If nothing else, this series on access denial shows that anti-access strategy comes in many varieties. Vietnam too is pursuing such a strategy, founded on a squadron of six Kilo-class submarines Russia is building for the Vietnam People’s Navy under a contract inked in 2009. In August the Vietnamese press reported that the first boat has been launched, and that all six will be delivered by 2016. The elusive Kilos should make a lethal access-denial force. While China’s People’s Liberation Army Navy operates Kilos itself, it has conspicuously neglected antisubmarine warfare hardware and techniques. It seems South China Sea waters will remain opaque to Chinese commanders for the foreseeable future despite the PLA Navy’s overwhelming superiority over the Vietnam People’s Navy.

First consider the politics of access denial, as we did with Iran and North Korea. Vietnam and China, like North and South Korea, are contiguous powers with vital interests at stake in the same waters. Vital interests like territory beget strong passions. Whereas Iran prizes its ability to manage offshore waters and skies more than the United States cares about operating there—and thus commands a political edge—both Hanoi and Beijing are impassioned about their maritime claims in the South China Sea. Both are prepared to wage efforts of serious magnitude and duration,commensurate with their material capacity to carry on the competition. Neither is likely to relent after dispassionately tallying up the costs and hazards of operating in waters its opponent wants to place off-limits. The result: a combustible situation.

Several tactical and operational characteristics of Vietnamese access denial are worth pondering. Its anti-access force, like all such forces, is asymmetric to the adversary it is designed to oppose. But unlike relatively balanced Iranian and North Korean forces, the Vietnamese access-denial contingent is almost purely one-dimensional. Hanoi doubtless chose well if it could select only one platform to execute its strategy. Submarines offer enormous bang for the buck, and they are survivable. Still, this also means that advances in Chinese antisubmarine warfare could nullify Vietnam’s effort to fend off the PLA Navy. Next, Vietnamese access denial could take on an offensive as well as a defensive character. Vietnamese Kilos could, say, loiter unseen off the Chinese naval station at Sanya, on Hainan Island, holding PLA Navy submarines at risk at the delicate moment when they are entering or leaving port—exposing them to enemy action.

Access denial—a strategically defensive posture—could therebytake on an escalatory hue.The inception of a Vietnamese undersea fleet will further crowd the already crowded waterspace of Southeast Asia, complicating efforts to discriminate among friend, foe, and bystander. China operates Kilos; so will Vietnam; even India could conceivably dispatch Kilos to the region. And this leaves aside the different submarine types deployed by Singapore, Malaysia, and other regional seafaring states. The chances for miscalculations and mishaps will only grow as access-denial strategies take shape.

Not long ago, pundit Robert Kaplan pronounced the South China Sea “the future of conflict.” Kaplan may have spoken truer than he knew.