Japan is building a 21st-century military, but it is running out of 21st-century citizens to staff it.

Surrounded by an increasingly assertive China and a nuclear-armed North Korea while facing deepening military cooperation between Moscow and Pyongyang, Tokyo has shattered decades of pacifist precedent, boosting defense spending to nearly 2% of gross domestic product and shedding several of its self-imposed postwar constraints.

But military power is measured not only in hardware but also in the people available to operate and sustain it.?