World War II Tunnels at Porthcurno Telegraph Station St. Levan, England

Text courtesy of Historic England. © Crown Copyright, reprinted under the Open Government License.

ST LEVAN

1621/0/10008 THE VALLEY 17-SEP-08 WORLD WAR II TUNNELS AT PORTHCURNO TEL EGRAPH STATION

II* Underground wartime international communications centre built 1940-41 for Cable and Wireless. The structure consists of a pair of interconnected, rock-cut, concrete block lined, parallel tunnels cut into the hillside behind Eastern House, protected on the west by concrete blast walls. Ventilation vents built into these walls are the outlets for the internal air-conditioning system. Normal access was provided through two concrete block lined passages leading to a pair of blast doors. An escape passage with flight of stairs leads to a protective concrete structure with further blast doors on the hillside to the E.

Interior: Within the tunnels there is a concrete block building with timber roof and planked ceiling. In the S tunnel a small section of this building has been cut away and replaced with glass, allowing visitors to appreciate the construction details. Leading along the centre of the roof throughout the building is an air conditioning duct with conical vents at frequent intervals. Hanging from the ceiling throughout most of the building are original light fittings. In the W part of the N tunnel is an emergency electricity generator, alternator and fuse panel manufactured by Lancashire Dynamo & Crypto Ltd. in 1941. Access to the space between the tunnel and building was provided by a ladder formed by rungs attached to the outer wall.

A range of museum displays including original telegraphic instruments now occupies the tunnels.

History: The electric telegraph was introduced in the 1830s. Samuel Morse's dot-dash code evolved from 1835, and the technology of long-distance telegraph communication developed rapidly thereafter, with the underground and submarine cables being developed from the 1850s. The first transatlantic telegraph cable was a British and American enterprise with the cable running from Foilhommerum, Valentia Island in western Ireland to Heart's Content in eastern Newfoundland. The first attempts met with limited success and it was not until 1866 that a lasting connection was achieved.

The telegraph station and training school at Porthcurno were established in 1870 when a cable from Carcavellos in Portugal laid by the Falmouth, Gibraltar and Malta Telegraph Company arrived on the beach. This cable was the final link in a chain of cables leading from Bombay in India. The importance of this link at the height of the British Empire cannot be overstated. The original intention was to bring the cable ashore at Falmouth, but the sheltered, sandy beach at Porthcurno was felt to be a much more reliable option. The original telegraph station buildings were situated at and around what was to become known as Zodiac House. In 1872 the original company merged with three others to form the Eastern Telegraph Co. Ltd. A year later another cable was laid to Vigo in Spain and staff cottages were built in the valley. During the 1870s experiments to improve the quality and efficiency of the process were conducted at Porthcurno and were ultimately responsible for world-wide improvements in telegraph communication. In 1878, the third cable arrived at Porthcurno from the Isles of Scilly and a fourth to Gibraltar in 1887. The tennis courts were established on rented ground in the 1880s and separate accommodation for the Superintendent (Mercury House) was built in 1896. In the early part of the C20 considerable expansion of the operation saw many more cables brought into the valley. In 1904 the telegraph station moved across the valley to new purpose built fire-proofed accommodation at what was to become known as Eastern House. The arrival of another cable, this time to Fayal in the Azores in 1906 led to Eastern House being extended northward. In 1928 a conference held in London recommended an amalgamation of all the cable and wireless interests within the Empire