Unteroffizier is both a specific military rank as well as a collective term for non-commissioned officers of the German military that has existed since the 19th century. The rank existed as a title as early as the 17th century with the first widespread usage occurring in the Bavarian Army of the 19th century. The term continues to be used by the Bundeswehr.
There are two classes of non-commissioned officers (in the following, the titles of the German Navy [Deutsche Marine] are given in brackets):
Informally, the non-commissioned officers with portepee are often called "the Feldwebel [Bootsmann] ranks" or even altogether Feldwebel [Bootsleute], which creates a similar confusion as exists already with the word Unteroffizier. In the navy, the official terms remain more common. The word Unteroffizier, in turn, is getting a third meaning, namely: non-commissioned officer without portepee, as opposed to Feldwebel. Note that officers and Feldwebel are together referred to by the unofficial but common term "Dienstgrade" (literally: "military ranks", but used on persons - though of course the lower ranks are ranks as well), whereas Unteroffiziere and Stabsunteroffiziere are excluded, maybe with the exception of basic training units.
Unteroffizier translates as "under-officer" or "sub-officer" and, when meaning the specific rank, is the equivalent to an American sergeant. The main difference consists in the fact that adverse to the British or American Army the German Army relied on compulsory conscription since at least 1870. In times of peace an Unteroffizier was a career soldier who trained conscripts or led squads and platoons. He could rise through the ranks to become an "Unteroffizier mit Portepee", i.e. a Feldwebel, which was the highest rank a career soldier could reach. Since the German officer corps was immensely class conscious a rise through the ranks from a NCO to become an officer was hardly possible except in times of war. The Unteroffizierskorps was made up of professional soldiers which formed the backbone of German armies. This tradition has not been changed by the Bundeswehr which is a classical conscript army but where all ranks of Unteroffizier and up consist only of professional soldiers who sign up for a period extending consciption.
Unteroffizier is one of the few German military ranks whose insignia has remained unchanged over the past one hundred years. The shoulder boards of a modern Unteroffizier are relatively similar to the World War I and World War II designs.
During the Second World War, in the German Wehrmacht, an Unteroffizier in an infantry platoon normally commanded a squad of 9 or 10 men, and was thus equivalent to an American Army sergeant or a British Army corporal. The "equivalent" rank is therefore given as both of these ranks depending on which references are consulted.
A modern day German Bundeswehr Army Unteroffizier typically commands squad sized formations or acts as an assistant platoon NCO. The rank is also used in the modern-day German Luftwaffe. In the Bundeswehr the grade of Stabsunteroffizier (a Junior NCO) ranks between Unteroffizier and Feldwebel (a Senior NCO).