The Sea Shepherd boat "Ady Gil" has been sunk by Japanese whalers in Antarctica.
While Sea Shepherd has in fact sunk some whaling ships that were operating illegally in the past, they have strived to keep their operations legal, which means that this is something of an escalation.
Both sides, however, have taken care to avoid loss of (human) life.
The Ady Gil held the record for fastest circumnavigation of the earth. I had a chance to visit the boat and talk to one of the crew while I was in Auckland late last October. It was quite the little boat.