would permit the sun to be visible through the tunnel soon after dawn on a fine day.

On the other hand, it is asserted at http://venus.soci.niu.edu/~archives/TOMPAINE/feb99/0023 that it impossible to guarantee the effect on a particular calendar day, because the angle at which the sun rises on a given date varies slightly with the cycle of leap years.

It is also asserted at http://www.magonia.demon.co.uk/news/tunnels (about two-thirds of the way down the page) that Brunel failed to account for atmospheric refraction and the effect is visible a few days too early. (This page is mainly concerned with another story: that there is a junction within the tunnel leading to a secret bunker - see below.)

Buchanan concludes (ibid., p.226):

...I have found no documentary evidence for the often-repeated story that Brunel aligned the Box Tunnel so that the rising sun shone through it on his birthday, even though careful examination shows that it could indeed do so, and it is certainly a good story.

A Secret Tunnel?

It is also sometimes claimed that there is a secret junction and spur tunnel within Box Tunnel, leading to a secret bunker, or possibly to a "strategic reserve" of mothballed steam locomotives to be used in the event of a major oil crisis or nuclear war.

In fact, the tunnelling at Box revealed the existence of large amounts of good quality Bath stone in the hillside, and Tunnel Quarry was opened in 1844 to take advantage of this, with its entrance alongside the eastern portal of Box Tunnel, and a branch line running into it. This extensive stone mine was taken over by the government for use as an ammunition dump (with an underground station) during and after World War II, and was connected to other underground facilities cut into the same hill. The cold war bunker known as "Burlington" and intended to be used by politicians and the Royal Family in the event of nuclear war is in another cavern nearby. Tunnel Quarry is now closed and its entrance hidden by overgrowth. There is no reason to believe that there is a connection actually within Box Tunnel.

See:

• http://www.subbrit.org.uk/rsg/sites/c/corsham/
• http://www.follybooks.freewire.co.uk/
• http://www.magonia.demon.co.uk/news/tunnels