In time of war, their role was to protect the Imperial headquarters, to escort prisoners and occasionally to enforce the law and limit civil disorder in conquered cities.

The gendarmerie played a secondary role in the first campaigns of the Napoleonic Wars, ensuring the movements of the Emperor and the protection of lines of communication.

Sent to Spain in 1808, the unit conducted counter-insurgency operations against Spanish guerrillas in addition to its usual service as a public force, sometimes also acting as heavy cavalry such as in Medina de Rioseco.

Recalled from the peninsula in 1812 for the Russian campaign, the elite gendarmes of the Guard saw combat at the Battle of the Berezina, then at Leipzig, Montmirail and Vauchamps during the War of the Sixth Coalition.

Renamed the Gendarmes des chasses du roi under the First Bourbon Restoration, the gendarmerie retook its old name during the Hundred Days and took part in the Waterloo campaign.

A first detachment of 5 officers and 100 gendarmes, commanded by Captain Noirot, was attached to Marshal Bessières' corps where it fulfilled its usual security role.

A few months later, on 14 July, at the Battle of Medina de Rioseco, 57 elite gendarmes led by Captain Noirot charged the Spanish positions with General Lasalle's cavalry.

At the he Battle of Burgos on 10 November, the elite gendarmes within Bessières' cavalry took part in the charge that pushed back the Spanish and secured the city for the French.

[6] In early 1809, Napoleon, leaving Marshal Soult to pursue the British, returned to France and recalled most of his Guard for the campaign against Austria.

[7] In early 1811, the gendarmerie of the Guard in Spain consisted of a 77-men detachment commanded by Captain Jamin, attached to the corps of General Dorsenne, where it fulfilled the dual role of security and counter-insurgency.

For this reason, other troops of the Grande Armée nicknamed them "The Immortals" (Les Immortels), as they were less engaged in combat than other units and thus had fewer personnel killed in action.

[14] At times of peace when the Emperor resided in his palaces, the elite gendarmerie was responsible for guarding the imperial apartments, monitoring the entrances and exits of buildings.

During the Hundred Days, the Emperor gave command of the elite gendarmerie to General Pierre Dautancourt [fr], who was responsible for its organization, although it was Captain Dyonnet who effectively led the unit in the Waterloo campaign.

They wore a tall bearskin cap with a visor, topped by a red round cloth patch nicknamed cul-de-singe ("monkey bottom") with a white grenade embroidered on it.

In 1815, crested helmets with black manes (red for trumpeters) were introduced but not completed, so the elite gendarmes fought their last campaign with mixed headgears.