A desperate band of Ukrainian fighters and more than 1,000 terrified civilians have been holed up beneath a sprawling factory complex for more than seven weeks—the last defenders of the besieged city of Mariupol. Facing an unrelenting barrage of bunker-busting bombs from the air and missile strikes from the sea, the holdouts were surrounded by Russian troops and in dire need of food, ammunition and medical supplies. “I always say that as long as we are here, Mariupol remains under control of Ukraine,” Captain Svyatoslav Palamar, leader of the controversial Azov Regiment, told the BBC from its stronghold under the ruins of the Azovstal steel plant. “We’re surrounded; they’re bombing us with everything they can.” The 24-kilometre maze of tunnels and workshops forms an intricate netwo...