On Monday, four heavily armed U.S. Air Force F-16 fighters from Misawa air base in northern Japan flew many hundreds of miles to the South China Sea south of Taiwan and buzzed the U.S. Navy aircraft carrier USS Theodore Roosevelt.

The impressive sortie was part of a powerful American response to China’s month-long maritime occupation of a resource-rich reef inside the Philippines’ exclusive economic zone.

American and Philippine ships and planes surged into the South China Sea as a warning to the roughly 220 Chinese militia boats anchored off Whitsun Reef, 200 miles west of the Philippines. The U.S. State Department made it clear—the use of force was on the table.

Beijing blinked—and withdrew its boats. “China realized that its continued presence was simply going to strengthen the resistance,” said Jerry Hendrix, a retired U.S. Navy officer and author of To Provide and Maintain a Navy.

But the American deployments belied the fragility of U.S. air power in the western Pacific. The four F-16s, each packing six air-to-air missiles, were a credible aerial force. But those fighters’ home base is really, really far away from Taiwan and the South China Sea.

It’s possible the F-16s staged from Kadena air base in Japan’s Okinawa prefecture, just 500 miles from the southern tip of Taiwan. It’s also possible the F-16s flew the entire 1,800 miles from Misawa to the Theodore Roosevelt carrier strike group.

In any event, dragging those four fighters to the South China Sea’s hot zone required four Air Force KC-135 tankers, each of which had its radio transponder on and thus was visible on public plane-tracking websites.

One tanker per fighter. After all, an armed F-16 normally can fly no farther than 400 miles without mid-air refuelling.

Leaving aside the two squadrons of F-15s with the 18th Wing at Kadena, the two F-16 units belonging to the 35th Fighter Wing at Misawa are some of the closest USAF forces to Taiwan and the South China Sea.

If the 13th and 14th Fighter Squadrons need a tanker per F-16 to play any meaningful role in fighting around Taiwan, imagine how many tankers a much larger American force would require.

The Chinese People’s Liberation Army Air Force quickly can mobilize hundreds of modern fighters for an attack on Taiwan.

If the U.S. Air Force deployed an equal number of fighters to its bases in the western Pacific—Kadena and Misawa, among them—the service might also have to deploy every tanker in its inventory that isn’t in deep maintenance or busy with crew training. Hundreds in all.

The U.S. military has more, and more modern, warplanes than the PLA does. But the Chinese military has a geographic advantage. Beijing maintains scores of major bases just a few hundred miles from Taiwan.

The United States, by contrast, counts on just a handful of bases—and none is closer than 500 miles from the likeliest Chinese landing zone in southern Taiwan.

That’s one reason that Air Force officials reportedly aren’t assuming the service’s F-35 stealth fighters will play a major role in a war over Taiwan. It’s also a reason the Navy is committed to its thousand-foot supercarriers such as Roosevelt, as well as assault ships such as Makin Island with their contingents of U.S. Marine Corps F-35s.

The carriers can sail directly into the South China Sea and launch waves of fighters. Yes, they’d be vulnerable to attack by Chinese rockets, bombers and submarines. But at least they’d be in the fight.