Written by Julian E. Barnes, Helene Cooper and Edward Wong

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 VanHerck, 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,” which is Pentagon-speak for UFOs. 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.

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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 that 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 Sullivan, speaking at an event hosted by the U.S. Global Leadership Coalition.

U.S. 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 Kirby, a National Security Council spokesperson, said 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 Kirby, referring to the balloon that spent much of last week traversing the country before the United States shot it down off the coast of South Carolina.

Senior Trump administration officials said they were never briefed about incursions by Chinese spy balloons while they were in office. Former President Donald 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 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.

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 VanHerck nor 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 that 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 UFOs and other aerial phenomena.

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 — such as 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 that 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 spokesperson.

A follow-up report on the unexplained incidents was delivered to Congress last month and looked at 366 additional reports. Although 171 remained unexplained, the report labeled 163 of them as balloons.

It is not yet clear what the balloon that transited the United States last week was surveilling. But U.S. 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.

U.S. officials said they are continuing to try to recover parts of the balloon that was shot down Saturday, once it had moved over the Atlantic Ocean.

Kirby 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.”

U.S. officials, 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 the jet stream provided the rest of the balloon’s propulsion.

State Department officials said Monday 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 U.S. Secretary of State Antony Blinken canceled Friday during the public uproar. He had been expected to meet with Chinese President Xi Jinping.

This article originally appeared in The New York Times.