An autonomous fighter jet called a Reaper was shot down over Northern Afghanistan last weekend after it went AWOL and attempted to fly outside Afghan airspace.
According to USAFCENT Public Affairs:
The aircraft was flying a combat mission when positive control of the MQ-9 was lost. When the aircraft remained on a course that would depart Afghanistan's airspace, a US Air Force manned aircraft took proactive measures to down the Reaper in a remote area of northern Afghanistan.
So basically a jet with a human driver hunted down the robot-driven jet and killed it.
The Register's Lewis Page comments:
It wasn't clear from the US military announcement whether the erratic death-bot had turned on its masters and was planning an attack on critical US logistics bases located north of the Afghan border, or whether it had sickened of reaping hapless fleshies like corn and was hoping merely to escape. Alternatively the machine assassin may merely have succumbed to boredom or - just possibly - a mundane, non-anthropomorphic technical fault of some kind.
I'm voting for "sickened of reaping hapless fleshies."
via The Register