Related Rule
United States of America
Practice Relating to Rule 27. Religious Personnel
The US Field Manual (1956) restates Article 24 of the 1949 Geneva Convention I. 
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, § 67.
The US Naval Handbook (1995) states: “Chaplains attached to the armed forces are entitled to respect and protection.” 
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), § 11.5.
The Annotated Supplement to the US Naval Handbook (1997) notes: “The United States supports the principle in [Article 15 of the 1977 Additional Protocol I] that civilian … religious personnel be respected and protected and not be made the objects of attack.” 
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, § 11.5, footnote 31.
The US Naval Handbook (2007) states: “Chaplains attached to the armed forces are entitled to respect and protection.” 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/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 Homeland Security, US Coast Guard, July 2007, § 8.2.4.2.
The Handbook also states:
Noncombatants [§ 5.4.2. – “Noncombatants are those members of the armed forces who do not take direct part in hostilities because of their status as medical personnel and chaplains”] may not be deliberately or indiscriminately attacked, unless they forgo their protection by taking a direct part in hostilities. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/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 Homeland Security, US Coast Guard, July 2007, § 6.2.6.
The Handbook also states:
[C]haplains falling into enemy hands … unless their retention by the enemy is required to provide for the … religious needs of prisoners of war, … must be repatriated at the earliest opportunity. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/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 Homeland Security, US Coast Guard, July 2007, § 11.4.
The US Manual for Military Commissions (2010), Part IV, Crimes and Elements, states: “The term ‘protected person’ means any person entitled to protection under one or more of the [1949] Geneva Conventions, including … military … religious personnel.” 
United States, Manual for Military Commissions, published in implementation of Chapter 47A of Title 10, United States Code, as amended by the Military Commissions Act of 2009, 10 U.S.C, §§ 948a, et seq., 27 April 2010, § 1(a)(2)(C), p. IV-1.
The US Military Commissions Act (2006), passed by Congress following the Supreme Court’s decision in Hamdan v. Rumsfeld in 2006, amends Title 10 of the United States Code as follows:
§ 950v. Crimes triable by military commissions
“(a) DEFINITIONS AND CONSTRUCTION. – In this section:
“ …
“(2) PROTECTED PERSON. – The term “protected person” means any person entitled to protection under one or more of the Geneva Conventions, including –
“ …
“(C) military medical or religious personnel. 
United States, Military Commissions Act, 2006, Public Law 109-366, Chapter 47A of Title 10 of the United States Code, 17 October 2006, p. 120 Stat. 2625, § 950v (a) (2) (C).
The US Military Commissions Act (2009) amends Chapter 47A of Title 10 of the United States Code as follows:
§ 950p. Definitions; construction of certain offenses; common circumstances
“(a) DEFINITIONS.—In this subchapter:
“ …
“ (2) The term ‘protected person’ means any person entitled to protection under one or more of the [1949] Geneva Conventions, including … military … religious personnel. 
United States, Military Commissions Act, 2009, § 950p(a)(2).
David Hicks, an Australian citizen, was captured in Afghanistan in December 2001 and afterwards detained at Guantanamo Bay Naval Base, Cuba. In March 2007, in the Hicks case, the accused became the first person to be tried and convicted under the US Military Commissions Act of 2006. Following a pre-trial agreement struck with the Convening Authority, the accused pleaded guilty to the charge of “providing material support for terrorism”. In April 2007, Hicks returned to Australia to serve the remaining nine months of a suspended seven-year sentence. In the case’s record of trial for the 30 March 2007 hearing, the military judge defined various terms contained in the charge to which the accused had pleaded guilty:
“Protected person” means any person entitled to protection under one or more of the Geneva Conventions, including: (a) civilians not taking part in hostilities; (b) military personnel placed hors de combat by sickness, wounds, or detention; and (c) military medical or religious personnel. 
United States, Office of Military Commissions, Hicks case, Record of Trial, 26 and 30 March 2007.
In 1987, the Deputy Legal Adviser of the US Department of State affirmed that “we support the principle that medical and religious personnel must be respected and protected” as provided in Article 15 of the 1977 Additional Protocol I. 
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 University Journal of International Law and Policy, Vol. 2, 1987, p. 423.
Upon signature of the 1977 Additional Protocols I and II, the United States declared:
It is the understanding of the United States of America that the terms used in Part III of [the 1977 Additional Protocol II] which are the same as the terms defined in Article 8 [of the 1977 Additional Protocol I] shall so far as relevant be construed in the same sense as those definitions. 
United States, Declaration made upon signature of the 1977 Additional Protocols I and II, 12 December 1977, § B.
According to the Report on US Practice, it is the opinio juris of the United States that medical and religious personnel are not to be knowingly attacked or unnecessarily prevented from performing their duties in either international or non-international armed conflicts. 
Report on US Practice, 1997, Chapter 2.7.