Related Rule
United States of America
Practice Relating to Rule 6. Civilians’ Loss of Protection from Attack
Section C. Situations of doubt as to the character of a person
According to the Report on US Practice, the US military manuals do not adopt the position that in case of doubt a person shall be considered as civilian. 
Report on US Practice, 1997, Chapter 1.1, referring to: 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, § 60; Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 5-3; and 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), § 11.3.