Related Rule
Practice Relating to Rule 29. Medical Transports
Section B. Respect for and protection of medical aircraft
Germany’s Military Manual (1992) states:
The parties to the conflict are prohibited from using their medical aircraft to attempt to acquire any military advantage over an adverse party. The presence of medical aircraft shall not be used in an attempt to render military objectives immune from attack. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 620.