Related Rule
United States of America
Practice Relating to Rule 9. Definition of Civilian Objects
The US Air Force Pamphlet (1976) states: “Civilian objects are all objects which are not military objectives.” 
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).
The US Naval Handbook (1995) defines civilian objects as “all civilian property and activities other than those used to support or sustain the enemy’s war-fighting capability”. 
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), § 8.1.2.
The US Naval Handbook (2007) states: “Civilian objects consist of all objects that are not military objectives”. 
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, § 8.3.