DONETSK REGION, Ukraine — The two helicopters flew low and loud in eastern Ukraine, thwop-thwopping over tilled black soil. They skimmed small lakes glinting in the early-morning light. They glided across tributaries in the rolling hills that knot the region, cloaking themselves from lurking Russian fighter jets.

The mission on Tuesday was straightforward: Head toward an enemy position in Bakhmut and shower the Russians with rocket fire, flying at treetop level or even just a few feet off the ground.

Pilots and crews of the 18th Tactical Aviation Brigade, one of four aviation brigades in the Ukrainian army, have defied the odds of survival against the Russians’ superior technology and numbers. Helicopters were involved in close-up fights earlier in the war, which led to some losses. But now, as Ukrainian troops inch forward in their counteroffensive in the east, the aircraft have been tapped to act something like winged artillery, lobbing their rockets along a parabolic arc.

The fire can help pin down enemy troops or stop their advance, crews said.

The flights are risky because Ukraine does not have helicopters or crews to spare, and Russian fighter jets are ghosts in the region’s skies — often seeing the choppers without being seen, crews said. Despite the danger, their work is essential to keep pressure on the enemy, said Yevhen Kulbida, the unit’s 43-year old deputy brigade commander. Perhaps just as important, the missions serve as a thundering deliverance for the Ukrainian troops they fly over.

“They understand that they’re not alone,” Kulbida said.

The brigade’s work is part of a larger eastern Ukrainian operation against Russian forces to retake ground in the area of Bakhmut, scene of some of the war’s fiercest combat. Crews said they were involved in recent missions to support infantry and hit enemy positions in Andriivka, a strategic village south of Bakhmut. Ukrainian officials said they captured the village and another nearby, which would allow forces to pressure Russian supply lines. The claims were disputed by Moscow, and fighting is ongoing there.

Commanders order up helicopter fire missions on specific targets identified in the field. On Tuesday, the target was a Russian position in a tree line in Bakhmut, and soldiers readied two Soviet-era Mi-8 helicopters. The unguided S-8 rockets they carry have a standard 10 percent chance of striking their targets, but the experienced crews have raised that percentage to between 50 and 60 percent, a pilot said.

Tuesday’s mission was a success, the crews said, as they awaited a damage assessment from surveillance drones.

The work begins when a target is identified. Only then can senior leaders get started on the math problem before them. Given the distances and technology, the crews must fire their weapons at the right place and right time, while flying at speeds up to 124 miles an hour.

Dmytro, a 30-year-old flight engineer on the lead helicopter, explained how that unfolds in the air, providing only his first name in accordance with Ukrainian military regulations.

The crews are offered possible routes, he said, often through the low-slung hills of the Donetsk region that mask their presence from electronic warfare and antiaircraft fire. They fly low on approach to avoid radar detection, about 30 feet off the ground, but over fields they drop to scarecrow level — roaring at roughly six feet.

Once within range, less than four miles from a target, the pilot points the nose up at the angle needed for the rockets to fly true. Part of Dmytro’s job is to release the weapons.

He counts the steep climb: “5, 10, 15, 20, shoot.” Flares eject from the rear to confuse any heat-seeking missiles heading their way. The helicopters then turn sharply and head back.

The morning run was captured by The Washington Post through a camera affixed to Dmytro’s airframe. Within moments of landing, crews buzzed around the two helicopters, pumping fuel into their tanks and hand-loading rockets back into their pods to ready them for the next mission.

These kinds of missions have become routine, Dmytro said. His service since 2014 has included 250 combat missions, he said, including daring runs that began following the full-scale Russian invasion last year. He has crashed three times, he said, and his aircraft has been ablaze and pockmarked with machine gun fire. At one point, he helped bring ammunition to the besieged Azov steel plant in Mariupol.

“The first days were the brightest, and after that, everything became the same,” he said. But the missions offer a critical lifeline for Ukrainian infantry, he said, by hitting Russians with hellfire. The sorties can rake a hectare’s worth of land, he said.

Yet the Mi-8 helicopters, which went into service in the 1960s, are perhaps better suited for museums than combat flights, Kulbida said. They do not offer missile-detection warnings. The unit needs more missiles and newer aircraft, but the focus of Western aviation support to Ukraine has been on American-made F-16s, rather than the less visible helicopters.

“We are often forgotten,” Kulbida said.

Yevhen, a 33-year-old pilot who commanded the lead aircraft for the day, offered some potential solutions to the glaring shortfalls between Russian and Ukrainian aircraft. Helicopters like the U.S.-made Apache are too complicated, he said, but the United States could provide mothballed Cobra gunships, which were retired in 2020. The ability to launch guided missiles would help change the battlefield dynamic, Yevhen said.

The daily missions vastly increased the experience of the crews, with Yevhen totaling 110 combat missions.

But the voracious need for pilots has drawn greener operators.

The second helicopter was commanded by a chipper 53-year-old pilot named Valerii. His total combat missions so far: 16. The rocket firing was jarring at first, he said, but he has grown accustomed to emptying his pods in the blink of an eye.

Valerii has longer experience in civilian cargo flights and humanitarian missions, he said, including aid deliveries in the Democratic Republic of Congo and Sudan and firefighting in Indonesia.

The contrast is significant, he said, but hauling deadlier cargo has given him a similar sense of purpose. And his work has contributed more than fire support, he said.

“Our friends from the infantry have sent us the radio intercepts of the Russians, where you can hear the fear and panic,” he said. “When they hear the humming coming, they do not have time to run away and hide.”