Another aspect, is that any vehicle marked as an ambulance vehicle, under no circumstances, is permitted to have any kind of weapon at all. It is covered by several clauses of the Geneva Convention.

223. Conditions Not Depriving Medical Units and Establishments of
Protection
a. Treaty Provision.
The following conditions shall not be considered as depriving a medical unit or establishment of the protection guaranteed by Article 19:
(1) That the personnel of the unit or establishment are armed, and that they use the arms in their own defense, or in that of the wounded and sick in their charge.
(2) That in the absence of armed orderlies, the unit or establishment is protected by a picket or by sentries or by an escort.
(3) That small arms and ammunition taken from the wounded and sick and not yet handed to the proper service, are found in the unit or establishment.
(4) That personnel and material of the veterinary service are found in the unit or establishment, without forming an integral part thereof.
(5) That the humanitarian activities of medical units and establishments or of their personnel extend to the care of civilian wounded or sick. (GWS, art. 22.)
b. Self-Defense Defined. Although medical personnel may carry arms for self-defense, they may not employ such arms against enemy forces acting in conformity with the law of war. These arms are for their personal defense and for the protection of the wounded and sick under their charge against marauders and other persons violating the law of war. Medical personnel who use their arms in circumstances not justified by the law of war expose themselves to penalties for violation of the law of war and, provided they have been given due warning to cease such acts, may also forfeit the protection of the medical unit or establishment of which they form part or which they are protecting.
c. Arms and Ammunition Taken From the Wounded and Sick.
As provided in substance by the foregoing article, the presence of such arms and ammunition in a medical unit or establishment is not of itself cause for denying the protection to be accorded such organizations under GWS. However, such arms and ammunition should be turned in as soon as practicable and, in any event, are subject to confiscation.