YANGGU, South Korea — Amid the smell of jet fuel and the roar of helicopter engines, U.S. and South Korean forces Thursday carried out an elaborate night air assault exercise that drilled both sides in the methods of shuttling infantry to battle under cover of darkness.

The exercise in the remote reaches of northeastern Gangwon Province saw U.S. helicopters ferry nearly 500 South Korean combat troops and 11 vehicles from a South Korean army installation here in Yanggu to a landing zone near Inje, about 12½ miles east, under mock combat conditions.

The night airlift capability the Americans can provide is beneficial for South Korean forces, said Col. Jung Kang-ho, commanding officer of the South Korean army’s 32nd Infantry Regiment.

“Night air assault is sudden attack” in the dark, he said, and therefore can give South Korean forces the advantage of surprise over an enemy force, he said.

His infantry as well as South Korean helicopters joined forces with about 350 troops of the U.S. Army’s 2nd Combat Aviation Brigade, and 21 of its Black Hawk, Chinook and Apache helicopters, along with other 2nd Infantry Division supporting units, all part of a U.S.-South Korean force called Task Force Wild Card.

Thursday’s night air assault capped about two weeks of task force rehearsals.

Under cool, clear skies and with no moonlight, infantrymen of Jung’s regiment took up concealed positions behind a treeline beside an airstrip here and waited while a line of Black Hawk and Chinook helicopters appeared on the horizon, touched down and lined up one behind the other down the length of the hard-surface runway.

Eventually, a few stars appeared in the sky. Parked in the darkness, the helicopters were murky, barely visible silhouettes.

Later, the flight line came alive with the sudden whirring of machinery and the smell of hot jet fuel as the pilots started their engines. Engine exhaust cast a warm layer of air that lingered at the edges of the runway.

Then, at a signal from their leaders in this complex and tightly orchestrated exercise, the troops dashed single file for the open Black Hawk bays and pulled themselves aboard. Waiting crew chiefs with small flashlights got them seat-belted and safely in place.

The helicopters made return trips until all troops and equipment had been deposited on the landing zone.

“Main thing we keep our eye on is the safety of the soldiers coming on to the helicopter,” said Spc. Weston Fenner, 26, of Abrams, Wis., a Black Hawk crew chief with Company A, 2nd Battalion (Assault), 2nd Aviation Regiment.

“To make sure they don’t walk anywhere near the tail or anywhere the blades may be low. And also to assist them with their seat belts and their weapons. (Reminding them to) keep ’em pointed down, and that way it shoots through the floor and not through any crucial component of the helicopter and not through any person.”

On Thursday night, Fenner was part of a Company A aircrew whose call sign was “Mustang 1” and consisted of Chief Warrant Officer 2 Paul Crandall, 28, of Boise, Idaho; Chief Warrant Officer 2 Steven Jordan, 33, of Enterprise, Ala.; and Spc. Ronald Melton, 31, of Campbellsville, Ky., also a crew chief.

For pilots, a key aim in an airlift is getting the troops to the destination on schedule, the pilots said.

“Put the troops [in] on time, plus or minus 30 seconds,” said Crandall.

And if they see their speed will get them to the landing zone too soon or late, they need to immediately adjust speed so they arrive on time, Jordan said.

South Korean army Capt. Choi Sang-hwan of the 32nd Infantry Regiment’s 1st Company, 1st Battalion said his men too had several things they had to get right in an air assault.

“One minute before [landing], we must check our weapons, and also get off and go in right direction,” taking up positions in an already assigned sector of the landing zone, he said.