In late June, the Thai navy told reporters it had elected to buy three submarines from China. The billion-dollar purchase has yet to be officially finalized, and specifics regarding the decision remain murky. While the deal will move Bangkok one step closer to acquiring a capability it has lacked for more than six decades, it has become caught in a broader debate about Thailand’s perceived drift away from the United States and toward China following a coup last year.

Thailand’s submarine quest is neither new nor surprising. The country has lacked a submarine capability since 1951 and has tried since the 1990s to ink submarine deals with several countries, including Germany and South Korea. Supporters of the submarine purchase contend that the country needs them urgently to help advance Thailand’s important maritime interests and keep pace with its neighbors in a cost-effective way. ...