Related Rule
United States of America
Practice Related to Rule 95. Forced Labour
Section B. Compelling persons to serve in the forces of a hostile power
The US Field Manual (1956) provides that compelling a prisoner of war or a protected person to serve in the forces of a hostile power is a grave breach of the 1949 Geneva Conventions. 
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, §§ 418 and 502.
The US Air Force Pamphlet (1976) recalls Article 23 of the 1907 Hague Regulations, which “forbids compelling nationals of the hostile party to take part in the operations of war directed against their own country”, and Article 45 of the 1907 Hague Regulations, which “forbids compelling the inhabitants of occupied territory to swear allegiance to the hostile power”. The Pamphlet also refers to Article 51 of the 1949 Geneva Convention IV and states: “Compulsory military service by protected persons in the armed forces of the occupant is prohibited.” It adds: “Wilfully compelling civilians or PWs [prisoners of war] to perform prohibited labour” is an act involving individual criminal responsibility.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, §§ 14-6(a) and (b) and 15-3(c)(9).
The US Air Force Commander’s Handbook (1980): “A belligerent is likewise forbidden to compel the nationals of the hostile party to take part in the operations of war directed against their own country.” 
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, § 32.
Under the US War Crimes Act (1996), violations of common Article 3 of the 1949 Geneva Conventions, grave breaches of the 1949 Geneva Conventions and violations of Article 23 of the 1907 Hague Regulations are war crimes. 
United States, War Crimes Act, 1996, Section 2441(c).
In its judgement in the Weizsaecker case (The Ministries Trial) in 1949, the US Military Tribunal at Nuremberg held that “pressure or coercion to compel [prisoners of war] to enter into the armed forces obviously violated international law” and that the conscription of foreign nationals into the armed forces of a belligerent was a crime against humanity. 
United States, Military Tribunal at Nuremberg, Weizsaecker case (The Ministries Trial), Judgment, 14 April 1949.
In 1992, in its final report to Congress on the conduct of the Gulf War, the US Department of Defense stated: “Compelling hostages to serve in the armed forces of Iraq constitute Grave Breaches (that is, major violations of the law of war) under Article 147 [of the 1949 Geneva Convention IV].” 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Appendix O, The Role of the Law of War, ILM, Vol. 31, 1992, p. 618.
The report also listed some specific Iraqi war crimes including “compelling Kuwaiti and third country nationals to serve in the armed forces of Iraq, in violation of Articles 51 and 147 [of the 1949 Geneva Convention IV]”. 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Appendix O, The Role of the Law of War, ILM, Vol. 31, 1992, p. 634.