Box Hill Tunnel (1836-1841)

Box Tunnel is a railway tunnel in western England, between Bath and Chippenham, dug through the Box Hill. It was built for the original route of the Great Western Railway under the direction of the GWR's engineer Isambard Kingdom Brunel.

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, which took five years and cost six and a half million pounds. At the time of opening it was the longest railway tunnel in the 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 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 9th 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 9th 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 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. This is true, but the sun subtends an angle of about half a degree, which is more than the year to year variation, and more than the field of view through the tunnel, so it quite possibly seems to fill the tunnel every year.

It is also asserted at that Brunel failed to account for atmospheric refraction and the effect is visible a few days too early.

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.”

It is tempting to think that with a suitable vantage point, the effect (if not Brunel’s intentions) can easily be checked on April 9th. However, the appropriate point is in the middle of a high-speed railway line and is thus potentially very dangerous. Photographs of the effect have reportedly been taken with appropriate assistance from railway officials.

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. This rumour has circulated for many years, but in fact the only rail entrance to the Tunnel Quarry complex is too small to admit any but the smallest of locomotives.

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. Again, this rumour has done the rounds for years, but seems to have originated from a poor description of the actual entrance, which is just alongside the main Box Tunnel portal, and can easily be seen from passing trains.

In summer 2003, Network Rail cleared vegetation and erected new fencing around the edge of the cutting, and across the top of the tunnel. This would appear to be for safety reasons, but it totally prevents a view of the portal, or the quarry tunnel entrance.

Passing through Corsham is the Great Western Railway line built by the famous Victorian engineer, Isambard Kingdom Brunel, this is the main line from London to Bristol and South Wales.

On the outskirts of the town is the entrance of the railway tunnel, known as Box Tunnel, was at the time it was built between 1836-41, the longest railway tunnel in Europe at around two miles.

At its peak the building work employed some four thousand men and used about a ton of gunpowder a week. Unfortunately a hundred men died during the five years it took to build. The tunnel was opened without any ceremony on 30th June 1841.

The line is dead straight and descends a 1 in 100 gradient from the east. Apparently, although I have never seen it, the sun shines through the tunnel, as it is rising in the east, on or about April 15th each year.

Partway through the tunnel there is a siding into underground workings which was thought to form art of the Royal Navy Supplies Depot at Copenacre. This, allegedly was/is the site to which the Royal Family would flee from London should there have been the threat of nuclear war.