The extremely high speeds hypersonic weapons travel at reduce an adversary’s ability to react to them. Suppose two nuclear-armed countries—let’s call them India and Pakistan—have hypersonic weapons and nuclear weapons. Both weapons are located in each country’s capital. A hypersonic missile launched from Pakistan’s capital, Islamabad, will reach the Indian capital of New Delhi in just over six minutes.

Under this scenario, India has just six minutes to decide whether the attack is real, what to do about it, and to do something before the missiles hit. That’s virtually no time at all. India might well choose to launch its own weapons as soon as it detects an incoming attack to prevent them from being destroyed on the ground. But what if the attack is the result of an early warning system malfunction, or was launched by accident? By the time India figures that out, the retaliatory strike —and perhaps a nuke—is already underway. The United States, China, and Russia could all have similar problems with one another.