Counterterrorist

Counter-terrorism (also spelled counterterrorism) (also called anti-terrorism) incorporates the practice, military tactics, techniques, and strategy that government, military, law enforcement, business, and intelligence agencies use to combat or prevent terrorism. Counter-terrorism strategies include attempts to counter financing of terrorism.

If terrorism is part of a broader insurgency, counter-terrorism may employ counter-insurgency measures. The United States Armed Forces use the term foreign internal defense for programs that support other countries in attempts to suppress insurgency, lawlessness, or subversion or to reduce the conditions under which these threats to security may develop.

In response to the escalating terror campaign in Britain carried out by the militant Irish Fenians in the 1880s, the Home Secretary, Sir William Harcourt, established the first counter-terrorism unit ever. The Special Irish Branch was initially formed as a section of the Criminal Investigation Department of the London Metropolitan Police in 1883, to combat Irish republican terrorism through infiltration and subversion.

Harcourt envisioned a permanent unit dedicated to the prevention of politically motivated violence through the use of modern techniques such as undercover infiltration. This pioneering branch was the first to be trained in counter-terrorism techniques.

Its name was changed to Special Branch as it had its remit gradually expanded to incorporate a general role in counterterrorism, combating foreign subversion and infiltrating organized crime. Law enforcement agencies, in Britain and elsewhere, established similar units.

...
Wikipedia