The GCHQ building in Cheltenham (Picture: PA).
The head of Government Communications Headquarters (GCHQ) says technology is offering "unique challenges" for the future, as the facility marks 100 years in operation.
The intelligence and security organisation has been instrumental in defining moments throughout wartime and peace, but director Jeremy Fleming has been looking forward, rather than back.
Marking its centenary with a series of events, including an exhibition at the Science Museum in London, he says GCHQ is also looking ahead to situations of "enormous complexity".
Mr Fleming said: "We're living through a period of accelerated change in terms of technology: that comes with huge advantages and unique challenges for society. It means the way we work is changing.
"But throughout our history we have always tackled developments in communications to stay one step ahead.
"We have always risen to the challenge that change brings."
Representatives from the international Five Eyes intelligence alliance - the UK, US, Canada, Australia and New Zealand, will come together today to celebrate the past and present success of GCHQ in national security.
Mr Fleming described Five Eyes as an "extraordinary partnership that plays a pivotal part in global security and stability, and still stands strong today".
As part of the centenary celebrations, GCHQ has revealed five secret sites where historic intelligence work has taken place.
A farm-house outside London and a manor on the White Cliffs of Dover are among the locations identified.
At the sites, Nazi wartime communications were listed as some of the wartime messages identified and intercepted.
GCHQ was formed on 1 November 1919 as a peacetime "cryptanalytic" unit - made up of staff from the Admiralty's Room 40 and the War Office's MI1(b).
During the Second World War, personnel moved to Bletchley Park where they decrypted German messages, most famously by breaking the Enigma code.
The agency's best-known former member and wartime code-breaker is Alan Turing, who was instrumental in cracking the Enigma code and will appear on the next £50 note.
Prime Minister Boris Johnson said: "GCHQ has been home to some of the brightest people in the country who quietly, and without fanfare, work day and night to keep us safe.
"The centenary provides an opportunity to recognise their enormous contribution to the security of the UK."