The two Mi-8 helicopters tore across enemy territory early on the morning of March 21, startling the Russian soldiers below. Inside were Ukrainian Special Forces fighters carrying crates of Stinger and Javelin missiles, as well as a satellite internet system. They were flying barely 20 feet above ground into the hottest combat zone in the war.
Ukraine’s top generals had conceived the flights as a daring, possibly doomed, mission. A band of Ukrainian soldiers, running low on ammunition and largely without any communications, was holed up in a sprawling steel factory in the besieged city of Mariupol. The soldiers were surrounded by a massive Russian force and on the verge of annihilation.
The plan called for the Mi-8s to land at the factory, swap their cargo for wounded soldiers, and fly back to central Ukraine. Most everyone understood that the city and its defenders were lost. But the weapons would allow the soldiers to frustrate the Russian forces for a few weeks more, blunting the onslaught faced by Ukrainian troops elsewhere on the southern and eastern fronts and giving them time to prepare for a new Russian offensive there.
“It was so important to the guys, who were fully encircled, to know that we had not abandoned them, that we would fly to them, risking our lives to take their wounded and bring them ammunition and medicine,” said a military intelligence officer with the call sign Flint, who was on the first flight and described the operation to The New York Times, along with three others involved. “This was our main goal.”
As the two Mi-8s drew closer, they banked hard over the Sea of Azov, flying just above the water’s surface to avoid Russian radar. Then it appeared, the Azovstal Iron and Steel Works, the last bastion of the Ukrainian defenders. In a video from the flight, Azovstal looms like a besieged industrial fortress, bathed in early morning sunlight.
Beyond it was Mariupol, a city reduced in less than four weeks to a smoldering shell. Corpses littered the streets, while the living, those who remained, were mostly below ground, hungry and scared, emerging from basements only to scrounge for water and food.
“It was a sad sight,” said Flint, who was on the lead helicopter. “It was already mostly in ruins.”
For the Kremlin, Mariupol was a prize.
Barely had President Vladimir V. Putin of Russia given the order to invade Ukraine, on Feb. 24, when Russian soldiers began pouring over the border in tanks and armored vehicles, rolling toward the city, a strategic port on the Sea of Azov. Missiles streaked through the pre-dawn darkness, slamming into apartment buildings and wounding the first civilians of the war.
That morning, the general director of Azovstal, an industrial behemoth with more than 11,000 workers, convened his board. The director, Enver Tskitishvili, went on a war footing, deciding to power down the blast furnaces and cease operations for the first time since World War II.
Then the board made a decision that would shape the battle for eastern Ukraine.
Deep beneath the steel plant were 36 bomb shelters, a legacy of the Cold War. The shelters, some more than 20 feet underground, had enough food to feed thousands of people for several weeks. Believing the fighting would not last long, Mr. Tskitishvili and the other executives saw the plant as a sanctuary and invited employees to come there with their families.