Related Rule
United States of America
Practice Relating to Rule 15. The Principle of Precautions in Attack
Section D. Information required for deciding upon precautions in attack
The US Naval Handbook (1995) states:
The commander must decide, in light of all the facts known or reasonably available to him, including the need to conserve resources and complete the mission successfully, whether to adopt an alternative method of attack, if reasonably available, to reduce civilian casualties and damage. 
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), § 8.1.2.1.
The US Naval Handbook (2007) states:
[T]he commander must decide, in light of all the facts known or reasonably available to him, including the need to conserve resources and complete the mission successfully, whether to adopt an alternative method of attack, if reasonably available, to reduce civilian casualties and damage. 
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, § 8.3.1.
In 1992, in its final report to Congress on the conduct of the Gulf War, the US Department of Defense stated:
In reviewing an incident such as the attack of the Al-’Amariyah bunker, the law of war recognizes the difficulty of decision making amid the confusion of war. Leaders and commanders necessarily have to make decisions on the basis of their assessment of the information reasonably available to them at the time, rather than what is determined in hindsight. 
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. 626.