The US base at Camp Lemonier in Djibouti is a key operational asset in a troubled region, with al-Qaeda active in nearby Somalia and Yemen. Some 3,000 US troops, as well as armour, fighters and drones are based there. But the US is also experimenting with a different kind of military mission - soft power through soldiers as aid workers, in an effort to deny militant extremists support among Africa's poor. The BBC World Service's Dan Damon has been given rare access to the US operation.
In a one-room library in the remote Djiboutian town of Ali Sabieh, Capt Courtney Sanders, a US soldier from Mississippi, is teaching children how to read English.
She and her team helped build the library and hold regular conversation classes there.
Capt Sanders' Civil Affairs team is part of a counterinsurgency mission with a difference.
Instead of sending in fighting troops once trouble has started in a poor country, the US is getting its soldiers to work on projects that, it is hoped, will build enough stability and opportunity to encourage the people of East Africa to hold onto peace and not fight over scarce resources.
"Since 9/11, the US government has gone through a profound shift in its philosophy behind how operations are conducted in the Horn of Africa," says Col William Hollingsworth, one of the longest serving members of the Combined Joint Task Force - Horn of Africa, or CJTF-HOA, which is coordinating the humanitarian side of soldiering here.
"The 'bumper sticker' name for this is the 3D process," he says.
Defence, diplomacy and development are the 3 Ds, designed as a virtuous triangle of American power projected overseas.
The base for the CJTF, Camp Lemonier in Djibouti City, houses plenty of conventional military firepower.
In a hanger on the airstrip, there is a Predator drone. Flying overhead, fighter planes, which the Americans say are French.
The US gives no information about how it is using those weapons.
There have been US air strikes on Somali militant group al-Shabab in recent years and a US special operations team was reported to have killed al-Shabab leader Saleh Ali Saleh Nabhan inside Somalia in 2009.
Camp Lemonnier is also the focus of allegations of other anti-terrorism activities by soldiers based there.
The campaign group Reprieve says Djibouti has been used for secret renditions and imprisonment of terrorism suspects from al-Shabab - allegations Washington flatly denies.
Whatever the combat operations out of Camp Lemonnier today, after the killing of 19 US soldiers and the wounding of 70 others in Mogadishu in 1993, there is no appetite for full scale ground operations in Somalia.
Instead, the Pentagon is keen to talk about soldiers in humanitarian and development projects.
Why are soldiers doing what aid workers have traditionally done?
Because they can, says Col Hollingsworth.
"The US military brings a tremendous amount of capability and experience in the kinds of things this new philosophy requires.
"Manpower and budget mean it was inevitable the military would be included in development and diplomacy."
The nomadic herders struggling to survive in the village of Guistir, in the furnace-hot mountains on Djibouti's border with Somalia and Ethiopia, have no hesitation in supporting the CJTF mission.
US soldiers helped to build a clinic in Guistir. Without it, the villagers, who have not seen significant rain in three years and whose animals are either emaciated or long dead, would have to walk dozens of miles to get medical help.
The clinic's nurses also run reading classes for the children; food aid is delivered there.
"What do you think of Americans?" I asked village chief Adil Ali Gedde, a devout Muslim living just a few kilometres from Somalia.
His response would be music to the ears of most US politicians.
"We congratulate the American army and we are very glad to see them here," he says.
Ultimately, though, the chaos in Somalia and the escalation of fighting in Yemen are the really serious problems in the region.
If Yemen continues on its slide to chaos, the militants of al-Qaeda in the Arabian Peninsula known to be based there will be able to recruit and train more easily and increase attacks on the West.
Already, at least two aeroplane bomb plots and the Fort Hood shootings have been blamed on radical US Muslim cleric Anwar al-Awlaki, currently thought to be in hiding in Yemen.
So there are complaints that the US is mounting a confused mission, far too little to deal with the sources of conflict.
A senior officer in the neighbouring French base in Djibouti told me: "The Americans never share any intelligence with us, about Somalia or about Yemen, which is in a civil war."
The Roman Catholic Bishop of Djibouti, Giorgio Bertin, has spent 30 years trying to mediate between clans and warlords in Somalia.
He is also critical of the US mission: "This is not the right policy. It is taking care of someone who is sick without going to the causes of the sickness. With only a humanitarian approach, we will not solve the problems of Somalia. I'm not against the use of force when it is necessary."
The giant US presence has another impact that Djiboutians complain of - in private.
America is paying a lot for the right to use the base and that should give them plenty of leverage over Djibouti's government.
But so far, people say when they are sure they are not being overheard, the Americans appear to have done nothing to deal with the corruption and patronage that blight Djibouti, keeping it from the huge economic potential that goes with its strategic position.
On the road west, that potential is most obvious in the hundreds of overladen trucks grinding their way to Ethiopia.
Since that country's war with Eritrea began more than a decade ago, Ethiopia's only access to the sea is through Djibouti's port.
The port road runs past luxury gated communities and the vast, white presidential palace of Ismail Omar Guelleh, 30 years in power.
Further along the road, the scrap metal shanties and huts made of cardboard and plastic that so many Djiboutians are forced to live in.
It is an ugly contradiction, and so far America's soft power experiment has failed to challenge it.