The US intelligence community has developed a method to track China’s fleet of surveillance balloons that was only discovered within the last year, six people familiar with the matter tell CNN.
After President Joe Biden took office in 2021, a Chinese spy balloon briefly transited the continental United States, as administration officials have acknowledged. Afterwards, the intelligence community ran some of the balloon’s signals through the US’ intelligence holdings and other data to see where and when they may have popped up in the past.
The findings have allowed the US to develop a consistent technical method for the first time that they have used to track the balloons in near-real time across the globe, the sources said. The existence of this method could further inflame criticism from Republican lawmakers that the administration didn’t act quickly enough to prevent the balloon from entering US airspace last week.
Officials were also able to use the information collected from the earlier balloon alongside other sources to discover that similar surveillance balloons had transited US territory undetected at least three times under the Trump administration. Officials declined to say how the signals were collected, and it is not clear how long it took the intelligence community to develop the new method, which was first used in 2022.
But the new method is important because the balloons are extremely difficult to track without it – they are slow-moving and can fly extremely high, in some cases as high as much as 60 miles up, and can evade the more traditional radars that are oriented toward detecting fast-moving missiles and counterterrorism threats, a lawmaker familiar with the intelligence told CNN.
Officials emphasized that the balloon’s signals were an important key to discovering a tracking method, but not the only piece of the puzzle. One Defense Department official described the process by which the US was able to identify past instances of these so-called high-altitude balloons – what the Pentagon now refers to as HABs – as “piecing together” different clues from different sources of intelligence.
“We were able to go back and look at the historical patterns” of the balloons,” national security adviser Jake Sullivan said this week. “And that led us to come to understand that during the Trump administration, there were multiple instances where the surveillance balloons traversed American airspace and American territory.”
The revelation that the intelligence community only within the last year developed a reliable way to track China’s balloon fleet – which officials now say has flown dozens of missions worldwide – helps explain why Trump administration officials have stridently claimed to have had no knowledge of the three alleged flights over US territory during the former president’s time in office.
Senior Trump administration officials including former Secretary of Defense Mark Esper, former Secretary of State and CIA Director Mike Pompeo, as well as ex- national security adviser John Bolton have all said they were not notified that Chinese balloons entered US airspace under the last administration.
A broader understanding of the Chinese fleet
The tracking method provided an important tool as US officials monitored the latest balloon to transit the continental United States, gathering intelligence on it as it crossed the country before it was ultimately shot down off the coast of South Carolina last Saturday.
“This last week provided the United States with a unique opportunity to learn a lot more about the Chinese surveillance balloon program, all information that will help us to continue to track these kinds of objects,” Pentagon spokesman Brig. Gen. Pat Ryder said on Wednesday.
And it has allowed the US to keep an eye on other Chinese spy balloons around the globe. Another balloon, in South America, recently went down in the ocean to the east of the continent – although at this point, US officials tell CNN, they aren’t entirely sure what happened. Three US officials familiar with the intelligence say that the US still isn’t certain whether some of these balloons are equipped with a self-destruct mechanism.
The US’ ability to track the balloons’ whereabouts has also added to the broader understanding of how large China’s balloon surveillance program actually is.
On Thursday, officials revealed that they believe the spy balloons the US has discovered are part of a large fleet that is conducting surveillance operations globally on behalf of China’s military, the People’s Liberation Army. So far, the US has traced the balloons to 40 countries across five continents, officials said.
A 2022 military intelligence report obtained by CNN said a balloon was tracked near Guam as far back as 2019.
A former government official investigating strange aerial sightings by Navy pilots over recent years – some of which government officials have said have turned out to be balloons – described a meeting several months ago where a defense official “pulled out of his pocket a piece of a Chinese balloon with Chinese writing on it.”
“The point is, it’s not new that there are Chinese balloons,” the former official told CNN.
The US was able to track the latest balloon’s path even before it entered US airspace. The Defense Intelligence Agency warned that the balloon was headed for the US on January 27, one day before it entered the country over Alaska, officials told CNN.
But military and intelligence officials believed the best course of action would be to continue tracking the balloon and collect intelligence on it, as it was not deemed a threat as it crossed over the US and shooting it down would risk civilian lives and reduce the chances of recovering the balloon’s equipment intact.
US officials briefed members of Congress on Thursday that the balloon had the ability to collect so-called “signals intelligence” and transmit data to the mainland of China – but that it appeared to stop transmitting once the US learned about it, limiting how much intelligence it was able to gather on behalf of Beijing, according to sources familiar with the briefing.
The US also understands that China is using the balloons for surveillance based on “high-resolution imagery” taken by reconnaissance planes as they flew past the balloon that flew over the US last week.
“We know the PRC used these balloons for surveillance,” an official said. “High-resolution imagery from U-2 flybys revealed that the high-altitude balloon was capable of conducting signals intelligence collection operations.”
CNN’s Sean Lyngaas contributed to this report