Rule 155. Defence of Superior Orders
Rule 155. Obeying a superior order does not relieve a subordinate of criminal responsibility if the subordinate knew that the act ordered was unlawful or should have known because of the manifestly unlawful nature of the act ordered.
Summary
State practice establishes this rule as a norm of customary international law with respect to war crimes committed in both international and non-international armed conflicts. This rule is without prejudice to the existence of other defences, such as duress, which are not addressed in this study.
International and non-international armed conflicts
The rule that a superior order is not a defence was set forth in the Charters of the International Military Tribunals at Nuremberg and at Tokyo.[1] 
During the negotiation of Additional Protocol I, the ICRC submitted a draft article which prohibited the defence of superior orders if the person “should have reasonably known that he was committing a grave breach of the Conventions or of the present Protocol”. This proposal was not accepted, although the principle enunciated in the Charters of the International Military Tribunals was not contested.[2]  Reasons for not adopting this draft varied, but States mentioned problems with the limitation of the draft rule to grave breaches, which was too narrow, and the fact that subordinates had a duty of obedience, whereas the draft did not limit liability to acts which were manifestly illegal.[3]  Practice since the Diplomatic Conference leading to the adoption of the Additional Protocols, outlined below, has confirmed the customary nature of the rule that superior orders are not a defence.
The rule that superior orders are not a defence is restated in the Statutes of the International Criminal Court, of the International Criminal Tribunals for the former Yugoslavia and for Rwanda and of the Special Court for Sierra Leone and in UNTAET Regulation No. 2000/15 for East Timor.[4]  Conditions are spelled out in some detail in the Statute of the International Criminal Court: obedience to an order is not a defence when the person knew the order was unlawful or when the order was manifestly unlawful.[5]  The Convention against Torture and the Inter-American Convention on the Forced Disappearance of Persons also state that superior orders cannot be a defence.[6] 
Several military manuals and the legislation of many States provide that a superior order is not a defence if the perpetrator knew or should have known that the act ordered was unlawful.[7]  Other military manuals and national legislation exclude this defence in situations where the act was manifestly unlawful without mentioning a particular mental element.[8]  However, it is safe to conclude that if an act is manifestly unlawful the subordinate should at least have known, if he or she did not actually know, that the act ordered was unlawful. Several judgements in recent cases, some of which concerned non-international armed conflicts, reached essentially the same conclusions.[9]  There is no practice to the contrary in relation to acts that are manifestly unlawful. However, practice that solely refers to the unlawfulness of the act ordered, without the requirement of knowledge of such unlawfulness, is not sufficiently widespread and uniform as to establish a rule of customary international law.
Mitigation of punishment
There is extensive practice to the effect that obeying an order to commit a war crime can be taken into account in mitigation of punishment, if the court determines that justice so requires. This practice includes the Charters of the International Military Tribunals at Nuremberg and at Tokyo, the Statutes of the International Criminal Tribunals for the former Yugoslavia and for Rwanda and of the Special Court for Sierra Leone and UNTAET Regulation No. 2000/15 for East Timor.[10] 
In addition, there is extensive State practice to this effect in military manuals, national legislation and official statements.[11]  Some States, however, exclude mitigation of punishment for violations committed pursuant to manifestly unlawful orders.[12] 
In his report to the UN Security Council on the draft Statute of the International Criminal Tribunal for the former Yugoslavia in 1993, the UN Secretary-General referred to the possibility of mitigating punishment in the case of obedience to superior orders.[13]  A similar point is contained in the final report of the UN Commission of Experts Established pursuant to Security Council Resolution 935 (1994) to examine violations of international humanitarian law committed in Rwanda.[14] 

[1] IMT Charter (Nuremberg), Article 8 (cited in Vol. II, Ch. 43, § 855); IMT Charter (Tokyo), Article 6 (ibid., § 863).
[2] See the practice of the CDDH (ibid., § 856).
[3] See, e.g., the statements of Argentina (ibid., § 974), Canada (ibid., § 977), Israel (ibid., § 984), Mexico (ibid., § 988), Norway (ibid., § 991), Poland (ibid., § 992), Spain (ibid., § 995), Syrian Arab Republic (ibid., § 997), United Kingdom (ibid., § 999), United States (ibid., § 1002), Uruguay (ibid., § 1004) and Yemen (ibid., § 1006).
[4] ICC Statute, Article 33 (ibid., § 860); ICTY Statute, Article 7(4) (ibid., § 869); ICTR Statute, Article 6(4) (ibid., 870); Statute of the Special Court for Sierra Leone, Article 6(4) (ibid., 861); UNTAET Regulation No. 2000/15, Section 21 (ibid., 873).
[5] ICC Statute, Article 33 (ibid., § 860).
[6] Convention against Torture, Article 2 (ibid., § 857); Inter-American Convention on the Forced Disappearance of Persons, Article VIII (ibid., § 858).
[7] See, e.g., the military manuals of Germany (ibid., § 881), South Africa (ibid., § 886), Switzerland (ibid., § 889), United States (ibid., §§ 892–893 and 895) and Yugoslavia (ibid., § 897) and the legislation of Belarus (ibid., § 904), Egypt (ibid., § 910), Ethiopia (ibid., § 913), Germany (ibid., §§ 916–918), Iraq (ibid., § 919), Luxembourg (ibid., § 923), Netherlands (ibid., § 924), Poland (ibid., § 929), Slovenia (ibid., § 931), Switzerland (ibid., § 936), Yemen (ibid., § 940) and Yugoslavia (ibid., § 941).
[8] See, e.g., the military manuals of Cameroon (ibid., § 875), Canada (ibid., §§ 876–877), Dominican Republic (ibid., § 879), Peru (ibid., § 885) and South Africa (ibid., § 887) and the legislation of Albania (ibid., § 898), Brazil (ibid., § 906), France (ibid., § 914), Israel (ibid., § 920), Netherlands (ibid., § 925), Peru (ibid., § 927), Rwanda (ibid., § 930) and Spain (ibid., §§ 932–934).
[9] See, e.g., Argentina, National Court of Appeals, Military Junta case (ibid., § 942); Austria, Supreme Court, Leopold case (ibid., § 944); Belgium, Court-Martial of Brussels, Sergeant W. case (ibid., § 945); Belgium Court of Cassation, V. C. case (ibid., § 946); Belgium, Military Court, Kalid case (ibid., § 947); Bosnia and Herzegovina, Republika Srpska, Modrića Municipal Court, Halilović case (ibid., § 948); Canada, Supreme Court, Finta case (ibid., § 949); Germany, Reichsgericht, Llandovery Castle case (ibid., § 954); Germany, Federal Supreme Court, Subordinate's Responsibility case (ibid., § 955); Israel, District Military Court for the Central Judicial District and Military Court of Appeal, Ofer, Malinki and Others case (ibid., §§ 956–957); Israel, Supreme Court, Eichmann case (ibid., § 958); Italy, Military Tribunal at Verona, Schintlholzer case (ibid., § 959); Italy, Military Tribunal of Rome and Supreme Court of Cassation, Priebke case (ibid., § 960); Netherlands, Special Court in Amsterdam, Zühlke case (ibid., § 961); Nigeria, Supreme Court, Nwaoga case (ibid., § 963); Philippines, Supreme Court, Margen case (ibid., § 964); South Africa, Appeal Division, Werner case (ibid., § 965); United Kingdom, Military Court at Lüneberg, Auschwitz and Belsen case (ibid., § 966); United States, Military Tribunal at Nuremberg, Krupp case (ibid., § 967), Krauch (I.G. Farben Trial) case (ibid., § 968) and Von Leeb case (The High Command Trial) (ibid., § 969); United States, Military Commission in Wiesbaden, Hadamar Sanatorium case (ibid., § 970); United States, Army Board of Review, Griffen case (ibid., § 971); United States, Army Court of Military Appeals, Calley case (ibid., § 972).
[10] IMT Charter (Nuremberg), Article 8 (ibid., § 855); IMT Charter (Tokyo), Article 6 (ibid., 863); ICTY Statute, Article 7(4) (ibid., § 869); ICTR Statute, Article 6(4) (ibid., § 870); Statute of the Special Court for Sierra Leone, Article 6(4) (ibid., § 861); UNTAET Regulation No. 2000/15, Section 21 (ibid., 873).
[11] See, e.g., the military manuals of Canada (ibid., § 876), New Zealand (ibid., § 883), Nigeria (ibid., § 884), Switzerland (ibid., § 889), United Kingdom (ibid., § 890) and United States (ibid., §§ 892–893 and 895), the legislation of Australia (ibid., § 901), Bangladesh (ibid., § 903), Chile (ibid., § 908), Congo (ibid., § 909), Ethiopia (ibid., § 913), France (ibid., §§ 914–915), Germany (ibid., § 916), Niger (ibid., § 926) and Switzerland (ibid., § 936) and the statements of Canada (ibid., § 977), Israel (ibid., § 983) and Poland (ibid., § 992).
[12] See, e.g., the military manuals of Canada (ibid., § 876) and New Zealand (ibid., § 883) and the legislation of Spain (ibid., § 932).
[13] UN Secretary-General, Report pursuant to Paragraph 2 of Security Council Resolution 808 (1993) (ibid., § 1009).
[14] UN Commission of Experts Established pursuant to Security Council Resolution 935 (1994), Final report (ibid., § 1012).