GCHQ marks 75th anniversary of the UKUSA agreement

We have today released never-before-seen details from the diary of our first Director revealing the steps taken to forge the UKUSA intelligence sharing relationship.

Marking the 75th anniversary today of the UKUSA agreement, the diary sheds new light on the secret visits between the agencies’ leaders, paving the way for the strongest intelligence alliance in the world.

As the threat from the Nazis was replaced by a new one from the Soviet Union, the agreement formed the basis for co-operation in the Cold War. The document, signed in Washington in March 1946, sets out the post-war arrangement for sharing intelligence between the UK and the United States. In the 10 years that followed, Australia, Canada and New Zealand joined making up The Five Eyes alliance.

In one diary entry on 10th February 1941 Commander Alastair Denniston, then Head of the Government Code & Cypher School, notes: “The Ys are coming!” (Y being shorthand for Yanks) referring to the legendary ‘Sinkov Mission’, which saw a group of Americans take the dangerous and top-secret journey across the Atlantic to Bletchley Park.

Commander Denniston famously told his assistant Barbara Abernethy of their pending arrival: “There are going to be four Americans who are coming to see me at 12 o’clock tonight. I require you to come in with the sherry. You are not to tell anybody who they are or what they will be doing.”

The relationship flourished during the visit and intelligence was shared, including Britain’s greatest secret – the Bombe machine, designed by Alan Turing and Gordon Welchman to break the German Enigma code.

The visit to Bletchley marked a turning point in the relationship. Denniston’s diary entries show that shortly after the Americans returned, he followed them across the Atlantic. He met with, among others, his counterpart William Friedman, Chief Cryptanalyst in the Signals Intelligence Service, with references recorded of at least two other meetings at locations across New York.

The intelligence coalition first established in these meetings underpins the UKUSA agreement that has stood the test of time, proving invaluable to each country’s national security. One example includes when intelligence reports provided by GCHQ led directly to the de-escalation of the Cuban Missile Crisis. The team at GCHQ’s base in Scarborough had been tracking High Frequency (HF) radio frequencies used by Soviet merchant shipping in the Atlantic. They picked up the first signals which revealed the ship carrying missile cargo had turned around and was heading back to Russia. The relationship goes beyond the sharing of data and intelligence reporting. For decades both agencies have shared roles in each other’s organisations and work together in all areas of operations which help to keep both countries safe.

In a joint statement Director GCHQ Jeremy Fleming and the Director of the US National Security Agency General Paul Nakasone said:

This year, we celebrate the 75th anniversary of the formal partnership between the UK GCHQ and the US National Security Agency (NSA).

This alliance defines how we share communication, translation, analysis, and code breaking information, and has helped protect our countries and allies for decades. The amazing women and men at our two agencies use their skills and diversity to make a difference.

Our alliance began before World War II and when it was formalized in 1946, built on a history of strong shared values, including respect for privacy and the rule of law. It grew stronger as Canada, New Zealand, and Australia joined in the years that followed. Together, we are greater than the sum of our parts.

The modern digital world is constantly evolving. Threats don’t respect international borders. Global partnerships are key to our security and economic prosperity – and none more so than the one between our two countries.

For 75 years, this extraordinary partnership has enabled us to evolve and learn from each other. It helps us equip our leaders with the information they need. And it ultimately makes the UK and US safer. We celebrate those 75 years and we look forward to the future together.

For more information, visit a Brief History of the UKUSA agreement