AROUA INTERNATIONAL AIRPORT, proclaimed the sign on the concrete and glass terminal building. The designation was something of a misnomer, because only three or four planes land each week in this sleepy outpost in northern Cameroon, near the Nigerian border, all of them domestic flights. The schedule of the flights tends to be unpredictable. The aging jet that had just flown me to Garoua from Douala, for example, had made an unscheduled stop in N'Djamena, the capital of neighboring Chad, so that a government minister could attend a funeral nearby. As a result, the plane had touched down in Garoua five hours late.

But that wasn't the only unusual thing about this Cameroon Air flight. Inside the cabin I had noticed several young men who were unmistakably U.S. military — close-cropped hair, athletic builds. And as I descended from the plane and set foot on the tarmac into the blast furnace heat, I spotted a curious triumvirate waiting for them: a middle-aged, sunburned white man wearing cargo pants and a green T-shirt, flanked by two U.S. soldiers in camouflage gear.