Related Rule
United States of America
Practice Relating to Rule 10. Civilian Objects’ Loss of Protection from Attack
Section B. Situations of doubt as to the character of an object
The US Air Force Pamphlet (1976) states:
In case of doubt whether an object which is normally dedicated to civilian purposes, such as a house or other dwelling or a school, is being used to make an effective contribution to military action, it shall be presumed not to be so used. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 5-3(a)(1)(b).
In 1992, in its final report to Congress on the conduct of the Gulf War, the US Department of Defense commented thus on Article 52(3) of the 1977 Additional Protocol I:
This language, which is not a codification of the customary practice of nations, causes several things to occur that are contrary to the traditional law of war. It shifts the burden for determining the precise use of an object from the party controlling that object (and therefore in possession of the facts as to its use) to the party lacking such control and facts, i.e. from defender to attacker. This imbalance ignores the realities of war in demanding a degree of certainty of an attacker that seldom exists in combat. It also encourages a defender to ignore its obligation to separate the civilian population, individual civilians and civilian objects from military objectives, as the Government of Iraq illustrated during the Persian Gulf War. 
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. 627.
Noting that the US Naval Handbook does not refer to such presumption, the Report on US Practice concludes that the US Government does not acknowledge the existence of a customary principle requiring a presumption of civilian character in case of doubt. 
Report on US Practice, 1997, Chapter 1.3.