Part II: Rules of Air Warfare#Chapter III: Belligerents. - Art. 17.
Art. 17. The principles laid down by the Geneva Conference of 1906 and under the Convention for the adaptation of the said Convention to maritime warfare (Convention X of 1907) shall apply to air warfare and to ambulance planes as well as to the control of such ambulance planes by belligerent commanders.
In order to enjoy the protection and the privileges granted to mobile sanitary units by the Geneva Convention of 1906, the ambulance planes must carry, in addition to their normal distinctive marks, the distinctive emblem of the Red Cross.