This rather serious report should be of interest to LW. It argues that autonomous robotic weapons which can kill a human without an explicit command from a human operator ("Human-Out-Of-The-Loop" weapons) should be banned, at an international level.
(http://www.hrw.org/reports/2012/11/19/losing-humanity-0)
Modern naval mines probably qualify as 'robotic' in some sense.
I'm not sure what a heat-seeking missile is; a human decided to fire it, but after that it's autonomous. How is that different in principle from a robot which is activated by a human and is autonomous afterwards?
And a bullet is out of human control once you've fired it. Where do you draw the line?