text: Chapter 3
  use made of the emblem and must see that it is not improperly used by the troops or by
  individuals.
  * Article 42 of the GWS specifically addresses the marking of medical units and establishments.
   “The distinctive flag of the Convention shall be hoisted only over such medical units and
  establishments as are entitled to be respected under the Convention, and only with the consent
  of the military authorities.” (Paragraph 1, Article 42, GWS.) Although the Convention does
  not define “the distinctive flag of the Convention,” what is meant is a white flag with a Red
  Cross in its center. Also, the word “flag” must be taken in its broadest sense. Hospitals are
  often marked by one or several Red Cross emblems painted on the roof. Finally, the military
  authority must consent to the use of the flag (see the above comments on Article 39) and must
  ensure that the flag is used only on buildings entitled to protection.
   “In mobile units, as in fixed establishments, it [the distinctive flag] may be accompanied by
  the national flag of the Party to the conflict to which the unit or establishment belongs.”
  (Article 42, GWS.) This provision makes it optional to fly the national flag with the Red
  Cross flag. It should be noted that in an operational area the national flag is a symbol of
  belligerency and is therefore likely to provoke attack.
   In a NATO conflict, NATO STANAG 2931 provides for camouflage of the Geneva emblem
  on medical facilities where the lack of camouflage might compromise operations. Medical
  facilities on land, supporting forces of other nations, will display or camouflage the Geneva
  emblem in accordance with national regulations and procedures. When failure to camouflage
  would endanger or compromise operational operations, the camouflage of medical facilities
  may be ordered by a NATO commander of at least brigade level or equivalent. Such an order
  is to be temporary and local in nature and countermanded as soon as the circumstances permit.
  It is not envisaged that fixed, large, medical facilities would be camouflaged. The STANAG
  defines “medical facilities” as “medical units, medical vehicles, and medical aircraft on the
  ground.”
  Note. There is no such thing as a “camouflaged” Red Cross. When camouflaging a medical unit
  either cover up the Red Cross or take it down. A black cross on an olive drab or any other
  background is not a symbol recognized under the Geneva Conventions.
  3-24. For additional guidance on the marking of air ambulances, refer to AR 40-3 and TM 1-1500-345-23.
  For more information on approved medical symbols, refer to Appendix F.
  LOSS OF PROTECTION OF MEDICAL ESTABLISHMENTS AND UNITS
  3-25. Medical assets lose their protected status by committing acts “harmful to the enemy.” (Article 21,
  GWS.) A warning must be given to the offending unit and a reasonable amount of time allowed to cease
  such activity.
  ACTS HARMFUL TO THE ENEMY
  3-26. The phrase “acts harmful to the enemy” is not defined in the Convention, but should be considered to
  include acts the purpose or effect of which is to harm the enemy, by facilitating or impeding military
  operations. Such harmful acts would include, for example, the use of a hospital as a shelter for able-bodied
  combatants, as an arms or ammunition dump, or as a military observation post. Another instance would be
  the deliberate sitting of a medical unit in a position where it would impede an enemy attack.
  WARNING AND TIME LIMIT
  3-27. The enemy has to warn the unit to put an end to the harmful acts and must fix a time limit on the
  conclusion of which he may open fire or attack if the warning has not been complied with. The phrase in all
  appropriate cases recognizes that there might obviously be cases where no time limit could be allowed. A
  body of troops approaching a hospital and met by heavy fire from every window would return fire without
  delay.