United States of America
Practice Relating to Rule 146. Reprisals against Protected Persons
The US Field Manual (1956), referring to Article 13 of the 1949 Geneva Convention III, states:
Reprisals against the persons or property of prisoners of war, including the wounded and sick, … are forbidden … However, reprisals may still be visited on enemy troops who have not yet fallen into the hands of the forces making the reprisals. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 497(c).

The US Air Force Pamphlet (1976), referring to Article 13 of the 1949 Geneva Convention III, provides:
Reprisals against prisoners of war are prohibited … No protected person may be punished for an offence he or she has not personally committed. Collective penalties and likewise all measures of intimidation or of terrorism are prohibited. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(1).

The Pamphlet further states:
Reprisals are forbidden, under all circumstances, against the persons or objects referenced above in accordance with the 1949 Geneva Conventions. At least some, and possibly all, of these prohibitions are regarded as customary law and are binding regardless of whether the adversary is a party to the Geneva Conventions. For definitions as to persons or objects protected under the 1949 Geneva Conventions, applicable articles of those documents must be consulted. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(2).

In the chapter dealing with the 1949 Geneva Convention III, the Pamphlet reiterates: “Measures of reprisal against prisoners of war are prohibited.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 13-2.

The US Air Force Commander’s Handbook (1980), under the heading “Persons and Things Not Subject to Reprisals”, states:
Under the 1949 Geneva Conventions, reprisals may not be directed against … prisoners of war. (The reprisals against British prisoners of war that the United States threatened during the Revolution would thus be illegal today, though at the time, reprisals against PWs [prisoners of war] were lawful.) 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 8-4(c).

The US Soldier’s Manual (1984), under the heading “Treat all captives and detainees humanely”, tells soldiers: “You must never engage in reprisals or acts of revenge against any persons, enemy or civilian, whom you capture or detain in combat.” 
United States, Your Conduct in Combat under the Law of War, Publication No. FM 27-2, Headquarters Department of the Army, Washington, November 1984, p. 15.

The US Operational Law Handbook (1993) provides:
The following measures are expressly prohibited by the law of war and are not excusable on the basis of military necessity:

m. Reprisals against persons or property protected by the Geneva Conventions, to include … prisoners of war, detained personnel … 
United States, Operational Law Handbook, JA 422, Center for Law and Military Operations and International Law Division, The Judge Advocate General’s School, United States Army, Charlottesville, Virginia 22903-1781, 1993, p. Q-182.

The US Naval Handbook (1995) states: “Reprisals are forbidden to be taken against: 1. Prisoners of war”. It also provides: “Prisoners of war may not be subjected to collective punishment nor may reprisal action be taken against them.” 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), §§ 6.2.3.2 and 11.7.1.

The Annotated Supplement to the US Naval Handbook (1997), with regard to the prohibition of taking reprisals against prisoners of war, states:
In light of the wide acceptance of the 1949 Geneva Conventions by the nations of the world today, this prohibition is part of customary law … The taking of prisoners by way of reprisal for acts previously committed (so-called “reprisal prisoners”) is likewise forbidden. 
United States, Annotated Supplement to the Commander’s Handbook on the Law of Naval Operations, prepared by the Oceans Law and Policy Department, Center for Naval Warfare Studies, Naval War College, Newport, Rhode Island, November 1997, § 6.2.3.2, footnote 45.

In its judgment in the Dostler case in 1945, in which a German commander had been accused of having ordered, in March 1944, the shooting of 15 American prisoners of war in violation of the 1907 Hague Regulations, the US Military Commission at Rome referred to Article 2, third paragraph, of the 1929 Geneva POW Convention and held that from this provision followed that under the law as codified by this Convention there can be no legitimate reprisals against prisoners of war. No soldier, and still less a Commanding General, could be heard to say that he considered the summary shooting of prisoners of war legitimate even as a reprisal. Referring to the decision of the German Reichsgericht in the Dover Castle case, the US Military Commission of Rome stated that through the express provision of Article 2, third paragraph, of the 1929 Geneva POW Convention the decision of the German Reichsgericht in the said case had lost even such little persuasive authority as it may have had at the time it was rendered. 
United States, Military Commission at Rome, Dostler case, Judgment, 8–12 October 1945.

In April 1965, when a North Vietnamese prisoner was sentenced to death by a South Vietnamese court, the communist rebel group announced that if the sentence was carried out, it would kill an American aid officer in their hands. Neither of the executions was carried out. Three months later, a North Vietnamese prisoner was executed apparently after having been tried, convicted and sentenced by a South Vietnamese special military tribunal. A few days later, it was announced that an American sergeant held as a prisoner of war had been executed in reprisal. In September 1965, three North Vietnamese prisoners were executed, again apparently after having been tried, convicted and sentenced. The execution of two American prisoners of war in reprisal was announced a few days later. 
Frits Kalshoven, Belligerent Reprisals, A. W. Sijthof, Leyden, 1971, pp. 295–305.

The United States refused to accept that the executions were justified as reprisals and the acts were denounced as “two more acts of brutal murder.” The ICRC was asked to take all possible action with respect to these violations. 
United States, Department of State Bulletin, Vol. LIII, No. 1373, 18 October 1965, p. 635.

North Vietnam also threatened to treat captured US pilots as war criminals subject to trial. The United States charged that the threat was to justify reprisals for executions by the South Vietnamese of North Vietnamese prisoners as terrorists. 
N.Y. Times Index, 1965, p. 1098.

An instruction card issued to all US troops engaged in Viet Nam directed soldiers always to treat prisoners humanely, adding: “All persons in your hands, whether suspects, … or combat captives, must be protected against violence, insults, curiosity, and reprisals of any kind.” 
United States, The enemy in your hands, Reproduction of 3x5 instruction card issued to all troops, reprinted in George. S. Prugh, Law at War: Vietnam 1964–1973, Department of the Army, Vietnam Studies, 1975, Appendix H. III.

At the 20th International Conference of the Red Cross in 1965, the US delegate declared that his government had been “shocked and deeply saddened by the brutal murder of prisoners of war as acts of reprisals” in the Vietnam War and that it was “profoundly concerned that other prisoners may be executed in violation of international law”. 
United States, Department of State Bulletin, Vol. LIII, No. 1375, 1 November 1965, p. 725.

According the Report on US Practice: “The United States does not regard the summary execution of persons in custody as a lawful means of reprisals.” 
Report on US Practice, 1997, Chapter 2.9.

The US Field Manual (1956), referring to Article 13 of the 1949 Geneva Convention III and Article 33 of the 1949 Geneva Convention IV, provides:
Reprisals against the persons or property of prisoners of war, including the wounded and sick, … are forbidden … However, reprisals may still be visited on enemy troops who have not yet fallen into the hands of the forces making the reprisals. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 497(c).

The US Air Force Pamphlet (1976), referring to Article 46 of the 1949 Geneva Convention I and Article 47 of the 1949 Geneva Convention II, provides:
Reprisals against the wounded [and] sick … protected by [the 1949 Geneva Convention I] are prohibited …
Reprisals against the wounded, sick and shipwrecked persons … protected by [the 1949 Geneva Convention II] are prohibited …
No protected person may be punished for an offence he or she has not personally committed. Collective penalties and likewise all measures of intimidation or of terrorism are prohibited. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(1).

The Pamphlet further states:
Reprisals are forbidden, under all circumstances, against the persons or objects referenced above in accordance with the 1949 Geneva Conventions. At least some, and possibly all, of these prohibitions are regarded as customary law and are binding regardless of whether the adversary is a party to the Geneva Conventions. For definitions as to persons or objects protected under the 1949 Geneva Conventions, applicable articles of those documents must be consulted.  
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(2).

The US Air Force Commander’s Handbook (1980), under the heading “Persons and Things Not Subject to Reprisals”, states: “Under the 1949 Geneva Conventions, reprisals may not be directed against … the sick and wounded [and] the shipwrecked”. 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 8-4(c).

The US Operational Law Handbook (1993) provides:
The following measures are expressly prohibited by the law of war and are not excusable on the basis of military necessity:

m. Reprisals against persons or property protected by the Geneva Conventions, to include the wounded, sick, or shipwrecked. 
United States, Operational Law Handbook, JA 422, Center for Law and Military Operations and International Law Division, The Judge Advocate General’s School, United States Army, Charlottesville, Virginia 22903-1781, 1993, p. Q-182.

The US Naval Handbook (1995) states: “Reprisals are forbidden to be taken against: … 2. Wounded, sick and shipwrecked persons.” 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 6.2.3.2.

In 1987, the Deputy Legal Adviser of the US Department of State, mentioning that the protection of the wounded, sick and shipwrecked was an area in which the 1977 Additional Protocol I “does contain some useful codifications or improvements of existing rules”, affirmed: “We support the principle that all the wounded, sick, and shipwrecked be respected and protected, and not be made the object of attacks or reprisals, regardless of the party to the conflict to which they belong.” 
United States, Remarks of Michael J. Matheson, Deputy Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, American Journal of International Law and Policy, Vol. 2, 1987, p. 423.

In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United States noted that it considered that the provisions of the 1977 Additional Protocol I regarding reprisals were “new rules”. 
United States, Written statement submitted to the ICJ, Nuclear Weapons case, 20 June 1995, p. 31.

The US Air Force Pamphlet (1976), referring to Article 46 of the 1949 Geneva Convention I and Article 47 of the 1949 Geneva Convention II, provides:
Reprisals against the … personnel … protected by [the 1949 Geneva Convention I] are prohibited …
Reprisals against … the persons protected by [the 1949 Geneva Convention II] are prohibited …
No protected person may be punished for an offence he or she has not personally committed. Collective penalties and likewise all measures of intimidation or of terrorism are prohibited. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(1).

The Pamphlet further states:
Reprisals are forbidden, under all circumstances, against the persons or objects referenced above in accordance with the 1949 Geneva Conventions. At least some, and possibly all, of these prohibitions are regarded as customary law and are binding regardless of whether the adversary is a party to the Geneva Conventions. For definitions as to persons or objects protected under the 1949 Geneva Conventions, applicable articles of those documents must be consulted. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(2).

The US Air Force Commander’s Handbook (1980), under the heading “Persons and Things Not Subject to Reprisals”, states: “Under the 1949 Geneva Conventions, reprisals may not be directed against … medical personnel”. 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 8-4(c).

The US Operational Law Handbook (1993) provides:
The following measures are expressly prohibited by the law of war and are not excusable on the basis of military necessity:

m. Reprisals against persons or property protected by the Geneva Conventions. 
United States, Operational Law Handbook, JA 422, Center for Law and Military Operations and International Law Division, The Judge Advocate General’s School, United States Army, Charlottesville, Virginia 22903-1781, 1993, p. Q-182.

The US Naval Handbook (1995) states: “Reprisals are forbidden to be taken against: … 4. Hospitals and medical facilities, personnel, and equipment.” 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 6.2.3.2.

In 1987, the Deputy Legal Adviser of the US Department of State, referring to Articles 12–20 the 1977 Additional Protocol I, affirmed: “We … support the principle that medical units, including properly authorized civilian medical units, be respected and protected at all times and not be the object of attacks or reprisals.” 
United States, Remarks of Michael J. Matheson, Deputy Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, American Journal of International Law and Policy, Vol. 2, 1987, p. 423.

In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United States noted that it considered that the provisions of the 1977 Additional Protocol I regarding reprisals were “new rules”. 
United States, Written statement submitted to the ICJ, Nuclear Weapons case, 20 June 1995, p. 31.

The US Field Manual (1956), referring to Article 33 of the 1949 Geneva Convention IV, states: “Reprisals against … protected civilians are forbidden … However, reprisals may still be visited on enemy troops who have not yet fallen into the hands of the forces making the reprisals.” 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 497(c).

The US Air Force Pamphlet (1976), referring to Article 33 of the 1949 Geneva Convention IV, provides:
No protected person may be punished for an offence he or she has not personally committed. Collective penalties and likewise all measures of intimidation or of terrorism are prohibited. Reprisals against protected persons … are prohibited. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(1).

The Pamphlet further states:
Reprisals are forbidden, under all circumstances, against the persons or objects referenced above in accordance with the 1949 Geneva Conventions. At least some, and possibly all, of these prohibitions are regarded as customary law and are binding regardless of whether the adversary is a party to the Geneva Conventions. For definitions as to persons or objects protected under the 1949 Geneva Conventions, applicable articles of those documents must be consulted. Also, the prohibition in Article 33, [Geneva Convention IV], protecting civilians includes all those who … at a given moment and in any manner whatsoever, find themselves, in case of a conflict or occupation, in the hands of a Party to the conflict or Occupying Power of which they are not nationals. (Article 4, [Geneva Convention IV]). 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(2).

The US Soldier’s Manual (1984), under the heading “Treat all captives and detainees humanely”, tells soldiers: “You must never engage in reprisals or acts of revenge against any persons, enemy or civilian, whom you capture or detain in combat.” 
United States, Your Conduct in Combat under the Law of War, Publication No. FM 27-2, Headquarters Department of the Army, Washington, November 1984, p. 15.

In a part dealing with the treatment of civilians and private property, the manual further states: “The Geneva Conventions forbid retaliating against civilians for the actions of enemy soldiers.” 
United States, Your Conduct in Combat under the Law of War, Publication No. FM 27-2, Headquarters Department of the Army, Washington, November 1984, p. 23.

The US Air Force Commander’s Handbook (1980), under the heading “Persons and Things Not Subject to Reprisals”, states: “Under the 1949 Geneva Conventions, reprisals may not be directed against … the inhabitants of occupied territory”. 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 8-4(c).

The US Operational Law Handbook (1993) provides: “The following measures are expressly prohibited by the law of war and are not excusable on the basis of military necessity: … m. Reprisals against persons or property protected by the Geneva Conventions, to include … civilians.” 
United States, Operational Law Handbook, JA 422, Center for Law and Military Operations and International Law Division, The Judge Advocate General’s School, United States Army, Charlottesville, Virginia 22903-1781, 1993, p. Q-182.

The US Naval Handbook (1995) states: “Reprisals are forbidden to be taken against: 1. … interned civilians … 3. Civilians in occupied territory.”  
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 6.2.3.2.

The Handbook also provides: “All interned civilians … may not be subjected to reprisal action or collective punishment.” 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 11.8.

In the Calley case in 1973, a US army officer was convicted of murder for killing South Vietnamese civilians. The US Army Court of Military Review dismissed the argument that the acts were lawful reprisals for illegal acts of the enemy and held: “Slaughtering many for the presumed delicts of a few is not a lawful response to the delicts … Reprisal by summary execution of the helpless is forbidden in the laws of land warfare.” 
United States, Army Court of Military Review, Calley case, Judgment, 16 February 1973.

An instruction card issued to all US troops engaged in Viet Nam directed soldiers always to treat prisoners humanely, adding: “All persons in your hands, whether suspects [or] civilians … must be protected against violence, insults, curiosity, and reprisals of any kind.” 
United States, The enemy in your hands, Reproduction of 3x5 instruction card issued to all troops, reprinted in George. S. Prugh, Law at War: Vietnam 1964–1973, Department of the Army, Vietnam Studies, 1975, Appendix H. III.

In 1980, in a footnote to a memorandum of law on the “Reported Use of Chemical Agents in Afghanistan, Laos, and Kampuchea”, a legal adviser of the US Department of State stated:
In theory, an attempt might also be made to justify the use of chemical weapons in Afghanistan as a lawful reprisal against violations of the general laws of war by Afghan insurgents (such as the summary execution of Soviet prisoners). However, such an argument would face several serious problems. First, the prohibition in the [1925 Geneva Gas] Protocol and in customary international law apparently itself precludes use of chemical weapons in reprisal except in response to enemy use of weapons prohibited by the [1925 Geneva Gas] Protocol … Second, reprisals against the civilian population of occupied territories are expressly precluded by the law of war, and this would apply to reprisals against Afghan villages in areas occupied by Soviet forces. See Article 33 of [the 1949 Geneva Convention IV]. 
United States, Department of State, Memorandum of law by a Legal Adviser on the “Reported Use of Chemical Agents in Afghanistan, Laos, and Kampuchea”, 9 April 1980, reprinted in Marian Nash Leich, Digest of United States Practice in International Law, 1980, Department of State Publication 9610, Washington, D.C., December 1986, pp. 1034 and 1041, footnote 38.

The US Air Force Pamphlet (1976), referring to Articles 4 and 33 of the 1949 Geneva Convention IV, states: “The protection against reprisals expressed in the Conventions … does not protect civilians who are under the control of their own country.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-7(b)(2).

The US Air Force Commander’s Handbook (1980), under the heading “Persons and Things Not Subject to Reprisals”, lists a number of persons and objects protected under the 1949 Geneva Conventions against which it is prohibited to take reprisals, among which are “inhabitants of occupied territory”. The Handbook adds, however: “A Protocol to the 1949 Geneva Conventions would expand this list to include all civilians … The United States signed this Protocol in 1977, but has not yet ratified it. Consult the Staff Judge Advocate for further guidance.” 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 8-4(c).

The US Naval Handbook (1995) provides: “Reprisals may be taken against enemy armed forces, enemy civilians other than those in occupied territory, and enemy property.” 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 6.2.3.

At the CDDH, the United States stated:
[The 1977 Additional Protocol I] had gone far to remove the deterrent of reprisals, for understandable and commendable reasons and in view of past abuses. In the event of massive and continuing violations of the [1949 Geneva] Conventions and [the 1977 Additional Protocol I], however, the series of prohibitions on reprisals might prove unworkable. Massive and continuing attacks directed against a nation’s civilian population could not be absorbed without a response in kind. By denying the possibility of such response and not offering any workable substitute, [the 1977 Additional Protocol I] was unrealistic and, in that respect, could not be expected to withstand the test of future armed conflicts. 
United States, Statement at the CDDH, Official Records, Vol. VII, CDDH/SR.58, 9 June 1977, p. 294, § 81.

In 1987, in submitting the 1977 Additional Protocol II to the US Senate for advice and consent to ratification, the US President announced his decision not to ratify the 1977 Additional Protocol I, stating, inter alia, that the 1977 Additional Protocol I “fails to improve substantially the compliance and verification mechanisms of the 1949 Geneva Conventions and eliminates an important sanction against violations of those Conventions”. 
United States, Message from the US President transmitting the 1977 Additional Protocol II to the US Senate for advice and consent to ratification, Treaty Doc. 100-2, 29 January 1987.

In 1987, the Deputy Legal Adviser of the US Department of State stated that the United States did not support “the prohibition on reprisals in article 51 and subsequent articles” and did not consider it part of customary law. 
United States, Remarks of Michael J. Matheson, Deputy Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, American Journal of International Law and Policy, Vol. 2, 1987, p. 426.

On the same occasion, another Legal Adviser of the US Department of State, explaining “the position of the United States on current law of war agreements”, stated:
Article 51 of Protocol I prohibits any reprisal attacks against the civilian population, that is, attacks that would otherwise be forbidden but that are in response to the enemy’s own violations of the law and are intended to deter future violations. Historically, reciprocity has been the major sanction underlying the laws of war. If article 51 were to come into force for the United States, an enemy could deliberately carry out attacks against friendly civilian populations, and the United States would be legally forbidden to reply in kind. As a practical matter, the United States might, for political or humanitarian reasons, decide in a particular case not to carry out retaliatory or reprisal attacks involving unfriendly civilian populations. To formally renounce even the option of such attacks, however, removes a significant deterrent that presently protects civilians and other war victims on all sides of a conflict. 
United States, Remarks of Judge Abraham D. Sofaer, Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, 22 January 1987, American University Journal of International Law and Policy, Vol. 2, 1987, p. 469.

According to an army lawyer who participated in the review of the 1977 Additional Protocol I by the US Joint Chiefs of Staff:
Article 51, paragraph 6, and article 52, paragraph 1, of [the 1977 Additional Protocol I] prohibit reprisals against the civilian population or civilian objects of an enemy nation, respectively. These provisions are not a codification of customary international law, but, in fact, a reversal of that law. The military review considered whether surrender of these rights would advance the law of war, or threaten the continued respect for the rule of law in war. It was concluded that removal of this legal right placed any further respect for the rule of law by certain nations in jeopardy …
The American review recognized the historic pattern for abuse of U.S. and allied prisoners of war by their enemies, and concluded that a broad reservation to the prohibition of reprisals contained in articles 51 and 52 of [the 1977 Additional Protocol I] was essential as a legitimate enforcement mechanism in order to ensure respect for the law of war. 
W. Hays Parks, “Air War and the Law of War”, Air Force Law Review, Vol. 32, 1990, pp. 94 and 97.

In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United States stated:
Various provisions of Additional Protocol I contain prohibitions on reprisals against specific types of persons or objects, including the civilian population or individual civilians (Article 51(6)) … These are among the new rules established by the Protocol that … do not apply to nuclear weapons. 
United States, Written statement submitted to the ICJ, Nuclear Weapons case, 20 June 1995, p. 31.

According to the Report on US Practice, during the review of the 1977 Additional Protocol I by the US government prior to the decision on whether to seek its ratification, the discussion of the reprisal issue shifted from the need to deter attacks on civilians to the need to protect US prisoners of war by enforcing the 1949 Geneva Convention III. 
Report on US Practice, 1997, Chapter 2.9.