Following similar agreements with Australia and the Philippines, Japan is initiating formal talks to help Indonesia bolster its naval monitoring of critical sea lanes.

Indonesia sits at the confluence of the world’s busiest sea lanes. Its coastline stretches nearly 55,000km (34,000 miles) and its waters encompass the Malacca and Lombok straits, chokepoints through which trillions of US dollars in global trade pass annually. Yet for years the nation’s navy has lacked the subsurface awareness to monitor, let alone counter, what moves beneath the waves. Japan intends to change that. Tokyo confirmed on June 5 that the two countries had agreed to begin formal talks...