1 The terms “international humanitarian law” and “law of armed conflict” are used interchangeably in this text since they convey precisely the same meaning – albeit with a different semantic emphasis.

2 Geneva Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field; Geneva Convention (II) for the Amelioration of the Condition of Wounded, Sick and Shipwrecked Members of Armed Forces at Sea; Geneva Convention (III) Relative to the Treatment of Prisoners of War; and Geneva Convention (IV) Relative to the Protection of Civilian Persons in Time of War, all of which were adopted on 12 August 1949 and entered into on force 21 October 1950. Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (AP I); and Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of Non-International Armed Conflicts (AP II), both adopted on 8 June 1977 and entered into force on 7 December 1978.

3 ICCPR, 16 December 1966 (entered into force 23 March 1976).

4 International Committee of the Red Cross (ICRC), “Strengthening Legal Protection for Victims of Armed Conflict”, 31st International Conference of the Red Cross and Red Crescent, Geneva, October 2011, p. 4.

5 UN Basic Principles on the Use of Force and Firearms by Law Enforcement Officials, adopted by the 8th United Nations Congress on the Prevention of Crime and the Treatment of Offenders, Havana, Cuba, 27 August–7 September 1990 (BPUFF).

6 There are several LOAC-specific obligations for States to respect and ensure respect of the law based on the Geneva Conventions (including common Article 1) and their Additional Protocols. There are similar obligations in IHRL, including Article 2 of the ICCPR. See ICRC, The Domestic Implementation of Humanitarian Law: A Manual, Geneva, April 2013.

7 See in particular AP I, Art. 87, as elaborated in ICRC, Integrating the Law, Geneva, May 2007, available at: www.icrc.org/eng/resources/documents/publication/p0900.htm (all internet references were accessed in December 2014).

8 ICRC, above note 6, p. 127. For examples of the work of IHL committees, see Cristina Pellandini, “Ensuring national compliance with IHL: The role and impact of national IHL committees” and the accompanying section in this issue.

9 See, for example, Vité, Sylvain, “Typology of Armed Conflicts in International Humanitarian Law: Legal Concepts and Actual Situations”, International Review of the Red Cross, Vol. 91, No. 873, 2009, p. 94CrossRefGoogle Scholar.

10 See Sassòli, Marco, “Taking Armed Groups Seriously: Ways to Improve Their Compliance with International Humanitarian Law”, Journal of International Humanitarian Legal Studies, Vol. 1, 2010, pp. 5–51CrossRefGoogle Scholar.

11 This term was coined by General Charles Krulak in his article “The Strategic Corporal: Leadership in the Three Block War”, Marines Magazine, January 1999.

12 AP I, Art. 87.

13 Ibid., Art. 87(2).

14 Munoz-Rojas, Daniel and Frésard, Jean-Jacques, “The Roots of Behaviour in War: Understanding and Preventing IHL Violations”, International Review of the Red Cross, Vol. 86, No. 853, 2004, p. 194Google Scholar.

15 Ibid., p. 190.

16 Ibid., p. 196.

17 ICRC, above note 7, pp. 17–35.

18 Ibid.

19 See AP I, Art. 36.

20 These principles are reflected in the treaty and customary rules governing the conduct of hostilities in armed conflict, including AP I, Arts 48–58, and Rules 1–21 of Jean-Marie Henckaerts and Louise Doswald-Beck (eds), Customary International Humanitarian Law, Vol. 1: Rules, Cambridge University Press, Cambridge, 2005 (ICRC Customary Law Study).

21 ICRC, Decision-Making Process in Military Combat Operations, Geneva, October 2013, available at: www.icrc.org/eng/resources/documents/publication/p4120.htm.

22 ICRC, above note 7, pp. 17–35.

23 See AP I, Art. 82.

24 Statutes of the International Red Cross and Red Crescent Movement, adopted by the 25th International Conference of the Red Cross at Geneva in October 1986 and amended by the 26th International Conference of the Red Cross and Red Crescent at Geneva in December 1995 and by the 29th International Conference of the Red Cross and Red Crescent at Geneva in June 2006.

25 Nils Melzer, Interpretive Guidance on the Notion of Direct Participation in Hostilities under International Law, ICRC, Geneva, May 2009 (ICRC Interpretive Guidance).

26 See International Criminal Tribunal for the former Yugoslavia, Office of the Prosecutor, Final Report to the Prosecutor by the Committee Established to Review the NATO Bombing Campaign against the Federal Republic of Yugoslavia, 13 June 2000, para. 56; Human Rights Watch, “The Crisis in Kosovo”, Civilian Deaths in the NATO Air Campaign, Vol. 12, No. 1, 2000Google Scholar; Rogers, A. P. V., “Zero-Casualty Warfare”, International Review of the Red Cross, No. 837, March 2000Google Scholar.

27 There were however cases in which altitude became a factor for visual identification. See, for example, the NATO bombing of Djakovica-Decane, in which civilian vehicles forming part of a refugee convoy were mistaken for a military convoy. See Human Rights Watch, above note 26.

28 Ibid.

29 See AP I, Arts 51(5)(b) and 57(2)(b).

30 See Geiss, Robin, “The Principle of Proportionality: ‘Force Protection’ as a Military Advantage”, Israel Law Review, Vol. 45, No. 1, 2012, pp. 71–89CrossRefGoogle Scholar; Michael Schmitt, “Fault Lines in the Law of Attack”, in Essays on Law and War at the Fault Lines, TMC Asser Press, The Hague, 2012, pp. 296–297.

31 Ibid.

32 See Zwanenburg, Martin, “International Humanitarian Law Interoperability in Multinational Operations”, International Review of the Red Cross Vol. 95, No. 891, 2013, pp. 681–705CrossRefGoogle Scholar.

33 Above note 2.

34 See Alan Cole, Phillip Drew, Rob McLaughlin and Dennis Mandsager, Rules of Engagement Handbook, International Institute of Humanitarian Law, Sanremo, November 2009.

35 RoE governing the use of force against objects are beyond the scope of this article.

36 These generic categories of force may be subdivided under several headings: use of force in defence of self and others, mission accomplishment, targeting in armed conflict, operations related to property, etc. See ibid., Annex B.

37 See section “Restraints on the Use of Force against Otherwise Lawful Targets?”, below. Fighters may not be attacked if they are hors de combat. Medical and religious personnel remain protected against attack.

38 See AP I, Arts 48–58.

39 ICRC Interpretive Guidance, above note 25, pp. 32–36.

40 See Dr. Jakob Kellenberger's Foreword to ibid., pp. 4–7.

41 Ibid., pp. 24, 31–32. From this perspective, it is important to note that the RoE term “declared hostile force” must be defined as the fighting forces of a party to the armed conflict, as opposed to its civilian component (which might include its political leadership, civilian employees and others), whether those forces belongs to a State or non-State party. This article uses the term “organized armed group” to represent only the armed wing of a non-State party to an armed conflict.

42 Ibid., p. 35.

43 Ibid., Chapter 2.

44 See, for example, Watkin, Kenneth, “Opportunity Lost: Organized Armed Groups and the ICRC ‘Direct Participation in Hostilities’ Interpretive Guidance”, New York University Journal of International Law and Politics, Vol. 42, No. 3, 2010, pp. 662–664Google Scholar.

45 Corn, Geoff and Jenks, Chris, “The Two Sides of the Combatant Coin”, University of Pennsylvania Journal of International Law, Vol. 33, 2011, p. 338Google Scholar. See also Melzer, Nils, “Keeping the Balance between Military Necessity and Humanity: A Response to Four Critiques of the ICRC's Interpretive Guidance on the Notion of Direct Participation in Hostilities”, New York University Journal of International and Politics, Vol. 42, No. 3, 2010, p. 856Google Scholar: “the ICRC's Interpretive Guidance cannot, and does not purport to, replace the issuing of contextualized rules of engagement or the judgment of the operational commander. Instead, it aims to facilitate the task of those responsible for the planning and conduct of operations by providing useful and coherent concepts and principles based on which the required distinctions and determinations ought to be made.”

46 See the following section, “Conduct-Based RoE”.

47 This is the concept of proportionality in attack contained in AP I.

48 Importantly, these same criteria are applicable to irregular armed forces belonging to a State party to an armed conflict. See ICRC Interpretive Guidance, above note 25, pp. 25, 31.

49 See Schmitt, Michael, “The Interpretive Guidance on the Notion of Direct Participation in Hostilities: A Critical Analysis”, Harvard National Security Journal, Vol. 1, 2010, pp. 21–24Google Scholar. See also K. Watkin, above note 44.

50 M. Schmitt, above note 49, p. 23.

51 N. Melzer, above note 45, p. 852.

52 Report of the Special Rapporteur on Extra-Judicial, Summary or Arbitrary Executions, Philip Alston, UN Doc. A/HRC/14/24/Add.6, 28 May 2010, pp. 20–21.

53 N. Melzer, above note 45, pp. 837–855.

54 See AP I, Art. 50(1), note 2.

55 For a discussion of the meaning of the concepts of hostile act and hostile intent, see A. Cole et al., above note 34, Part II.

56 ICCPR, above note 3, Art. 6.

57 Above note 5.

58 UN Human Rights Committee, ICCPR General Comment 31, “The Nature of the General Obligation Imposed on States Parties to the Covenant”, UN Doc. CCPR/C/21/Rev. 1/Add.13, 29 March 2004, para. 10. For a summary of the contrary position held by the United States, and a critique of that position, see Schaack, Beth Van, “The United States’ Position on the Extraterritorial Application of Human Rights Obligations: Now is the Time for Change”, International Law Studies, Vol. 20, No. 90, 2014Google Scholar.

59 UN Charter, Art. 38. See Terry Gill, Carl Marchand, Hans Boddens Hosang and Paul Ducheine, General Report for the 19th Congress of the International Society for Military Law and the Law of War, Quebec City, 1–4 May 2012, Parts 4, 5, 6. See also Gloria Gaggioli (ed.), Expert Meeting: The Use of Force in Armed Conflicts – Interplay between the Conduct of Hostilities and Law Enforcement Paradigms, Geneva, October 2013, pp. 11–12.

60 This is derived from the fact that the UN Code of Conduct for Law Enforcement Officials, adopted by UNGA Res. 34/169 of 17 December 1979, uses the term “law enforcement officials” to describe “all officers of the law . . . who exercise police powers, especially the powers of arrest or detention”, inclusive of armed forces, in Art. 1(a). The same terminology is employed in the BPUFF, above note 5.

61 International Court of Justice (ICJ), Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 8 July 1996, ICJ Reports 1996, para. 25. See also ICJ, The Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion, 9 July 2004, ICJ Reports 2004, para. 106; and ICJ, Case Concerning Armed Activity on the Territory of the Congo (Democratic Republic of Congo v. Uganda), Judgment, 19 December 2005, ICJ Reports 2005, paras 216–220.

62 ICJ, Nuclear Weapons, above note 61, para. 25.

63 See for example G. Gaggioli, above note 59, pp. 9–12.

64 Ibid., p. 59.

65 ICRC Interpretive Guidance, above note 25, Recommendation IX. See section “Restraints on the Use of Force against Otherwise Lawful Targets?”, below.

66 See BPUFF, above note 5.

67 Ibid. See also G. Gaggioli, above note 59.

68 ICRC Customary Law Study, above note 20, Rule 6. See also AP II, Art. 13(3), note 2.

69 ICRC Interpretive Guidance, above note 25, Recommendation VII.

70 See, for example, William Boothby, Conflict Law: The Influence of New Weapons Technology, Human Rights and Emerging Actors, TMC Asser Press, The Hague, 2013, p. 252.

71 See section “Restraints on the Use of Force against Otherwise Lawful Targets?”, below.

72 See International Criminal Tribunal for the former Yugoslavia, Prosecutor v. Dusko Tadić, Appeals Chamber, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, 2 October 1995, para. 70; and Prosecutor v. Ramush Haradinaj, Trial Chamber, Judgment, 29 November 2012, paras. 392–396, which elaborate on the Tadić intensity and organization requirements.

73 ICRC Interpretive Guidance, above note 25, pp. 58–64.

74 Ibid., Recommendation II.

75 See the LOAC definition of armed conflict found in the documents cited at note 72.

76 See section “Conduct-Based ROE”, above.

77 Subject of course to procedural safeguards. See Pejic, Jelena, ‘Procedural Principles and Safeguards for Internment/Administrative Detention in Armed Conflict and Other Situations of Violence’, International Review of the Red Cross, Vol. 87, No. 858, 2005, pp. 375–391CrossRefGoogle Scholar.

78 As defined by a CCF per the ICRC. See ICRC Interpretive Guidance, above note 25, pp. 32–36.

79 See BPUFF, above note 5.

80 Schmitt, Michael, “Deconstructing Direct Participation in Hostilities: The Constitutive Elements”, New York University Journal of International Law and Politics, Vol. 42, No. 3, 2010, p. 731Google Scholar.

81 See AP I, Art. 52.

82 ICRC Interpretive Guidance, above note 25, p. 38.

83 Ibid., Recommendation IX.

84 Goodman, Ryan, “The Power to Kill or Capture Enemy Combatants”, European Journal of International Law, Vol. 24, No. 3, 2013, pp. 818–853Google Scholar. See the responses by Corn, Geoff, Blank, Laurie, Jenks, Chris and Jensen, Eric, “Belligerent Targeting and the Invalidity of the Least Harmful Means Rule”, International Legal Studies, Vol. 89, 2013Google Scholar; and Schmitt, Michael, “Wound, Capture or Kill: A Reply to Ryan Goodman's ‘The Power to Kill or Capture Enemy Combatants’”, European Journal of International Law, Vol. 24, No. 3, 2013, pp. 855–861CrossRefGoogle Scholar.

85 See, for example, M. Schmitt, above note 49. See also Parks, W. Hays, “Part IX of the ICRC ‘Direct Participation in Hostilities’ Study: No Mandate, No Expertise, and Legally Incorrect”, New York University Journal of International Law and Politics, Vol. 42, No. 3, 2010, pp. 769–830Google Scholar. See the reply to Parks in N. Melzer, above note 45, pp. 892–913.

86 W. Hays Parks, above note 85, p. 810.

87 ICRC Interpretive Guidance, above note 25, p. 82 (emphasis added).

88 G. Gaggioli, above note 59, p. 17.

89 The term “manifest” is currently used by most armed forces in the context of the duty to disobey a “manifestly unlawful order”. See for example the Queen's Regulations and Orders for the Canadian Forces, Art. 19.015, “Lawful Commands and Orders”.

90 A. Cole et al., above note 34, pp. 39–41.

91 Unless there is no manifest military necessity to use such lethal force. See ICRC Interpretive Guidance, above note 25, Recommendation IX.

92 See BPUFF, above note 5, para. 9.