"We’re the dark matter. We’re the force that orders the universe but can’t be seen."

The president has also given JSOC the rare authority to select individuals for its kill list — and then to kill, rather than capture, them. Critics charge that this individual man-hunting mission amounts to assassination, a practice prohibited by U.S. law. JSOC’s list is not usually coordinated with the CIA, which maintains a similar, but shorter roster of names.

Created in 1980 but reinvented in recent years, JSOC has grown from 1,800 troops prior to 9/11 to as many as 25,000, a number that fluctuates according to its mission. It has its own intelligence division, its own drones and reconnaissance planes, even its own dedicated satellites. It also has its own cyberwarriors, who, on Sept. 11, 2008, shut down every jihadist Web site they knew.

Obscurity has been one of the unit’s hallmarks. When JSOC officers are working in civilian government agencies or U.S. embassies abroad, which they do often, they dispense with uniforms, unlike their other military comrades. In combat, they wear no name or rank identifiers. They have hidden behind various nicknames: the Secret Army of Northern Virginia, Task Force Green, Task Force 11, Task Force 121. JSOC leaders almost never speak in public. They have no unclassified Web site.

Despite the secrecy, JSOC is not permitted to carry out covert action like the CIA. Covert action, in which the U.S. role is to be kept hidden, requires a presidential finding and congressional notification. Many national security officials, however, say JSOC’s operations are so similar to the CIA’s that they amount to covert action. The unit takes its orders directly from the president or the secretary of defense and is managed and overseen by a military-only chain of command.