Defence Intelligence in the context of "MI5"

The Government of the United Kingdom maintains several intelligence agencies that deal with secret intelligence. These agencies are responsible for collecting, analysing and exploiting foreign and domestic intelligence, providing military intelligence, performing espionage and counter-espionage. Their intelligence assessments contribute to the conduct of the foreign relations of the United Kingdom, maintaining the national security of the United Kingdom, military planning, public safety, and law enforcement in the United Kingdom. The four main agencies are the Secret Intelligence Service (SIS or MI6), the Security Service (MI5), the Government Communications Headquarters (GCHQ) and Defence Intelligence (DI). The agencies are organised under three government departments, the Foreign Office, the Home Office and the Ministry of Defence.

Although the history of the organisations dates back to the 19th century or earlier, the British intelligence system as we know it today – with components for domestic, foreign, military, and communications intelligence – did not emerge until the years immediately preceding World War I. The decryption of the Zimmermann Telegram in 1917 was described as the most significant intelligence triumph for Britain during World War I, and one of the earliest occasions on which a piece of signals intelligence influenced world events. During the Second World War and afterwards, many observers regarded Ultra signals intelligence as immensely valuable to the Allies of World War II. In 1962, during the Cuban Missile Crisis, GCHQ interceptions of Soviet ship positions were sent directly to the White House. Intelligence cooperation in the post-war period between the United Kingdom and the United States became the cornerstone of Western intelligence gathering and the "Special Relationship" between the United Kingdom and the United States.

The Defence Intelligence Fusion Centre (DIFC) is based at RAF Wyton in Cambridgeshire. Largely created from the staff of the National Imagery Exploitation Centre (formerly known as the Joint Air Reconnaissance Intelligence Centre (JARIC)) and then known for several years as the Defence Geospatial Intelligence Fusion Centre, it can trace its history back to clandestine reconnaissance operations at the beginning of the Second World War by Sidney Cotton on behalf of MI6 and then MI4, and the formation of the Allied Central Interpretation Unit at RAF Medmenham (sister to Bletchley Park).

Today, DIFC's role has grown beyond just imagery intelligence. Part of the Joint Forces Intelligence Group (JFIG) within Defence Intelligence, DIFC's primary role is to support Defence planning, current operations and the intelligence assessment process. DIFC still provides specialist imagery intelligence, but also conducts multi-disciplinary intelligence fusion for the armed forces and other UK Government partners. The integrated multi-disciplinary Task Groups at DIFC use data and reporting from various sources (including satellite imagery), together with other advanced technologies, to provide critical information and over-watch to tactical, operational and strategic decision makers.

The Joint Intelligence Committee (JIC) is an interagency deliberative body of the United Kingdom responsible for intelligence assessment, coordination, and oversight of the Secret Intelligence Service, Security Service, GCHQ, and Defence Intelligence. The JIC is supported by the Joint Intelligence Organisation under the Cabinet Office.