09 February 2010

Callsign GBZ

Criggion Radio Station, callsign GBZ, was operated by the Post Office and, after privatisation of telecommunications in 1984, British Telecom. It passed coded Admiralty, and later Ministry of Defence, instructions to the Navy's ships and submarines, including those carrying Trident. During WWII, Criggion played its part in the sinking of the battleships Scharnhorst and Bismarck, and the capture of the tanker Altmark. During the Cold War the site was a Category A target for the Soviet Union. It was likely the channel by which Margaret Thatcher's 1982 instruction to sink the General Belgrano was passed.

Criggion was planned in 1940 as a back-up to the station at Rugby, as there were concerns that the latter could be damaged by stray bombs intended for Coventry. When built, it consisted of two high frequency (HF) stations, a low frequency (LF) station, and a very low frequency (VLF) station, spread out across what used to be a 400 acre site. The site was chosen because steel was in short supply at the time, and only three 680 foot pylons could be found, originally bound for the Trincomalee naval station, Ceylon (now Sri Lanka). A steep hill next to level ground to provide the fourth and fifth anchorages for the VLF aerial was required. Breidden Hill, at about 900 feet, was perfect for this, and the nearby Severn could provide water for the heat exchangers used to cool all the valves.

Building commenced in 1941. The first HF transmitter was operational by September 1942. Whilst still being tested, in early 1943, the VLF transmitter at Criggion had to be hastily commissioned to take over from Rugby, whose similar transmitter had been damaged by fire (it was out of action for six months). Additional HF transmitters were installed between 1943 and 1945. The military facilities were further added to during the Cold War. A larger VLF aerial was installed in 1967-68, slung from 720 feet stayed masts, the concrete blocks to support which can still be seen.

The station also carried civilian traffic. Until the Atlantic cable was laid, Criggion carried all telephone circuits to America. As cables and satellites proliferated, the various HF facilities were dispensed with, and all 25 HF transmitters and their associated aerials were decommissioned by 1971-72. The facilities were upgraded in 1983 and as recently as 1991, the VLF and three LF transmitters continuing in service until 31 March 2003. The pylons and masts for the VLF and LF aerials were brought down with explosives within months of the site's closure.

The buildings are fascinating. Of course, much of the equipment was removed when the site closed, and subsequently the place has been looted, no doubt for the miles of copper cable that it must have contained, but there are clues to its past. The built-up foundations were designed to accommodate the flooding of the Severn. In the early days transport around the site came in the form of a tractor and trailer, but later a DUKW and an amphibious jeep were provided. Garages, a pumping station, and what look like living accommodation provide a feel for how busy the place must have been at its height, when 160 people worked here.

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