With code names like Eager Pawn and Indigo Spade, such programs typically operate with even less transparency and Congressional oversight than traditional covert actions by the C.I.A.
At first, the news from Yemen on May 25 sounded like a modest victory in the campaign against terrorists: an airstrike had hit a group suspected of being operatives for Al Qaeda in the remote desert of Marib Province, birthplace of the legendary queen of Sheba.
But the strike, it turned out, had also killed the province’s deputy governor, a respected local leader who Yemeni officials said had been trying to talk Qaeda members into giving up their fight. Yemen’s president, Ali Abdullah Saleh, accepted responsibility for the death and paid blood money to the offended tribes. The strike, though, was not the work of Mr. Saleh’s decrepit Soviet-era air force. It was a secret mission by the United States military, according to American officials, at least the fourth such assault on Al Qaeda in the arid mountains and deserts of Yemen since December.