Data on air bases suggest a Chinese invasion of Taiwan may not be imminent

No one save Xi Jinping, China’s president, knows for certain whether he plans to invade Taiwan. The government’s rhetoric, which calls for “peaceful reunification” but does not rule out force, is meticulously vague. But military investments may offer clues about his intentions.

Since Mr Xi became president ten years ago, China’s defence spending after adjusting for military-cost inflation has risen by 39%. But new data on air bases imply that war over Taiwan is just one of numerous Chinese military priorities. Since 2013 China has built fortified shelters for planes in almost every logical area—except those near Taiwan. Unfortunately for Taiwan, America’s efforts to protect its own bases near the island have been lacklustre.

War planners reckon that even amid a conflict, military aircraft spend only one-third of their time flying. While parked, a plane’s stealth and speed count for nought. In some war games simulating a Chinese invasion of Taiwan, 90% of American aircraft losses occur on the ground.

Spreading out planes across bases limits vulnerability. But parked planes can be shielded from attacks that evade air defences only in robust buildings that absorb incoming fire, called hardened aircraft shelters (has). Although has do not offer full protection, they reduce damage and make enemies use extra munitions. And the closer air bases with has are to combat zones, the less time protected planes lose in transit. Thomas Shugart of the Centre for a New American Security, a think-tank, has compiled a record of the sites of Asian airports used by air forces, and the number of shelters and runways at each one.

Overall, China has been improving its preparations for a potential air war. In 2012 Taiwan had 306 has, more than China’s 297. Since then China has built 380 more. America has just 15 has within 1,000km (620 miles) of Taiwan, where the risk of attack is most acute, all of them in Okinawa.

However, the locations of China’s new has should let Taiwan breathe easier. In 2012, 70% of China’s has were within 500km of Taiwan. Of those built later, just 9% are. Most new sites sit along China’s borders and in its populous east and south. Construction of air bases lacking has, which still provide extra runways and can hide planes’ locations, has also clustered in these areas. This makes sense for a modernising air force facing a range of threats—not for one focusing mainly on Taiwan. China’s fastest jets take 90 minutes to fly from Beijing to the Taiwan Strait.

Mr Shugart’s tally may not be complete. China also has bases underground, though such shelters can be vulnerable to bunker-busting bombs and cruise missiles. Moreover, if China plans to rely on missiles rather than planes, it may think it has enough has near Taiwan already. In war games, however, America sometimes makes destroying Chinese air power a top priority.

As for America, failing to protect $100m jets with relatively cheap has, which are especially useful against the cluster munitions that China stockpiles, seems curious. Analysts have long called for new has. But those wanting to pour concrete abroad are up against constituencies that would rather improve bases at home or buy more kit.

America can only guess at China’s plans. Leaving its planes exposed could prove costly if it guesses wrong.■