A specialty in counterterrorism.
Robert H Schultz, Jr has a good article on Special Operations Forces. Though they specialize in fighting terrorism, they were never used in that role until after 9/11. (*)
This seems to relate to President Clinton’s idea for “black ninjas” to jump out of helicopters and attack Al Qaeda. (†) It’s easy to mock Clinton’s fascination with ninjas, but the basic idea of covert operations proved itself with devastating effectiveness in Afghanistan.