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Special Branch is a label customarily used to identify units responsible for matters of national security and intelligence in British and Commonwealth police forces, as well as in Ireland and the Royal Thai Police. A Special Branch unit acquires and develops intelligence, usually of a political or sensitive nature, and conducts investigations to protect the State from perceived threats of subversion, particularly terrorism and other extremist political activity.

The first Special Branch historically recorded, or Special Irish Branch, as it was then known, was a unit of London's Metropolitan Police formed in March 1883 to combat the Irish Republican Brotherhood. The name became Special Branch as the unit's remit widened to include more than just IRA-related counterespionage.

Most state police forces and the federal police had a Special Branch. They were tasked mainly with monitoring the Communist Party of Australia and related political groups regarded as extremist or subversive. They also focused on German and Japanese activity during World War II.

The Security and Intelligence Branch, also known as Special Branch, is the main domestic intelligence and security service in the Commonwealth of the Bahamas. It is mandated to perform intelligence operations inside the Bahamas to ensure the safety of Bahamian citizens and foreigners. The branch is also mandated to perform background checks on persons who have been recruited for jobs such as police officers and defence force officers and to check persons up for promotions. The Director of the Security Intelligence Branch holds the title "Assistant Commissioner".

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