The ferry Estonia left Tallinn on the evening crossing to Stockholm and sank in the Baltic in the early hours, between roughly ten to one and ten to two in the morning. It was 1994. There was a gale running and a heavy beam sea; the ship was carrying 989 people, most of them Swedish and Estonian. The Mayday came shortly after one o'clock and the radio traffic stopped soon after that.
The ships nearest were other night ferries on the same route, Mariella and Silja Europa among them, and they turned and came. Helicopter crews flew out of Finland and Sweden into the dark and the weather and worked until morning. The sea was around ten or eleven degrees, which gives a person very little time. Of those aboard, 137 survived. 852 died.
At ten or eleven degrees a person in the water is fighting cold shock in the first minutes and losing use of their hands well before an hour is out, even in a lifejacket. The crews flying and sailing in that night knew exactly how narrow the margin was, and went anyway.
There's a memorial on the slope below Maarjamäe in Tallinn, a broken line of dark stone, with the names cut into it; Stockholm has its own, in the Galärvarvet churchyard, where the names run along low walls. People still leave flowers at both.