The Twenty Committee (named with a pun: XX = Double Cross) was one of the most remarkable intelligence achievements in history. From 1940 onward, MI5 systematically identified and apprehended every German agent sent to or already operating in Britain. Each was given a choice: work as a double agent or face execution.
The turned agents, given colorful codenames like GARBO, TRICYCLE, ZIGZAG, and BRUTUS, fed a carefully orchestrated mix of truth and fiction back to German intelligence. Juan Pujol García (GARBO), a Spaniard who volunteered his services, was so convincing that the Germans awarded him the Iron Cross while the British gave him an MBE—making him one of the few people decorated by both sides.
The system was so successful that the Abwehr (German intelligence) never realized their entire British network was compromised. The Double Cross agents played crucial roles in every major deception operation, including Operations Mincemeat and Fortitude.