The British Army's 'Green Slime' and the evolution of secret warfare

Wars & Conflicts · Published 16 October 2026 Swipe more like this →

In short: From a tiny group of officers and their servants in 1914 to a sophisticated combat support arm, the Intelligence Corps has shaped modern espionage. They are the architects of counter-intelligence, the analysts of aerial photography, and the operatives who once parachuted into occupied France.

The Intelligence Corps (Int Corps) was officially established in August 1914, though proposals for its creation began in 1905. In its infancy, the unit was composed exclusively of officers and their servants, with a small initial recruitment of about 50 men from the Army, the Metropolitan Police, and civilian life. To maintain secrecy, the officers' batmen were given a cover story as enlisted men in the 10th (Service) Battalion, The Royal Fusiliers. Despite its small size, the Corps was immediately deployed to France, utilizing tools like aerial photography from the Royal Flying Corps and wireless tapping to gather data.

The Corps' history is marked by periods of expansion and dissolution. It was disbanded in 1929 following the Irish War of Independence, where it had monitored the Irish Republican Army. It was reconstituted on July 19, 1940, under Army Order 112. This era saw the Corps take on high-stakes roles: training operatives for the Special Operations Executive (SOE), founding the Special Air Service (SAS) with Lt Col Peter Clayton, and providing roughly 40 percent of the personnel at Bletchley Park. During WWII, they also managed the debriefing of high-ranking prisoners of war in East Africa and implemented screening commissions to identify civilians who assisted Allied escapees.

Today, the Corps is classified as a combat support 'Arm' rather than a 'Service'—a distinction made official in 1985. Personnel are known by the nickname 'Green Slime' due to their distinctive cypress green berets. The Corps maintains a high proportion of commissioned officers, many of whom rise from the ranks. Modern roles range from operating in East Germany behind the Iron Curtain during the Cold War to supporting various brigades in Northern Ireland and across the UK. Their motto, 'Manui Dat Cognitio Vires,' reminds them that knowledge provides the strength of the arm.

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