Related Rule
Germany
Practice Relating to Rule 8. Definition of Military Objectives
Section B. Armed forces
Germany’s Military Manual (1992) provides that military objectives include, in particular, armed forces. 
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, § 443.
In 2010, in the Fuel Tankers case, the Federal Prosecutor General at Germany’s Federal Court of Justice investigated whether war crimes or other crimes under domestic law had been committed in the course of an airstrike which was ordered by a colonel (Oberst) of the German armed forces against two tankers transporting fuel for the International Security Assistance Force in Afghanistan stolen by the Taliban near Kunduz and which resulted in the deaths of a number of civilians. The Federal Prosecutor General stated:
Pursuant to § 170 para. 2 StPO [Penal Procedure Code], the investigation proceedings which were initiated by the order of 12 March 2010 against Colonel (Oberst) Klein and Company Sergeant Major (Hauptfeldwebel) Wilhelm due to suspected offences under the VStGB [International Crimes Code] and other offences are to be terminated as a result of the investigations conducted and based on the sources of information set out hereafter and on the reasons given in detail hereafter. 
Germany, Federal Court of Justice, Federal Prosecutor General, Fuel Tankers case, Decision, 16 April 2010, p. 1.
The Federal Prosecutor General also stated:
The following is to be considered regarding the subjective element of § 11 (1) (3) VStGB [which states that carrying out an attack by military means and definitely anticipating that the attack will cause death or injury to civilians or damage to civilian objects on a scale out of proportion to the concrete and direct overall military advantage anticipated is a war crime in international and non-international armed conflict]:
aa)
Insurgents who continuously take part in the armed conflict, as the Taliban in this case, are not civilians but legitimate military objectives which may be lawfully attacked even outside of ongoing armed hostilities. 
Germany, Federal Court of Justice, Federal Prosecutor General, Fuel Tankers case, Decision, 16 April 2010, p. 47.
The Federal Prosecutor General further stated:
aa)
It is not questioned that the armed Taliban fighters who abducted the fuel tankers and who make up a significant part of the victims of the bombing were members of an organized armed group which is a party to the armed conflict. These fighters thus constitute a legitimate military objective whose “destruction” is legal within the limits of military necessity. 
Germany, Federal Court of Justice, Federal Prosecutor General, Fuel Tankers case, Decision, 16 April 2010, p. 60.