[9] One of the earliest known uses of the term irregular warfare is a 1906 article for the United Kingdom War Office in 1906, where Colonel Charles Callwell, in defining Small Wars, noted: "Small wars include the partisan warfare which usually arises when trained soldiers are employed in the quelling of sedition and of insurrections in civilised countries; they include campaigns of conquest when a Great Power adds the territory of barbarous races to its possessions; and they include punitive expeditions against tribes bordering upon distant colonies....Whenever a regular army finds itself engaged upon hostilities against irregular forces, or forces which in their armament, their organization, and their discipline are palpably inferior to it, the conditions of the campaign become distinct from the conditions of modern regular warfare, and it is with hostilities of this nature that this volume proposes to deal.
Upon the organization of armies for irregular warfare valuable information is to be found in many instructive military works, official and non-official.
"[10] A similar usage appears in the 1986 English edition of "Modern Irregular Warfare in Defense Policy and as a Military Phenomenon" by former Nazi officer Friedrich August Freiherr von der Heydte.
The original 1972 German edition of the book is titled "Der Moderne Kleinkrieg als Wehrpolitisches und Militarisches Phänomen".
"[11] The word "Irregular," used in the title of the English translation of the book, seems to be a reference to non "regular armed forces" as per the Third Geneva Convention.