Related Rule
Germany
Practice Relating to Rule 145. Reprisals
Section C. Proportionality of reprisals
Germany’s Military Manual (1992) provides: “Reprisals shall not be excessive in relation to the offence committed by the adversary.” 
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, § 478.