When America goes to war, its soldiers, sailors and pilots typically have long been used to having a spectacular technological edge. Those days are ending fast.

From the South China Sea to Eastern Europe — and even the Korean Peninsula — U.S. commanders are now considering the prospect of war against enemies who may be capable of deploying overwhelming firepower and sophisticated new technology. Confrontations with Russia and China in particular are escalating far faster than predicted — with the realistic prospect either nation could outgun U.S. forces in their immediate neighborhood in the early stages of any conflict.

The Pentagon is increasingly worried about rapid proliferation of Chinese and Russian anti-ship and anti-aircraft missile systems, putting U.S. military planners in an unfamiliar position. The last time U.S. forces went to war without an overwhelming advantage was against Nazi German troops in North Africa in 1943.