The earliest military application of a balloon is often credited to Zhuge Liang, a well-known war strategist in dynastic China. That was in the 3rd century, when he used kerosene-doused cloth to propel a sky lantern that alerted allies in neighboring cities of a looming attack.

In the almost two thousand years since, balloon technology advanced and was used increasingly for reconnaissance missions during wars in the 19th and early 20th centuries, particularly during the Cold War. But the advent of satellites and drones rendered spy balloons mostly obsolete.

Until recently, it seems.

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On Wednesday, a mysterious white orb was spotted floating above Billings, Montana, and U.S. security officials deemed it almost certainly to be a Chinese military surveillance balloon. The sighting sent politicians on high alert: House Speaker Kevin McCarthy called it a “brazen disregard for U.S. sovereignty” and the Pentagon scrambled fighter jets to deal with it. However, even though the balloon was hovering over sensitive sites, including a field housing U.S. nuclear missiles, the Biden administration ultimately decided not to shoot it down, as officials advised that it doesn’t pose a threat for now but its debris might.

“We have no intention to violate other countries’ sovereignty and airspace,” Mao Ning, a spokesperson for China’s foreign ministry said at a briefing on Friday. “We are gathering and verifying the facts. We hope the relevant parties will handle the matter in a cool-headed way.”

Larry Mayer–The Billings Gazette/APA high altitude balloon floats over Billings, Mont., on Wednesday, Feb. 1, 2023. The U.S. is tracking a suspected Chinese surveillance balloon that has been spotted over U.S. airspace for a couple days, but the Pentagon decided not to shoot it down.

How unusual are spy balloons?

This isn’t the first time in the past year that a balloon from China has been spotted by foreign security officials.

After the sighting this week, the U.S. Department of Defense said in a statement: “Instances of this kind of balloon activity have been observed previously over the past several years.”

Last February, authorities in Taiwan said they discovered weather balloons deployed by the Chinese People’s Liberation Army floating above the self-governing island that China claims as its territory. While some speculated the balloons could be used for surveillance, officials in Taipei accepted that they were meant for meteorological purposes only.

China has been developing new balloon surveillance technology for years, but it’s not the only country to do so.

Last May, Politico reported that the Pentagon spent around $3.8 million on balloon projects over the past two years and planned to spend more than $27 million on the inflatable tech in fiscal year 2023. The balloons, according to the report, will collect data and transmit information to aircraft and may eventually be used to scan for hypersonic weapons developed by China and Russia.

Why use balloons when satellites exist?

China has an extensive satellite network. In a Nov. 2022 report, the Defense Department said China’s intelligence, surveillance, and reconnaissance-capable (ISR) satellite fleet had more than 260 systems, second only to the U.S., as of the end of 2021. A senior defense official noted on Thursday that, for China, the balloon flying over Montana “has limited additive value from an intelligence collection perspective.”

Yet even with satellite technology surpassing some abilities of balloons, James Char, a research fellow with the China Programme at the S. Rajaratnam School of International Studies in Singapore, tells TIME that spy balloons have some operational advantages. For example, balloons can weather extreme conditions, he says, and are less expensive to deploy and operate compared to satellites. Chinese Academy of Science scholars found in 2020 that, despite harsh environments at more than 68,000 feet above ground, “the high-altitude balloon has long endurance time, which can achieve sustained and wider coverage for regional observation and detection.”

“It is harder to be spotted by radar as well, given the fact that they’re simpler in terms of technology,” Char adds. U.S. officials admitted the balloon flying over North America this week was first spotted by civilians on a plane.



High-altitude balloons can also be “trucks for any number of platforms, whether it be communication and data link nodes, ISR, tracking air and missile threats — and without the predictable orbits of satellites,” Tom Karako, senior fellow for the International Security Program and director of the Missile Defense Project at the Center for Strategic and International Studies, told Politico.

And though the technology is old, says Bec Shrimpton, director at the Australian Strategic Policy Institute, balloons can complement surveillance technology in orbit, while they can be built and deployed at a fraction of the cost. According to a 2020 analysis in defense publication Armada International, the development, launch, operation, and insurance of a single satellite can cost up to $300 million.

Another potential edge for balloons, Shrimpton tells TIME, is how unlikely defense officials may have been prepared for it to be used, especially by China. “It’s probably better because it’s unexpected,” she says. “It’s not that we haven’t seen this before, but we are expecting far more from Chinese surveillance efforts.”

If it’s caught, what’s the point?

“It is bold, in that it was always likely to be detected, it was always likely to be seen,” says Shrimpton. That’s what military experts like her find most notable about the balloon, especially given the timing of its emergence—before Secretary of State Antony Blinken’s scheduled trip to Beijing and just after the U.S. reinvigorated its military alliance with the Philippines.

“I think it’s another demonstration of the Chinese military’s adherence to operations below the threshold of war, that’s number one,” says Char. “Clearly for reasons that are known to everyone,” he adds, “the U.S. and the Chinese don’t want to escalate matters above.”

“It is a threat, no doubt,” Char says. “But how serious is it? I think it’s pretty clear: if it’s serious enough, I’m sure something more drastic would have been done by the U.S. establishment.”