The Prince of Wales has spent the day visiting RAF Menwith Hill in North Yorkshire.
The base is used by personnel from the US National Security Agency (NSA), as well as staff from the UK Government Communications Headquarters (GCHQ).
He addressed staff, met workers and toured the operations centre.
The site was established in 1954 to act as a "communication intercept and intelligence support service" for both the UK and America.
RAF Menwith Hill is known for its large radomes, which are nicknamed the golf balls because of their white, dimpled appearance, and which were designed to shield and protect radar equipment.
Sqn Ldr Geoff Dickson, commanding officer at the site, said : "The delight on the faces of our employees reflects the honour we all feel in seeing His Royal Highness come to RAF Menwith Hill to see first-hand the work that we do, particularly in the year in which we are commemorating 60 years of operations."
During his trip to North Yorkshire, Prince Charles also met soldiers from the Royal Dragoon Guards at Catterick Garrison.
The prince is Colonel-in-Chief of the British Army's armoured cavalry regiment.