Related Rule
Germany
Practice Relating to Rule 3. Definition of Combatants
Germany’s Military Manual (1992) states:
The armed forces of a party to a conflict consist of combatants and non-combatants. Combatants are persons who may take a direct part in hostilities, i.e. participate in the use of a weapon or a weapon-system in an indispensable function. The other members of the armed forces are non-combatants. 
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, § 301.
The manual specifies:
Persons who are members of the armed forces but … do not have any combat mission, such as judges, government officials and blue-collar workers, are non-combatants … Members of the medical service and religious personnel (chaplains) attached to the armed forces are also non-combatants. 
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, §§ 313–314.
Germany’s Soldiers’ Manual (2006) states: “Combatants are all persons who may directly participate in combat operations, e.g. the members of the armed forces as well as militias and volunteer corps forming part of the armed forces.” 
Germany, Druckschrift Einsatz Nr. 03, Humanitäres Völkerrecht in bewaffneten Konflikten - Grundsätze, Erarbeitet nach ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten - Handbuch, DSK SF009320187, Bundesministerium der Verteidigung, R II 3, August 2006, p. 2.
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 (ISAF) 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:
1.
There is a non-international armed conflict in Afghanistan in the sense of the International Crimes Code (§§ 8 ff VStGB) and of international humanitarian law:
aa)
The international ISAF forces led by NATO are present in the country with the consent of the Afghan government. Therefore, there is an agreement by the State on whose territory the armed conflict is taking place to the ISAF deployment which is valid under international law. Under international law, the conflict must be qualified as non-international despite the participation of international forces because ISAF is fighting on the side of the Afghan State …
d)
The existence of a non-international armed conflict [in Afghanistan] leads to the application of the International Crimes Code and, via Art. 25 GG [Basic Law], of the entire international law of armed conflict. This means that soldiers of the armed forces (Bundeswehr) in the context of the ISAF deployment – in contrast to insurgents – are regular combatants who may not be prosecuted for acts of war which are lawful under international law. 
Germany, Federal Court of Justice, Federal Prosecutor General, Fuel Tankers case, Decision, 16 April 2010, pp. 41–42 and 45.
The Federal Prosecutor General also stated:
The following is to be considered regarding the subjective element of § 11 (1) (3) VStGB [according to which 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. Art. 50 (1) AP [1977 Additional Protocol] I contains a definition of the term “civilian” for international armed conflicts. Accordingly any person “who does not belong to one of the categories of persons referred to in Art. 4 paragraph A sub-paragraphs (1), (2), (3) and (6) of the [1949 Geneva] Convention III and in Article 43 of this Protocol is a civilian”. Therefore members of armed forces or of organized armed groups (militias and volunteer corps) of a party to the conflict and of a levée en masse are not civilians … In non-international armed conflict fighters of the non-State party are not soldiers akin to members of a State’s armed forces who visibly distinguish themselves through uniform, insignia etc. and whose hierarchy, powers and salaries etc. are regulated by law. Rather, they obtain their status merely by being functionally incorporated into a non-State armed group which has a certain degree of organization. They often have a regular full-time or part-time civilian job (“farmer by day, fighter by night”). Nevertheless they are not considered as civilians under current international law who only assume the role of a fighter during the limited duration of ongoing armed hostilities and constitute a lawful military objective during such time only. If they have functionally joined an organized armed group in a non-international armed conflict as fighters, they are retaining this status as armed fighters until they have recognizably and finally given up this function … The opinion previously expressed in the literature according to which they are to be considered as civilians who may only be attacked during their participation in hostilities … is to be considered as a minority opinion which has not been representative at least since the publication of the Interpretative Guidance of the International Committee of the Red Cross in June 2009 … State practice in non-international armed conflict never reflected this opinion and in addition it is not reconcilable with the principle of distinction which is generally recognized as customary international law …
The fuel tankers had been abducted by an organized group of armed Taliban whose members were thus not civilians. 
Germany, Federal Court of Justice, Federal Prosecutor General, Fuel Tankers case, Decision, 16 April 2010, pp. 47–48; see also p. 60.
In 2010, in reply to a Minor Interpellation in the Bundestag (Lower House of Parliament) titled “Information on the 33 individuals detained by the German ISAF [International Security Assistance Force] contingent”, Germany’s Federal Government wrote: “Individuals who are participating in the hostilities against ISAF or the Afghan State are not combatants. Therefore they may be criminally prosecuted for their participation in hostilities.” 
Germany, Lower House of Federal Parliament (Bundestag), Reply by the Federal Government to the Minor Interpellation by Members Volker Beck (Cologne), Tom Koenigs, Marieluise Beck (Bremen), further Members and the Parliamentary Group DIE LINKE, BT-Drs. 17/2551, 12 July 2010, p. 4.
In 2010, in reply to a Minor Interpellation in the Bundestag (Lower House of Parliament) titled “Compensation for the victims of the Kunduz bombardment in the night of 4 September 2009”, Germany’s Federal Government wrote:
5. Based on which criteria and evidence does the Federal Government conclude that a person is to be considered an “enemy fighter” and in which way is the principle of the [1977] Additional Protocol I to the Geneva Conventions, which states that in case of doubt a person is to be considered a civilian, taken into consideration?
In the context of a non-international armed conflict, international humanitarian law permits governmental troops and troops supporting them to use direct military force against civilians … continuously participating in hostilities based on their role and function within the enemy forces. Whether a person fulfils these conditions depends on the circumstances of the individual case. 
Germany, Lower House of Federal Parliament (Bundestag), Reply by the Federal Government to the Minor Interpellation by Members Christine Buchholz, Sevim Dağdelen, Inge Höger, further Members and the Parliamentary Group DIE LINKE, BT-Drs. 17/3723, 11 November 2010, p. 3.