Matrose was the lowest rate in the Kriegsmarine, the navy of the Third Reich. Between 1939 and 1945, the ranks of the Kriegsmarine swelled to over 1 500 000, and most of these(i.e. more than 50%) served as Matrosen.
The Luftwaffe equivalent to Matrose was the Flieger, the Heer equivalent was the Grenadier and the Waffen-SS equivalent was the SS-Schütze. The equivalent US Navy rate is the Seaman.
It should be noted that the word "rate" applies to naval enlisted personnel. "Rank" is the airforce and army word.
For a more complete overview of which ranks existed, see Wehrmacht ranks.
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