Department of Defense Directive 3000.09: Autonomy in Weapon Systems, November 21, 2012 [open pdf - 191KB]
From the document: "This Directive: a. Establishes DoD policy and assigns responsibilities for the development and use of autonomous and semi-autonomous functions in weapon systems, including manned and unmanned platforms. b. Establishes guidelines designed to minimize the probability and consequences of failures in autonomous and semi-autonomous weapon systems that could lead to unintended engagements."
DoD Directive 3000.09; DoDD 3000.09