Related Rule
Germany
Practice Relating to Rule 57. Ruses of War
Germany’s Military Manual (1992) provides:
Ruses of war and the employment of measures necessary for obtaining information about the adverse party and the country are considered permissible … Ruses of war include e.g. the use of enemy signals, passwords, signs, decoys, etc.; not, however, espionage. 
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, § 471; see also § 1018 (naval warfare).
In 2010, in the Chechen Refugee case, Germany’s Federal Administrative Court was called upon to decide whether a Russian refugee claimant from Chechnya had to be excluded from refugee protection because there were serious reasons for considering that he had committed a war crime in Chechnya in 2002 by killing two Russian soldiers and taking a Russian officer hostage. The Court stated: “In some cases, unlawful perfidy and lawful ruses of war are difficult to distinguish”. 
Germany, Federal Administrative Court, Chechen Refugee case, Judgment, 16 February 2010, § 37.