A US guided-missile destroyer that was adrift in the South China Sea without power last month is a sign that America is taxing its reserve capacity as its operation against Iran drags on, according to an analyst. “This is an extremely unusual occurrence and a variety of equipment and process failures would have to have taken place,” said Brad Martin, a former US Navy captain who is now a senior policy researcher at Washington-based think tank the Rand Corporation. “Failures such as this are a...