The Third Reich Heer(army) and Luftwaffe(airforce) NCO rank of Unteroffizier is equivalent to that of Sergeant in the current day US Army and USAF. The Kriegsmarine equivalent of the Unteroffizier was called Maat(etymologically related to the English "mate") whereas the Waffen-SS equivalent was the SS-Unterscharführer.
For a more complete overview
of which ranks existed
, see Wehrmacht ranks
This rank is not only of historic interest, as it still exists in the modern Bundeswehr, the modern German army. Thanks to Datajunkie for pointing that out.
The page that helped me with this writeup is no longer on the internet, but it used to live at www.wehrmacht-association.com/Open_Pages/ranks.htm