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GCHQ has revealed the locations of five secret sites it used during the Second World War and Cold War.

The sites have long since been closed down, but were used for identifying secret communications between Adolf Hitler and his field marshals, as well as intercepting a fax for the first time in British intelligence history.

Teams based at the five previously covert locations also helped the Cold War efforts against the Soviet Union by intercepting communications from its army, navy and air force.

Croft Spa, Scarborough

(Image: Thomas Tolkien / Wikimedia Commons)

Around 20 people worked in the countryside near the North Yorkshire seaside town between 1940 and 1975.

It was a direction-finding station that worked in conjunction with other sites to pinpoint the location of enemy signals from ships in the North Sea.

The staff worked in the huts pictured at the top of the story and frequently had to ask farmers to stop their work without given them a reason - which was to ensure noise from their machinery did not interfere with the collection of the important communications.

Marston Montgomery, Derbyshire

(Image: GCHQ)

This site, made up of a series of wooden huts in a remote location, was operational between 1941 and 1947 with around 100 people based here.

Set us as an outstation of RAF Cheadle, the head office for the RAF's Sigint unit, Marston Montgomery was the home of technical radio and operator finger-printing.

Staff would listen to at least 25 different operators each, identifying individual radio signals - for example by the speed that people would type out Morse code.

Once enemy operators were identified, this information could be used to piece together troop movements.

This was the first GCHQ base to have a woman commander, 2nd officer Pamela Pigeon.

It was dismantled after the war.

Ivy Farm, Kent

(Image: GCHQ)

Operational in the Second World War, Ivy Farm, in Knockholt, Kent was home to the headquarters for the Foreign Office Research and Development Establishment, which has since moved to Cheltenham. Staff numbered between 60 and 100.

Rather than monitoring voice or Morse code, for the first time in UK intelligence history staff at Ivy Farm investigated what is known as 'noise' - sound which does not carry human communications.

(Image: GCHQ)

Such noise was found to carry the secret to Adolf Hitler's most secure communications with his field marshals across Europe. It used encrypted teleprinter technology, which was many more times secure than the Enigma code.

Staff successfully intercepted and isolated messages within the 'noise' which was passed on to Bletchley Park to decipher and ultimately lead to the creation of the world's first computer Colossus.

Ivy Farm was also responsible for the first-ever UK interception of a fax.

A Japanese press attache in Berlin had sent a fax featuring details of US bomber squadrons and formations to a Tokyo-based press agency, intended for the Japanese military so they could better attack the US air force.

This information was passed to US allies so they could adapt their tactics accordingly.

Chesterfield Street, London

(Image: Google Maps)

The site in Mayfair began operations with around 10 people in 1944 and eventually had up to 60 staff.

The office block housed the beginnings of what became GCHQ during the Cold War.

All Soviet targets were worked on from the office and the first interception of enemy army, navy and air force communications was achieved here.

The office stayed open until 1953 when the Palmer Street office near St James' Park was opened to consolidate all London operations.

Bill Bonsall joined as one of the 10 first employees in 1944, mainly working on German air force intercept. He went on to become director of GCHQ in 1973.

The Chesterfield office is now the site of the High Commission of The Bahamas.

Abbots Cliff House, Kent

(Image: GCHQ)

Operational between 1940 and 1945, Abbots Cliff House at Capel le Ferne near Folkestone had between 50 and 60 staff.

The base collected Very High Frequency (VHF) communications from Germany directing aircraft or fast moving E-boats in the English Channel.

VHF has a very short range which meant that German-speaking linguists, mainly young women, were sent to the front line to live-log the communications.

This type of interception had never been done before for voice communications and the tactical nature of this job meant that every day the information collected by these workers was helping to protect British pilots and sailors.

German forces would try to capture British pilots downed over the Channel and information from Abbots Cliff House would have helped save some British pilots during the war.

The building still exists today and overlooks the coast to France.

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