The Rainbow Warrior was the Green Peace flagship (40 metres and 418 tonnes). It was used all over the world to protest about environmental and humanitarian issues.
On july 10th 1985, it was bombed by French Secret Service Officers, killing a photographer, Fernando Pereria.
On december 14th 1987, the boat was towed from Auckland to the Cavalli Islands, and was sunk to be an artificial reef.
This colourfull wreck lies on a sandy floor, maximum depth is 26m (high tide).
More info on WikiPedia: http://en.wikipedia.org/wiki/Rainbow_Warrior