"Sturmführer" is an SS-rank equivalent to 2nd Lieutenant. The equivalent to Major was: "Sturmbahnführer"

From Second Lieutenant to Kolonel the ranks were:
- Sturmführer
- Obersturmführer
- Hauptsturmführer
- Sturmbahnführer
- Obersturmbahnführer
- Standartenführer

He served in the SS, nothing to do with grenadiers, other than that both were considered elite.