WASHINGTON — The top military commander overseeing North American airspace said Monday that some previous incursions by Chinese spy balloons during the Trump administration were not detected in real time, and the Pentagon learned of them only later.
“I will tell you that we did not detect those threats, and that’s a domain awareness gap,” said Gen. Glen D. VanHerck, the commander of the Pentagon’s Northern Command.
One explanation, multiple U.S. officials said, is that some previous incursions were initially classified as “unidentified aerial phenomena,” Pentagon speak for U.F.O.s. As the Pentagon and intelligence agencies stepped up efforts over the past two years to find explanations for many of those incidents, officials reclassified some events as Chinese spy balloons.
It is not clear when the Pentagon determined the incidents involved Chinese spying. When the determination was made, officials kept the information secret to avoid letting China know their surveillance efforts were uncovered, the officials said.
In 2021, the intelligence agencies announced an intensified effort to collect more and better data on unexplained incidents near military bases and exercises. While part of a long-term push, those efforts have dramatically increased the percentage of unexplained incidents the Pentagon and intelligence agencies have been able to identify.
Jake Sullivan, the White House’s national security adviser, on Monday credited improved surveillance under the Biden administration with detecting the balloon that passed over the United States last week.
“We enhanced our capacity to be able to detect things that the Trump administration was unable to detect,” said Mr. Sullivan, speaking at an event hosted by the U.S. Global Leadership Coalition.
American officials, who like others in this article spoke on condition of anonymity to discuss sensitive deliberations, have identified at least one other previous incursion during the Biden administration. It is not clear when that incident happened.
John F. Kirby, a National Security Council spokesman, said on Monday that Chinese spy balloons passed over the United States on at least three occasions during the Trump administration.
“From every indication that we have, that was for brief periods of time — nothing at all like what we saw last week in terms of duration,” said Mr. Kirby, referring to the balloon that spent much of last week traversing the country before the United States shot it down.
The Chinese Spy Balloon Showdown
The discovery of a Chinese surveillance balloon floating over the United States has added to the rising tensions between the two superpowers.
Senior Trump administration officials said they were never briefed about incursions by Chinese spy balloons while they were in office. Mr. Trump, on his social media site Truth Social, called the claims of intrusions during his administration “fake disinformation,” and his last director of national intelligence, John Ratcliffe, has also denied it.
A Biden administration official said on Sunday that intelligence officials could offer briefings on China’s balloon surveillance program — which has sent airborne machines over five continents — to key former officials from the Trump administration.
General VanHerck said U.S. intelligence had figured out that some of the unexplained incidents were in fact spy balloons based on “additional means of collection.”
Neither General VanHerck nor Mr. Kirby described how they gathered additional information to determine which of the unexplained incidents involved surveillance balloons.
Balloons account for many of the unexplained incidents the Navy and other military services have tracked in recent years. The previous incidents, like other unexplained events, were handed over to a Pentagon task force charged with investigating U.F.O.s and other aerial phenomena.
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One U.S. official said previous incursions occurred mainly in coastal locations. Multiple kinds of spy balloons have been detected around the world in recent years, the official said. Some were small and fast; others — like last week’s intruder — were bigger and slower moving
The earlier Chinese balloons remained secret because intelligence officials typically do not want adversaries to know their surveillance efforts have been discovered.
The intelligence community issued its first public report on unknown incidents in 2021, but that document failed to offer explanations for all but one of the 144 incidents it looked at.
After that report, the Pentagon and intelligence agencies began to intensify efforts to attribute and explain more incidents. Last year they participated in an open hearing with the House Intelligence Committee, and the Biden administration offered a closed-door briefing to Congress on Chinese surveillance efforts in August, according to a White House spokeswoman.
A follow-up report on the unexplained incidents was delivered to Congress last month and looked at 366 additional reports. While 171 remained unexplained, the report labeled 163 of them as balloons.
Although there has been speculation by the public and lawmakers that some of the unexplained incidents reported by military pilots and recorded by Navy and Air Force sensors could be signs of extraterrestrial activity, U.S. officials working on the issues have said they believe they are surveillance activity or airborne trash.
U.S. officials believe that, in addition to the balloon surveillance, China has used quadcopter drones to spy on the U.S. military. A classified report sent to Congress last month said at least two incidents of surveillance by a foreign power may have involved advanced technology poorly understood by the United States.
While that report did not attribute those incidents to a specific country, two American officials said it is likely those incidents involved Chinese efforts to spy on military installations.
It is not yet clear what the balloon that transited the United States last week was surveilling. But American officials believe previous incidents of Chinese surveillance involved efforts to learn more about pilot training and how the United States coordinates military weaponry to amplify its combat effects.
American officials said they are continuing to try to recover parts of the balloon that was shot down on Saturday, once it had moved over the Atlantic Ocean.
Mr. Kirby, the National Security Council spokesman, said that finding debris and examining it will take some time. “They have recovered some remnants off the surface of the sea,” he said, but he added that weather conditions “did not permit much undersea surveillance of the debris field.”
American officials, Mr. Kirby said, have determined that the balloon was maneuverable. “It is true that this balloon had the ability to maneuver itself,” he said. “So it had propellers. It had a rudder, if you will, to change direction.” He said that the jet stream provided the rest of the balloon’s propulsion.
State Department officials said Monday that they would still try to maintain dialogue with senior Chinese officials even as the two nations assess the fallout from the incursion last week and the diplomatic confrontation over it. They said officials in Washington and Beijing have not begun talks to reschedule the trip to China that Antony J. Blinken, the U.S. secretary of state, canceled on Friday during the public uproar. He had been expected to meet with President Xi Jinping of China.
Ned Price, the State Department spokesman, said officials would determine later “when it’s appropriate to potentially look to travel to the P.R.C. to have the type of discussion that we think is incumbent for our countries to have” — referring to the People’s Republic of China.
Ryan Hass, a former U.S. diplomat and White House official who is a China scholar at the Brookings Institution, said leaders in the two nations would likely adopt a practical approach to managing the relationship despite tense recent episodes.
“The news cycle will move on, and the same challenges in the relationship will remain,” he said. “Both leaders recognize the need to manage risk through direct, hard-nosed diplomacy.”
Mr. Kirby said Mr. Blinken had been headed to China to begin restoring communications between the two governments — on climate and on military issues — that had been severed by the Chinese in the wake of former Speaker Nancy Pelosi’s visit to Taiwan last year. President Biden and Mr. Xi had agreed at a meeting in Bali, Indonesia, in November that the two governments should restart climate discussions.
But the balloon incident has put efforts to restore those communications on hold, Mr. Kirby said, adding that Mr. Blinken’s meeting was meant “to work through some of those difficulties and find a way to to get the relationship on a better footing.”
“Clearly this incident hasn’t helped that process,” he said.
Michael D. Shear contributed reporting.