Irregular military is any military component distinct from a country's regular armed forces, representing non-standard militant elements outside of conventional governmental backing. Irregular element
Chouans hiding behind a dolmen
British SAS patrol in armed jeeps during the North African campaign of World War II
A group of Ottoman bashi-bazouks in Bulgaria, irregular soldiers of the military of the Ottoman Empire, 1877–1878
Gardner's Irregular Horse of Hindustani Mahomedans
Francs-tireurs were irregular military formations deployed by France during the early stages of the Franco-Prussian War. The term was revived and used by partisans to name two major French Resistance
Capture of a Franc-tireur, by Carl Johann Lasch
Francs-tireurs in the Vosges during the Franco-Prussian War
Berne-Bellecour, Les Tirailleurs de la Seine au combat de Rueil-Malmaison (1875).
Francs-tireurs and Allied paratroopers during the Battle of Normandy in 1944