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.