The British Ministry of Defense had an unusual security breach recently when an email containing the promotions of noncommissioned officers, some of whom serve in special missions units, was accidentally distributed across the government.

Among the regular promotions of conventional troops were the names of commandos with the Special Air Service, Special Boat Service, and Special Reconnaissance Regiment, as well as the Special Forces Support Group.

Some of those named serve in an elite, classified outfit known as Special Air Service, E Squadron — or “the Increment.”

A secret unit within a secret world, E Squadron works for the British intelligence services in high-risk operations overseas.