Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 153. Command Responsibility for Failure to Prevent, Punish or Report War Crimes
The UK Military Manual (1952) provides:
In some cases military commanders may be responsible for war crimes committed by subordinate members of the armed forces or other persons subject to their control. Thus, for example, when troops commit, or assist in the commission of, massacres and atrocities against the civilian inhabitants of occupied territory, or against prisoners of war, the responsibility may rest not only with the actual perpetrator but also with the commander.
The commander is also responsible, if he has actual knowledge or should have knowledge, through reports received by him or through other means, that troops or other persons subject to his control are about to commit or have committed a war crime and if he fails to use the means at his disposal to ensure compliance with the law of war. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 631.
The UK LOAC Manual (2004) states:
16.36. Military commanders are responsible for preventing violations of the law (including the law of armed conflict) and for taking the necessary disciplinary action. A commander will be criminally responsible if he participates in the commission of a war crime himself …, particularly if he orders its commission. However, he also becomes criminally responsible if he “knew or, owing to the circumstances at the time, should have known” that war crimes were being or were about to be committed and failed “to take all necessary and reasonable measures within his or her power to prevent or repress their commission or to submit the matter to the competent authority for investigation and prosecution”.
16.36.1. The concept of command responsibility was first enunciated in the case of General Yamashita. In that case, General Yamashita was held to have failed to exercise “effective control” of his troops who were carrying out widespread atrocities in the Philippines. The Tribunal held that the nature of the crimes themselves provided prima facie evidence of knowledge and laid down a test that was reflected in the text of the Manual of Military Law Part III of 1958. According to that test, a commander was considered responsible if “he has actual knowledge or should have knowledge, through reports received by him or through other means”.
16.36.2. The Statute of the International Criminal Tribunal for the Former Yugoslavia dealt with command responsibility as follows:
the fact that any of the acts … was committed by a subordinate does not relieve his superior of criminal responsibility if he knew or had reason to know that the subordinate was about to commit such acts or had done so and the superior failed to take the necessary and reasonable measures to prevent such acts or to punish the perpetrators thereof.
16.36.3. The Statute of the International Criminal Court deals with command responsibility as follows:
(i) That military commander or person either knew or, owing to the circumstances at the time, should have known that the forces were committing or about to commit such crimes; and
(ii) That military commander or person failed to take all necessary and reasonable measures within his or her power to prevent or suppress their commission or to submit the matter to the competent authorities for investigation and prosecution.
(b) With respect to superior and subordinate relationships not described in paragraph (a), a superior shall be criminally responsible for crimes … committed by subordinates under his or her effective authority and control, as a result of his or her failure to exercise control properly over such subordinates, where:
(i) The superior either knew, or consciously disregarded information which clearly indicated, that the subordinates were committing or about to commit such crimes;
(ii) The crimes concerned activities that were within the effective responsibility and control of the superior; and
(iii) The superior failed to take all necessary and reasonable measures within his or her power to prevent or repress their commission or to submit the matter to the competent authorities for investigation and prosecution.
16.36.3. Despite the various formulations of the test, there is general agreement on the nature of command and the degree of knowledge required.
16.36.5. The test of command in this context is one of “effective control” over a subordinate. There need not be proof of command in the sense of formal organisational structures “so long as the fundamental requirement of an effective power to control the subordinate, in the sense of preventing or punishing criminal conduct is satisfied”.
16.36.6. Similarly, it is now accepted that an element of knowledge has to be proved, as command responsibility is not a form of strict liability. Actual knowledge is clearly sufficient, but it is also sufficient if a commander “had reason to know”. This has been described as “where he had in his possession information of a nature, which at the least, would put him on notice of the risk of such offences by indicating the need for additional investigation in order to ascertain whether such crimes were committed or were about to be committed by his subordinates”. It follows that possession of the means of knowledge may be regarded, in appropriate circumstances, as being the same as knowledge itself.
Responsibility of civilian authorities
16.37. Civilian superiors will also be liable for the acts of their subordinates in the same way as military commanders, though the difference in the command relationship means that a court is likely to require evidence of actual knowledge or a conscious disregard of information which would have enabled him to know.
Responsibility of states
16.38. Parties to a conflict are obliged to instruct military commanders to prevent breaches of the law of armed conflict and ensure that their subordinates know of their obligations under that law. This provision is based on the principle that an effective disciplinary system to prevent breaches is the best way of ensuring compliance with the law of armed conflict. But failure to do so does not of itself give rise to criminal responsibility.
16.38.1. Heads of state and their ministers are not immune from prosecution and punishment for war crimes. Their liability is governed by the same principles as those governing the responsibility of civilian authorities. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 16.36–16.38.1.
The UK ICC Act (2001), as amended in 2009, states:
Responsibility of commanders and other superiors
(1) This section applies in relation to—
(a) offences under this Part [i.e. genocide, crimes against humanity and war crimes], and
(b) offences ancillary to such offences.
(2) A military commander, or a person effectively acting as a military commander, is responsible for offences committed by forces under his effective command and control, or (as the case may be) his effective authority and control, as a result of his failure to exercise control properly over such forces where—
(a) he either knew, or owing to the circumstances at the time, should have known that the forces were committing or about to commit such offences, and
(b) he failed to take all necessary and reasonable measures within his power to prevent or repress their commission or to submit the matter to the competent authorities for investigation and prosecution.
(3) With respect to superior and subordinate relationships not described in subsection (2), a superior is responsible for offences committed by subordinates under his effective authority and control, as a result of his failure to exercise control properly over such subordinates where—
(a) he either knew, or consciously disregarded information which clearly indicated, that the subordinates were committing or about to commit such offences,
(b) the offences concerned activities that were within his effective responsibility and control, and
(c) he failed to take all necessary and reasonable measures within his power to prevent or repress their commission or to submit the matter to the competent authorities for investigation and prosecution.
(4) A person responsible under this section for an offence is regarded as aiding, abetting, counselling or procuring the commission of the offence.
(5) In interpreting and applying the provisions of this section (which corresponds to article 28 [of the 1998 ICC Statute]) the court shall take into account any relevant judgment or decision of the ICC.
Account may also be taken of any other relevant international jurisprudence.
(6) Nothing in this section shall be read as restricting or excluding—
(a) any liability of the commander or superior apart from this section, or
(b) the liability of persons other than the commander or superior. 
UK, ICC Act, 2001, as amended in 1 September 2009, Section 65.
In the Rauer case in 1946, the British Military Court at Wuppertal found that none of the accused, among which were Major Rauer and other commanding officers, could be tried for having given an order to kill POWs for lack of evidence. However, it tried the accused for being guilty of “being concerned in the killing of the prisoners”. 
United Kingdom, Military Court at Wuppertal, Rauer case, Judgment, 18 February 1946.
Upon signature of the 1977 Additional Protocol I, the United Kingdom stated: “The word ‘feasible’ means that which is practicable or practically possible, taking into account all circumstances at the time including those relevant to the success of military operations.” 
United Kingdom, Declarations made upon signature of the 1977 Additional Protocol I, 12 December 1977, § b.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom stated that it understood the term “feasible” as used in the Protocol to mean “that which is practicable or practically possible, taking into account all circumstances ruling at the time, including humanitarian and military considerations”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § b.