KYIV, Ukraine (AP) — As was his habit before each flight, the veteran Ukrainian army pilot ran a hand along the fuselage of his Mi-8 helicopter, caressing the heavy transporter's metal skin to bring luck to him and his crew.

They would need it. Their destination — a besieged steel mill in the brutalized city of Mariupol — was a death trap. Some other crews didn't make it back alive.

Still, the mission was vital, even desperate. Ukrainian troops were pinned down, their supplies running low, their dead and injured stacking up. Their last-ditch stand at the Azovstal mill was a growing symbol of U...