Every day, nearly 60 fully loaded very large crude-oil carriers sail between the Persian Gulf and Chinese ports, carrying about half of the oil that powers the world's second-largest economy.
As the vessels enter the South China Sea, they ply waters increasingly controlled by China's growing military, from the missile batteries and airfields at its bases on disputed islands to its stealthy Type 055 destroyers.
But when crossing the Indian Ocean en route to China, joined by others from Africa and Brazil, these tankers lack protection in a naval theater dominated by the U.S.