The Departmental Gendarmerie (Gendarmerie Départementale), also named «La Blanche» (The White), is the most numerous part of the Gendarmerie, is in charge of policing small towns and rural areas. Its territorial divisions are based on the administrative divisions of France, particularly the departments from which the Departmental Gendarmerie derives its name. The Departmental Gendarmerie carries out the general public order duties in municipalities with a population of up to 20,000 citizens. When that limit is exceeded, the jurisdiction over the municipality is turned over to the National Police.
It is divided into 13 metropolitan regions (including Corsica), themselves divided into groupements (one for each of the 100 département, thus the name), themselves divided into compagnies (one for each of the 342 arrondissements).
It maintains gendarmerie brigades throughout the rural parts of the territory. There are two kind of brigades:
· Large autonomous territorial brigades (BTAs)
· Brigade groups composed of smaller brigades supervised by a larger one (COBs).
In addition, it has specialised units:
· Research units, who conduct criminal investigations when their difficulty exceeds the abilities of the territorial units
· Surveillance and intervention platoons (PSIGs), who conduct roving patrols and reinforce local units as needed.
· Specialized brigades for prevention of juvenile delinquency
· Highway patrol units.
· Mountain units, specialised in surveillance and search and rescue operations, as well as inquiries in mountainous areas
In addition, the Gendarmerie runs a national criminal police institute (Institut de recherche criminelle de la gendarmerie nationale) specializing in supporting local units for difficult investigations.
The research units may be called into action by the judiciary even within cities (i.e. in the National Police's area of responsibility). As an example, the Paris research section of the Gendarmerie was in charge of the investigations into the vote-rigging allegations in the 5th district of Paris (see corruption scandals in the Paris region).
Gendarmes normally operate in uniform. They may operate in plainclothes only for specific missions and with their supervisors' authorisation.