As Captain Tharamadurai noses his patrol boat between the low-slung banks of mangrove forests towards the Malacca Strait, he has centuries-old problems on his mind: pirates and smugglers.

But for worried governments from Washington to Tokyo the Malaysian marine police officer represents the frontline of defence against a more modern menace: terrorists.

The Malacca Strait, a narrow waterway slicing Indonesia's sprawling Sumatra island from mainland Southeast Asia, is one of the busiest shipping lanes in the world, funnelling 50,000 vessels a year between the biggest economies of the West and the East.