CORRECTION: This story has been corrected to reflect the rank of Maj. Stephen Bomar, spokesman for the Oregon National Guard.

Low-flying Chinook helicopters rattled residents late Thursday night from South Salem to Keizer.

For much of the day after, no one seemed to know who they were or where they came from. They weren't from the Oregon National Guard. They weren't based locally.

The large, twin-engine, tandem-rotor military aircraft, conducting a refueling exercise at Independence State Airport, buzzed over local neighborhoods between 10 p.m. and midnight.

"They literally shook my apartment so hard that pictures fell off the walls," Keizer's Jay Free wrote in a 12:04 a.m. email to the Statesman Journal. "The last one just flew by. Why is this happening? It's worrying me."

"What are they doing flying so low and so late?" a resident posted around midnight on the neighborhood social platform Nextdoor Sumpter in South Salem.

While we don't have those answers, we can now tell you they were special ops helicopters from the U.S. Army's 4th Battalion of the Army's 160th Special Operations Aviation Regiment (SOAR) based at Joint Base Lewis-McChord in Washington.

The regiment is better known as the "Night Stalkers," and its missions include attack, assault and reconnaissance assignments and are usually conducted at night, at high speeds and at low altitudes. They fly the MH-47G Chinook, a special ops variant of the CH-47.

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Wayne Nutsch, the owner of Nutsch Aviation, opened his doors Thursday night to crews from the active duty Army unit so they could stay warm during refueling. His company sells fuel, but they trucked in their own.

He downplayed complaints from area residents about the noise and the hour.

"It could have been the Russians or the Chinese. I'm glad it was the U.S. Army," said Nutsch, a 30-year Army veteran. "People need to know we have a military force that is protecting our country."

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Few received an advance warning

Some residents in Independence learned about the exercise via a Facebook post by Independence Police Department:

"The military will be conducting a refueling exercise. It will begin around 10:00 PM and go through Midnight. Two Army CH-47 Chinook helicopters will be using the Independence Airport for this exercise. There will be two cycles of this operation."

The Oregon Aviation Department was notified a few days in advance. Airport Operations Specialist Don Hankwitz received a heads up from a chief warrant officer with the 4th Battalion, 160th SOAR.

"They were very conscientious about letting us know and giving us the details of what they were doing," Hankwitz said.

His office passed along the information to homeowners and tenants of the air park neighborhood in Independence. No other public notification was made, however.

The state aviation department was not aware of any plans to make low-altitude passes around the Salem-Keizer area.

"They told us they were going to do training refueling cycles at the airport. That's the only information we had," Hankwitz said.

Independence State Airport, the only airport in Polk County, is state-owned and federally funded. Because it's a public use airport, State Airports Manager Matt Maass said his office can't restrict aviation activities.

The helicopters would have been required to follow FAA rules and regulations like any small airplane, he said. They would not have been required to file a flight plan.

David Foster, who lives near Salemtowne in West Salem, also emailed the Statesman Journal and noted how loud the helicopter was and how low it was flying.

"Our main concern was that somebody was in trouble," Foster said.

"We're kind of in a flight path. We hear helicopters go up frequently," he said. "Usually, they’re up much higher. It felt like they were awful close to the ground, which is not normal. I thought somebody might be going down, that something was not right."

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Lewis-McChord base hit by snowstorm

Col. Alan Gronewold, state Army aviation officer for the Oregon National Guard, was quick to confirm Friday morning that the helicopters were not theirs and they were not conducting training out of Independence.

"We do fly there," said Maj. Stephen Bomar, spokesman for the Oregon National Guard, "but normally we let folks know."

A public affairs officer, who didn't provide his name, reached Friday afternoon at Joint Base Lewis-McChord could not confirm helicopters from the 4th Battalion, 160th SOAR conducted the exercise.

"We are in the process of closing down the base because of the incoming snowstorm," he said. "Everybody except mission critical people are getting out of here.

"It's conceivable," he continued. "Our helicopter units fly all over the place within the Pacific Northwest down to California, Utah and elsewhere. I know it's normal operations to stop at airports along the way en route to wherever they're training."

Earlier this week, video emerged of the 160th SOAR conducting a low-flying training exercise in downtown Los Angeles. That one involved an aircraft touching down in the middle of the street and picking up special operators as they rushed out of a building.

Capi Lynn is the Statesman Journal's news columnist. Her column taps into the heart of this community — its people, history, and issues. Contact her at clynn@StatesmanJournal.com or 503-399-6710, or follow her the rest of the week on Twitter @CapiLynn and Facebook @CapiLynnSJ.