AP Photo

The sinking of the South Korean corvette Cheonan in March 2010 reignited global concerns over the proliferation of submarine technology. Although the total number of submarines in service worldwide has declined since the end of the Cold War, largely because of the disappearance of the Soviet navy and a reduction in U.S. forces, the number of countries operating relatively advanced submarines has increased. The People’s Liberation Army Navy (PLAN) in particular has expanded the size and sophistication of its undersea armada. At the same time, capabilities for fighting submarines have atrophied. Altogether, these trends suggest an alarming degree of uncertainty in the relationships among major powers and...