Photos by Jared Soares | The Roanoke Times

Ray Stull and his son Tristan, 5, watch a helicopter land Friday near the Army Reserve fields in Roanoke. The helicopters are part of the 20th Special Operations Squadron stationed in Florida.

You just might hear it before you see it.

And from a distance, the prop noise of the MH-53M Pave Low IV resembles that of other helicopters that occasionally buzz above the Roanoke Valley.

Once it comes closer, though, there's no mistaking the sight or sound of a Pave Low for Lifeguard 10.

With its gray shell, its sloped front windows and its nose-mounted refueling probe, the thing looks like an 88-foot-long Teflon dragonfly.

Through June 5, three of these Sikorsky-built behemoths will periodically cruise over Southwest Virginia, but they do not signal an enemy invasion.

They're part of the U.S. Air Force's 20th Special Operations Squadron within the 1st Special Operations Wing. Members of the 20th SOS, also called the Green Hornets, will be operating out of Roanoke Regional Airport for the next week as they run training exercises.

"We're stationed down at Hulburt Field, at Fort Walton Beach, Florida, right around the Gulf of Mexico," Lt. Col. Gene Becker said. "Periodically throughout the year, we'll go to different places in the country and get training around the mountains. Flying in the mountains is much more challenging than flying down at sea level."

The region has terrain that, according to Maj. Brian Roberts, resembles that of "Afghanistan [or] Columbia. It could be any area around the world that's mountainous."

Becker said the six-man crews will, among other exercises, use their vehicles' terrain-following and terrain-avoidance radar to practice flying in dense fog. Typical training can last from three to six hours and could cover several hundred miles.

"Sometimes it can be four or five hundred miles," he said. "Sometimes we don't go that far from home at all and we just stay working at a couple of landing zones.

"We all initially trained on this aircraft out in Albuquerque, New Mexico, where there are even higher mountains and it's more challenging," he added. "We've got a very good foundation for mountain flying.

"The mountains here in Virginia offer a great opportunity."

The MH-53 was first deployed in 1981 and is primarily used for infiltration, exfiltration and resupply missions.

A public affairs officer for the Air Force said that later this year the MH-53 will be decommissioned and will be replaced by other aircraft, largely the CV-22 Osprey, a tiltrotor aircraft.

Online producer Jordan Fifer contributed to this report.