Thailand’s navy has to watch two seas at once. To the east lies the Gulf of Thailand, with its busy shipping lanes, offshore energy interests and long coastal frontier with Cambodia. To the west is the Andaman Sea, a gateway to the Indian Ocean with its own trade routes, chokepoints and strategic pressures. That twin-sea geography has long given the Royal Thai Navy a role larger than its public profile might suggest. It also underpins the navy’s stated goal, laid out in a 2023 white paper, to...