WASHINGTON — Deploying a little-known National Guard reconnaissance plane in four American cities to monitor protests this spring did not violate rules against the military collecting intelligence on citizens, a Pentagon report has concluded.
But the report by the Air Force inspector general found that National Guard officials failed to obtain prior approval from Defense Secretary Mark T. Esper to use the planes because they mistakenly believed they were not intelligence aircraft, which require high-level signoff.
The inquiry was prompted by lawmakers who expressed concerns to Pentagon officials that the use of the aircraft, RC-26B surveillance planes, in late May and early June may have violated the civil liberties of the mostly peaceful protesters demonstrating against police brutality and systemic racism.
Mr. Esper responded by ordering an investigation, which was conducted by Lt. Gen. Sami D. Said, the Air Force inspector general. The Air Force’s action came after the Pentagon’s top intelligence policy official told Congress that the nation’s military intelligence agencies did not spy on American protesters during the wave of nationwide demonstrations.
The Air Force investigation into the use of the RC-26B aircraft in Washington, Minneapolis, Phoenix and El Dorado Hills, Calif., determined that the planes were used to gather information about crowd size, movements of protesters and cars, threats to buildings and fires, but that they did not monitor individuals.
“There was no personal information collected on these missions,” the report found. “The sensors on the aircraft were not capable of identifying any distinguishing features of people, or other potentially identifying characteristics such as race or gender.”
None of the aircraft flying over the cities carried equipment that could collect information from cellphones or hand-held radios, the report concluded.
Thousands of National Guard troops were used to assist local law enforcement in several cities around the country during the protests. But the Air Force report highlighted how Pentagon policies about the approval and use of the secretive RC-26B aircraft were vague, misunderstood by military planners on the ground and needed to be fixed.
In Phoenix, for instance, National Guard planners working with the local police described how the aircraft could be used “to deter planned/unplanned demonstrations, protests or looting.”
“Properly approved missions can support civilian law enforcement, but there is no scenario in which it is acceptable or permissible to use D.O.D. assets to deter demonstrations and protests, assuming they remain lawful,” the report concluded, referring to the Department of Defense.
“The missions were not used to track individuals, but there was a risk they could have been,” the report said.
The RC-26B, a twin-engine aircraft outfitted for electronic surveillance, is most often used along the southwestern border to monitor illegal immigration and to counter drug smuggling in the Caribbean, as well as in disasters to assess damage and help locate civilians.
But during the protests, the planes conducted the first-of-its-kind missions to support the local law enforcement authorities on the ground.
On the morning of June 2, hours after National Guard helicopters harassed crowds of protesters in Washington, National Guard officials informed their commanders that the West Virginia Air National Guard had sent an RC-26B to help observe the protests with “FMV capabilities” — or full-motion video — according to a message viewed by The New York Times.
According to one military official familiar with the situation, senior National Guard leaders in Washington could watch the footage recorded from the aircraft on their cellphones in real time. This most likely meant that the RC-26B would circle overhead and beam video to the F.B.I. command center near the Chinatown area of Washington.
RC-26B pilots say the plane’s onboard camera is powerful enough to determine the general image of an individual as the three-member crew flies at altitudes of 4,000 to 20,000 feet. But the cameras are not strong enough or sophisticated enough to use for facial recognition or to read license plates on vehicles, they say.
Despite the planes’ extensive surveillance abilities, the Air Force report found that military commanders did not consider the RC-26B an intelligence aircraft, which would require more senior approval for the use of the plane and stricter guidance on the missions.
The use of the planes was not approved by Mr. Esper, an Army veteran who also once served in the District of Columbia National Guard, because officials did not believe that was required. But the report concluded the defense secretary should have had the final word over those types of delicate missions to prevent the military from using its vast arsenal for law enforcement purposes without proper oversight.
In the end, the report concluded, that did not happen, at least in the case of the seven RC-26B flights. “There is no evidence individuals or specific organizations were targeted, followed or identified,” the report said.
The Air Force report did not examine the use of National Guard helicopters to harass protesters by hovering over them, creating a deafening roar and blasting the crowd with rotor wash.