The Nassau class was a group of four German dreadnought battleships built for the German Kaiserliche Marine (Imperial Navy) in the mid-1900s. The class comprised Nassau, the lead ship, Rheinland, Posen, and Westfalen. All four ships were laid down in mid-1907, and completed by late 1910. Though commonly perceived as having been built in response to the British Dreadnought, their design traces its origin to 1903; they were in fact a response to Dreadnought's predecessors of the Lord Nelson class. The Nassaus adopted a main battery of twelve 28 cm (11 in) guns in six twin-gun turrets in an unusual hexagonal arrangement. Unlike many other dreadnoughts, the Nassau-class ships retained triple-expansion steam engines instead of more powerful steam turbines.