The three-tier vocabulary used to describe human in the loop weapons is an analytical gloss rather than a legal standard. No binding instrument defines the three phrases. The nearest thing to an authoritative source is US Department of Defense Directive 3000.09, which defines three categories of weapon system without using the loop language at all, and it is the Congressional Research Service that maps the familiar phrases onto them. Anyone drafting a requirement, a legal review or a marketing claim should know which of those two documents they are quoting.
The distinction has direct consequences for procurement, and a separate and unresolved one for international law. This guide sets out the definitions as published, then the positions of states and of humanitarian organisations, attributed to each.
What DoD Directive 3000.09 actually defines
The directive, updated in January 2023, is the current US policy on autonomy in weapon systems. It defines an autonomous weapon system as one that, once activated, can select and engage targets without further intervention by a human operator. It defines a semi-autonomous weapon system as one that only engages individual targets or specific target groups that have been selected by a human operator, a category that includes so-called fire-and-forget guided weapons. It defines a human-supervised autonomous weapon system as one in which operators are able to monitor and halt an engagement.
Across all three, the directive requires that systems be designed to allow commanders and operators to exercise appropriate levels of human judgment over the use of force. That phrase, not the loop vocabulary, is the operative US policy standard.
The Congressional Research Service's primer on US policy on lethal autonomous weapon systems supplies the translation: semi-autonomous corresponds to "human in the loop", human-supervised to "human on the loop", and fully autonomous to "human out of the loop". It is a useful shorthand and it is a secondary source. Cite it as such.
Why the loop vocabulary breaks down in practice
The three tiers describe an engagement, not a system. The same airframe can be operated in different modes, and the mode determines which tier applies. This is documented most directly in the literature on loitering munitions, where research published through the AutoNorms project examines systems that can be flown with an operator selecting each target or with target signatures loaded before launch. The companion guide on what a loitering munition definition rests on covers that case in more detail.
Two further ambiguities recur. Supervision is not the same as control: an operator watching a video feed with a two-second window to intervene is "on the loop" in name. And selection is not the same as engagement: a system may autonomously identify candidate objects while a person authorises each one, or a person may designate an area while the system chooses within it. These are different arrangements that the shorthand does not separate.
The published position of the ICRC
The International Committee of the Red Cross set out its position in May 2021 and submitted it to the chair of the Convention on Certain Conventional Weapons Group of Governmental Experts in June of that year. The ICRC recommends that states adopt new legally binding rules, structured in three parts: an express prohibition on unpredictable autonomous weapon systems, meaning those whose effects cannot be sufficiently understood, predicted and explained; a prohibition on autonomous weapon systems designed or used to apply force against persons; and strict regulation of all others.
In October 2023 the UN Secretary-General and the President of the ICRC issued a joint call, published by the UN, urging states to conclude a legally binding instrument on autonomous weapon systems by 2026, setting prohibitions and restrictions including the retention of human control over decisions to use force.
Where states disagree
The Group of Governmental Experts under the CCW endorsed eleven guiding principles by consensus, affirmed at the 2019 Meeting of High Contracting Parties. Those principles state that international humanitarian law continues to apply fully to such systems and that human responsibility for decisions on the use of force must be retained. They do not define autonomy, do not define meaningful human control, and do not prohibit anything.
In December 2023 the UN General Assembly adopted resolution 78/241 on lethal autonomous weapons systems. Human Rights Watch reported the vote as 152 in favour, four against and eleven abstentions, with the resolution requesting the Secretary-General to seek and report the views of states and other stakeholders. The United States voted in favour and, in its published explanation of vote lodged with the UN Office for Disarmament Affairs, stated its view that the time is not right to begin negotiating a legally binding instrument.
That is the shape of the disagreement. A broad majority of states support continued international discussion. A group of states, including several major producers and users of the relevant technology, holds that existing international humanitarian law is sufficient and that national review processes rather than a new treaty are the correct mechanism. Humanitarian organisations, led by the ICRC, hold that new binding rules are required. This site does not take a position between them; it records what each has published.
What a buyer can ask instead
Because the vocabulary is unsettled, requirement documents that specify a tier tend to be unenforceable. Questions about the engagement sequence are more useful. Which function is automated: detection, classification, target selection, or the application of force? Can the system be operated in a mode where no person selects the specific object engaged, and can that mode be disabled and the setting audited? What is the intervention window in seconds, and what happens on loss of link? Is there a log that records who authorised what, and is it exportable? Those questions produce answers a legal reviewer can use; the autonomy due-diligence checklist sets out a fuller version.
None of this is a capability judgement. The index grades companies only on published evidence of deployment, using the four published grades, and the method for testing a supplier's claims is set out in the verification guide, with the thirteen companies that have documented operational use listed separately.
Limits of this reading
The definitions above are US and international-organisation sources. Other states operate their own doctrinal vocabulary, and several have published national commentaries on the CCW guiding principles that differ in emphasis. This guide does not survey them all, and the absence of a national position here is not evidence that none exists.
The debate is live. Positions summarised here are those published at the dates given and may have moved. Nothing in this guide describes what any particular product does, and the index does not connect any product to a named strike, operation or casualty event, for the reasons set out in the no-attribution policy.
Frequently asked questions
What is the difference between human in the loop and human on the loop?
In the loop describes a system where a person selects each target before force is applied. On the loop describes a system that operates autonomously while a person monitors it and can halt an engagement. The phrases are analytical shorthand, not legal definitions.
Does DoD Directive 3000.09 ban autonomous weapons?
No. It sets policy for their design, review and use, defining autonomous, semi-autonomous and human-supervised autonomous weapon systems, and requiring that all of them allow commanders and operators to exercise appropriate levels of human judgment over the use of force.
What has the ICRC recommended on autonomous weapons?
The ICRC recommends new legally binding rules: prohibiting autonomous weapon systems whose effects cannot be sufficiently understood, predicted and explained; prohibiting those designed or used to apply force against persons; and strictly regulating all remaining types.
Sources
- US Department of Defense, Directive 3000.09, Autonomy in Weapon Systems (updated January 2023)
- Congressional Research Service, Defense Primer: U.S. Policy on Lethal Autonomous Weapon Systems (IF11150)
- ICRC, Autonomous weapons: The ICRC recommends adopting new rules, May 2021
- United Nations, Joint call by the UN Secretary-General and the President of the ICRC on autonomous weapon systems, 5 October 2023
- United States, Explanation of vote on General Assembly Resolution 78/241, UN Office for Disarmament Affairs documents library/78-241-US-EN.pdf)
- Human Rights Watch, Killer Robots: UN Vote Should Spur Action on Treaty, January 2024
- ICRC, Commentary on the Guiding Principles of the CCW GGE, UNODA documents
- AutoNorms, Loitering Munitions and Unpredictability: Autonomy in Weapon Systems and Challenges to Human Control, 2023
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