I don't have campaign, and it says you can get this in a ranked playlist, so i went on squad battle-it was 1 flag CTF on sandtrap. I lasered 3 guys in a warthog, got the triple kill, and the warthog was destroyed, yet it didn't unlock. I'm just curious as to why it didn't unlock.
http://www.bungie.net/Online/Halo3UserContentDetails.aspx?h3f ileid=118885268