Some of the unmanned aircraft are bound for Somalia, the collapsed state whose border lies just 10 miles to the southeast. Most of the armed drones, however, veer north across the Gulf of Aden to Yemen, another unstable country where they are being used in an increasingly deadly war with an al-Qaeda franchise that has targeted the United States.

Camp Lemonnier, a sun-baked Third World outpost established by the French Foreign Legion, began as a temporary staging ground for U.S. Marines looking for a foothold in the region a decade ago. Over the past two years, the U.S. military has clandestinely transformed it into the busiest Predator drone base outside the Afghan war zone, a model for fighting a new generation of terrorist groups.

The Obama administration has gone to extraordinary lengths to conceal the legal and operational details of its targeted-killing program. Behind closed doors, painstaking debates precede each decision to place an individual in the cross hairs of the United States’ perpetual war against al-Qaeda and its allies.