Each ship carried twelve SK L/45 guns. The wing turrets were Drh LC/1906 mounts, as were the centerline turrets on the first two ships of the class, "Nassau" and "Westfalen". "Posen" and "Rheinland" carried their centerline guns in Drh LC/1907 turrets, which had a longer trunk than the LC/1906 design. The Drh LC/1906 turrets and 28 cm SK/L45 guns were designed specifically for the new German dreadnoughts in 1907. Both mountings allowed for elevation up to 20 degrees, but the LC/1907 mounts could depress an additional two degrees, down to −8. The main battery propellant magazines were placed above shell rooms, with the exception of the centerline turrets of "Nassau" and "Westfalen". These guns fired 666 lb shells, with a fore propellant charge in silk bags and a main charge in a brass case. The guns fired the shells at a muzzle velocity of and they had a maximum range of .