text: General Background and Basic Principles of the Law of Armed Conflict
  and irreconcilably flawed” and there were major objections to certain provisions of Additional Protocol I
  (for example, arts. 1(4), 43(1), 44(3), among others), President Reagan also noted “this agreement has certain
  meritorious elements,” and the United States would support “the positive provisions of Protocol I that could
  be of real humanitarian benefit if generally observed by parties to international armed conflicts.” Letter of
  Transmittal for Additional Protocol II, President Ronald W. Reagan, to the Senate of the United States, 23
  Weekly Compilation of Presidential Documents, 91 (Jan. 29, 1987) (quoting a passage in the letter addressing
  AP I). Consistent with this approach, for example, the Obama Administration announced, “[a]lthough the
  Administration continues to have significant concerns with Additional Protocol I,” the United States
  “choose[s] out of a sense of legal obligation to treat the principles set forth in Article 75 [of AP I] as applicable
  to any individual it detains in an international armed conflict[.]” New Actions on Guantanamo and Detainee
  Policy Fact Sheet, March 2011. http://www.whitehouse.gov/the-press-office/2011/03/07/fact-sheet-new-
  actions-guant-namo-and-detainee-policy.
  1-100. While the United States is not bound by Additional Protocol I, U.S. practice is consistent with much
  of the protocol and many of its provisions support principles that the United States espouses. Further, U.S.
  Armed Forces have often fought as a multinational partner in armed conflicts alongside countries who are
  parties to Additional Protocol I. In those conflicts, U.S. military forces, as a matter of practice, have acted
  consistent with many of its provisions. In addition, later treaties to which the United States is a party have
  incorporated some Additional Protocol I provisions. For example, Additional Protocol I’s definition of
  military objective is essentially the same as the definition in CCW protocols. (Compare AP I art. 52(2) with
  CCW Amended Protocol II art. 2(6) and CCW Protocol III art. 1(3)). This publication references AP I
  provisions, some of which are consistent with U.S. practice. Unless explicitly noted, no determinations are
  made about whether any of these provisions reflect customary international law. For more information about
  DOD views with regard to particular AP I provisions, judge advocates should refer to the DOD Law of War
  Manual (DOD Law of War Manual, 19.20.1).
  CUSTOMARY INTERNATIONAL LAW
  1-101. Customary international law results from a general and consistent practice of States followed from
  a sense of legal obligation (opinio juris). Unlike a treaty provision, which is readily accessible in an
  identifiable document that sets forth an agreed-upon, codified rule, it can be difficult to identify and assess
  evidence of State practice and opinio juris when seeking to determine whether State actions in a particular
  area have resulted in a rule of customary international law. As with issues of treaty applicability and
  interpretation, questions on customary international law should be referred to judge advocates, and judge
  advocates should refer specific questions through their operational chain of command for resolution to ensure
  that there are common understandings of the customary international law requirements during military
  operations.
  1-102. Customary law often may be ascertained using subsidiary means, such as judicial decisions, official
  statements by governments, and the teachings of the most highly qualified publicists of various nations.
  Discretion is necessary in weighing sources, however, as some sources are more reliable than others.
  1-103. The customary LOAC applies to all cases of declared war or any other armed conflict, even if a party
  to the conflict does not recognize the state of war. The customary LOAC also applies to all cases of
  occupation of foreign territory by the exercise of armed force, even if the occupation meets with no armed
  resistance. It is also important to understand that customary international law applicable in an international
  armed conflict may, in certain respects, be different from customary international law applicable in a non-
  international law armed conflict.
  THE LAW OF ARMED CONFLICT AS U.S. LAW
  1-104. Army and Marine Corps personnel should treat and observe all treaties in force for the United States
  as federal law. Similarly, Army and Marine Corps personnel should treat and observe customary LOAC as
  part of U.S. law.