Ukraine tried to keep secret its stealthy use of sixteen Mi-8 transport helicopters to keep the defenders supplied in the besieged Azovstal steel plant. The plant was located in the Ukrainian port city of Mariupol. The Russians were frustrated by their inability to take the steel plant, which is on the coast. Russia sent in a lot of their best troops to take the plant but were repulsed for three months before the several hundred surviving Ukrainian troops surrendered on May 18th and were registered by the Red Cross according to the Geneva Convention on prisoners of war. Russia had agreed to let the Red Cross register the steel plant prisoners and claimed they had captured 1,700 troops. That is more than three times as many as the Red Cross has registered. Ukraine and Russia have both generally observed the Geneva Convention and have even carried out some prisoner exchanges early on. As the number of captured Russians increased much more rapidly than the number of Ukrainian troops captured, Russia lost interest in exchanges or even admitting how many Russian POWs the Ukrainians helped. Russia wanted to limit the number of confirmed Russian dead and captured, even though the Ukrainians published the data and, when Russian prisoners offered telephone numbers of their relatives, the Ukrainians would contact them, sometimes even allowing the Russian prisoner to make the call and confirm that he was all right. Most Russian believed the Ukrainian claims because the Russian government had declared such information a military secret in an effort to conceal the extent of their losses. By May senior Russian officials, most of them retired, openly criticized the government treatment of families seeking information on their sons. Some officials still employed by the government began complaining as well, and then resigned.
Which brings us back to the way Ukraine used Mi-8 helicopters to resupply the steel plant defenders and even bring in some reinforcements. This was done at night, at low altitude. While some helicopters were spotted by the Russians and fired on, only three were brought down. One of these was trying to rescue the crew of a downed helicopter. There were rumors of these missions but no evidence of official confirmation. That changed after a Chinese newspaper published a photo of one of the downed Mi-8s on March 31st. Russia continued to deny it and the Ukrainian government had no comment. Russians would only say that they continued to attack the steel plant and would not reveal their casualties which, according to Ukrainian sources, were substantial. The defenders took advantage of a complex system of tunnels under the plant, which the defenders know more about than the Russian attackers.
In May the Russians agreed to allow the remaining steel plant defenders to surrender, with the wounded receiving medical treatment and the soldiers registered by the Red Cross as POWs. There were apparently still some civilians in the tunnels, helping to care for the wounded and do whatever else was needed. Russia may have counted the captured civilians as combatants. Civilians had good reason to seek shelter in the steel plant because Russian artillery fire on the city had already killed over 10,000 civilians and wounded many more. The Red Cross is having problems getting information from the Russians and the Ukrainians admitted to the Mi-8 resupply missions but not details of the supplies brought in. Much of it was ammunition, as well as medical supplies and food. The Russians had increased their air defense activity around the coastal approaches to the steel plants and more MI-8 missions were aborted because of that. It may be months or years before full details of the steel plant defenders and the Ukrainian helicopter support is known.