The origin of the term blitzkrieg is obscure. It was never used in the title of a military doctrine or handbook of the German Army or Air Force,[8] and no "coherent doctrine" or "unifying concept of blitzkrieg" existed; German High Command mostly referred to the group of tactics as "Bewegungskrieg" (Maneuver Warfare).[19] The term seems to have been rarely used in the German military press before 1939, and recent research at the German Militrgeschichtliches Forschungsamt, at Potsdam, found it in only two military articles from the 1930s.[e] Both used the term to mean a swift strategic knockout, rather than a radically new military doctrine or approach to war.