text: Conduct of Hostilities
  Warning Before Attack
  Unless circumstances do not permit, effective advance warning must be given of an attack that may
  affect the civilian population (see DOD Law of War Manual, 5.11.5; HR art. 26; Hague IX art. 6; consider
  AP I art. 57(2)(c)).
  Effective Advance Warning
  LOAC has no set form for warnings. Warnings may be general, communicated to the national
  leadership of the enemy State, or delivered to the civilian population through military information support
  operations (MISO), to advise the civilian population of risk of injury if they remain near military objectives.
  Giving the specific time and place of an attack is not required. Warnings have been used by U.S. forces
  conducting bombardments in prior conflicts, such as World War II, the Korean War, the 1990-1991 Gulf
  War, the 2003 Iraq War, and the armed conflict against al Qaeda, the Taliban, and associated forces.
  That May Affect the Civilian Population
  The purpose of warning is to facilitate the protection of the civilian population so that it can take
  measures to avoid the dangers inherent in military operations. If the civilian population will not be affected,
  then there is no obligation to provide a warning to facilitate their protection.
  Unless Circumstances Do Not Permit
  A warning is not required if circumstances do not permit. Such circumstances include legitimate
  military reasons, such as exploiting the element of surprise in order to provide for mission accomplishment
  and preserve the attacking force.
  Adjusting the Timing of the Attack
  Adjusting the timing of an attack may reduce the risk of incidental harm (see DOD Law of War Manual,
  5.11.3; consider AP I art. 57(2)(b)). For example, attacking a military objective when civilians are less likely
  to be present may be appropriate. Similarly, waiting until enemy forces have departed from populated areas
  before attacking such forces may be appropriate in order to reduce the risk of incidental harm to civilians and
  civilian objects.
  Selecting Weapons (Weaponeering)
  Depending on the circumstances, the use of certain weapons rather than others may lower the risk of
  incidental harm while offering the same or superior military advantage in neutralizing or destroying a military
  objective. For example, employing incendiary weapons may be advantageous in attacking an adversary’s
  repository of biological weapons so as to prevent the biological agents from adversely affecting the civilian
  population. Similarly, under certain circumstances, using precision-guided munitions may be advantageous
  to minimize the risk of incidental harm.
  As with other precautions, the decision on which weapon to use will be subject to many practical
  considerations, including effectiveness, cost, and the need to preserve capabilities for other engagements. For
  example, a commander may decide not to use precision-guided munitions because he or she determines it is
  necessary to preserve that capability for another engagement.
  LAWFULNESS OF CERTAIN METHODS OF WAGING WARFARE
  This section examines LOAC rules governing attacks against military objectives, attacks that could
  unleash dangerous forces, protections for undefended population centers, starvation, and environmental
  concerns.