A look at the US Marine Corps MV-22 Osprey aircraft

The United States is building up its military operations in the Horn of Africa to combat Islamist groups in the region.

Frank Gardner visited the base in Djibouti from where the Americans mount covert missions into Somalia and Yemen.

He looked at a key tool in the armoury of the United States Marine Corps - the MV-22 Osprey - a tilt-rotor aircraft which flies like a plane but can land and take off like a helicopter.