The American commando raids this month against terrorist operatives in Libya and Somalia underscore the spreading extremist threat in Africa, and a renewed urgency to choke off insurgent cells before they can grow, according to counterterrorism specialists. Teams from the brigade here have already helped train forces in Kenya and Tanzania, which are battling fighters from the Shabab militant group in Somalia.

President Obama, at a news conference three days after the commando raids, said Africa was one of the places “that you’re seeing some of these groups gather.”

“And we’re going to have to continue to go after them,” he added.

For that reason, it is no surprise that the military’s Africa Command is the test case for this new Army program of regionally aligned brigades that will eventually extend to all of the Pentagon’s commands worldwide, including in Europe and Latin America next year. These forces will be told in advance that their deployments will focus on parts of the world that do not have Army troops assigned to them now — creating a system in which officers and enlisted personnel would develop regional expertise.

Gen. Ray Odierno, the Army chief of staff, said in an interview that the goal was to field an Army that could be “engaged regionally in all the combatant commands to help them shape their theaters, set their theaters, in order to sustain and execute our national security strategy.”

Even as soldiers prepare for tasks as far-ranging as combat casualty care in Chad or radio training in Mauritania, in a recent visit here they were also conducting target practice in their M1A2 battle tanks on a sprawling firing range, to keep their skills sharp for a future land war against an unforeseen foe. Chad and Mauritania are both combating Al Qaeda in the Islamic Maghreb, an offshoot of the main terrorist group.