Japanese anxiety about China’s military muscle reveals itself in a fascinating set of numbers.

In a briefing at the headquarters of Japan’s self-defence forces in Naha, Okinawa’s capital, there are few opening formalities. Instead, a series of stark ratios flash across the screen. They offer a raw appraisal of how Japanese policymakers see the power imbalance in North Asia. On the number of ballistic missiles, the ratio is 2300 to zero; on fighter aircraft, 5:1. And on the number of navy and air force bases, China enjoys a 29:1 advantage over its neighbour.